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Chemical reaction

A chemical reaction is a process that results in the interconversion of chemical substances ^[1]. The substance or substances initially involved in a chemical reaction are called reactants. Chemical reactions are characterized by a chemical change and it yields one or more products which are different from the reactants. Classically, chemical reactions encompass changes that strictly involve the motion of electrons in the forming and breaking of chemical bonds, although the general concept of a chemical reaction, in particular the notion of a chemical equation, is applicable to transformations of elementary particles, as well as nuclear reactions.

Many different chemical reactions are used in combinations in chemical synthesis in order to get a desired product. In biochemistry, series of chemical reactions form metabolic pathways, since straight synthesis of a product would be energetically impossible in conditions within a cell. Chemical reactions are also divided into organic reactions and inorganic reactions.

Contents 1 Reaction types 2 Thermochemistry 2.1 Chemical equilibrium 2.2 Exothermic reactions 2.3 Endothermic reactions 3 Chemical kinetics 4 See also 5 External links 6 References

Reaction types

Chemical reactions may be classified in different ways depending on the particular aspect considered for elaborating the division, or on the branch of Chemistry which the classification originates from. Some examples of widely used terms for describing common kinds of reactions are:

• Isomerisation, in which a chemical compound undergoes a structural rearrangement without any change in its net atomic composition; see stereoisomerism
• Direct combination or synthesis, in which two or more chemical elements or compounds unite to form a more complex product:

2H₂ (g) + O₂ (g) → 2H₂O (l)

• Chemical decomposition or analysis, in which a compound is decomposed into smaller compounds or elements:

2H₂O (l) → 2H₂ (g) + O₂(g)

• Single displacement or substitution, characterized by an element being displaced out of a compound by a more reactive element:

2Na(cr) + 2HCl (aq) → 2NaCl (aq) + H₂ (g)

• Double displacement or coupling substitution , in which two compounds in aqueous solution (usually ionic) exchange elements or ions to form different compounds:

NaCl (aq) + AgNO₃ (aq) → NaNO₃ (aq) + AgCl (s)

• Combustion, in which any combustible substance combines with an oxidizing element, usually oxygen, to generate heat and form oxidized products. The term combustion is used usually only for reactions that destroy complex molecules, i.e. a controlled oxidation of a single functional group is not combustion.

C₁₀H₈ (g) + 14O₂ (g) → 10CO₂ (g) + 4H₂O (g) + heat

CH₂S + 6 F₂ → CF₄ + 2 HF + SF₆ + heat

Some branches of chemistry include any minor changes in chemical conformation in the reaction types, while others consider these changes merely as physical properties of a compound.

The collision of more than two particles into the ordered structure necessary to perform chemical transformations is extremely unlikely; which is why ternary reactions in practice are not observed. A chemical reaction may require three or more reagents, but the process can generally be decomposed into a stepwise series or a set of stepwise reactions of the above.

The large diversity of chemical reactions makes it difficult to establish simple criteria for functional (as opposed to mechanistic) classification. However, some kinds of reactions have similarities which make it possible to define some larger groups. A few examples are:

• Organic reactions encompass several different kinds of reactions involving compounds which have carbon as the main element in their molecular structure. These reactions occur mostly according to, within, by, or via functional groups.

• Petrochemical reactions are often distinguished from other organic reactions.

• Redox reactions involve augmenting or decreasing the electrons associated with a particular atom. according to its oxidation number.
• Combustion, in which a substance reacts with an oxidizing element, such as oxygen gas.

Reactions are also classified according to their mechanism:

• Reactions of ions, e.g. disproportionation of hypochlorite
• Reactions with reactive ionic intermediates, e.g. reactions of enolates
• Radical reactions, e.g. combustion at high temperature
• Reactions of carbenes

Thermochemistry

See main article: Thermochemistry.

Thermochemistry deciphers whether a specific chemical reaction can or cannot occur. Thermodynamics (or what is now known as equilibrium thermodynamics) understands the reaction in terms of the initial and final states of the reaction mixture.

Reactions very seldom occur directly. Usually, reactants must collide to form an activated complex. This complex has a higher internal energy than the original reactants combined, having gained some from the kinetic energy of the reactant substances’ collision. This energy allows for the rearrangement of bonds which constitutes the reaction. In some reactions, the reactants may pass through several reactive intermediates before becoming products.

Thermodynamics does not attempt to figure out the process by which a reaction occurs. This field of study is taken up by the field of chemical kinetics. Another question “How fast is the reaction?” is also left completely unanswered by it. Chemical kinetics attempts to put all these phenomena into perspective.

Chemical equilibrium

Every chemical reaction is, in theory, reversible. In a forward reaction the substances defined as reactants are converted to products. In a reverse reaction products are converted into reactants.

Chemical equilibrium is the state in which the forward and reverse reaction rates are equal, thus preserving the amount of reactants and products. However, a reaction in equilibrium can be driven in the forward or reverse direction. This is done by changing the reaction conditions such as temperature or pressure. Le Chatelier’s principle can be used to predict whether products or reactants will be formed.

Although all reactions are reversible to some extent, some reactions can be classified as irreversible. An irreversible reaction is one that “goes to completion.” This phrase means that nearly all of the reactants are used to form products. These reactions are very difficult to reverse even under extreme conditions.

Exothermic reactions

According to energy balance criteria, that is, chemical reaction equilibria criteria, any closed system will tend to minimize its free energy. Without any outside influence, any reaction mixture, too, will try to do the same. For many cases, an analysis of the enthalpy of the system will give a decent account of the energetics of the reaction mixture. The enthalpy of a reaction is calculated using standard reaction enthalpies and the Hess’ law of constant heat summation. Many of these enthalpies may be found in beginners’ books on thermodynamics. For example, consider the combustion of methane in oxygen:

CH₄ + 2 O₂ → CO₂ + 2 H₂O

By calculating the amounts of energy required to break all the bonds on the left (”before”) and right (”after”) sides of the equation using collected data, it is possible to calculate the energy difference between the reactants and the products. This is referred to as ΔH, where Δ (Delta) means difference, and H stands for enthalpy, a measure of energy which is equal to the heat transferred at constant pressure. ΔH is usually given in units of kilojoules (kJ) or in kilocalories (kcal).

If ΔH is negative for the reaction, then energy has been released often in the form of heat. This type of reaction is referred to as an exothermic reaction (literally, outside heat, or throwing off heat). An exothermic reaction is more favourable and thus more likely to occur. An example reaction is combustion, known from everyday experience, since burning gas in air produces heat.

Endothermic reactions

A reaction may have a positive ΔH. If a reaction has a positive ΔH, it consumes energy as the reaction moves towards completion. This type of reaction is called an endothermic reaction (literally, inside heat, or absorbing heat).

The above rule, “Exothermic reactions are favourable”, is usually true. However, there may be situations where exothermic reactions may not be favourable. This happens when the stability obtained due to loss of enthalpy is off set by a corresponding decrease in entropy (a measure of disorder). The exact rule is that a reaction is favourable when the Gibbs free energy of that reaction is negative where ΔG = ΔH − TΔS; ΔG being the change in Gibbs free energy, ΔH being the change in enthalpy, and ΔS is the change in entropy

A reaction is called spontaneous if its thermodynamically favoured, by that meaning that it causes a net increase on entropy. Spontaneous reactions (in opposition to non-spontaneous reactions) do not need external perturbations (such as energy supplement) to happen. In a system at chemical equilibrium, it is expected to have larger concentrations of the substances formed by the spontaneous direction of the process.

Thus, in a global isolated system (which it strictly isn’t, see entropy), spontaneous reactions may be understood to occur without human interference. Most spontaneus reactions in this system are exothermic (such as rusting) or metamorphism, thus increasing the global entropy, though photosynthesis is an important exception (in a global system).

Chemical kinetics

See main article: Chemical kinetics.

The rate of a chemical reaction is a measure of how the concentration of the involved substances changes with time. Analysis of reaction rates is important for several applications, such as in chemical engineering or in chemical equilibrium study. Rates of reaction depends basically on:

• Reactant concentrations, which usually make the reaction happen at a faster rate if raised,
• Surface Area, the amount of the substance being used,
• Pressure, By increasing the pressure, you squeeze the molecules together so you will increase the frequency of collisions between the molecules.
• Activation energy, which is defined as the amount of energy required to make the reaction start and carry on spontaneously. Higher activation energy implies that a reaction will be harder to start and, therefore, slower.
• Temperature, which hastens reactions if raised, because higher temperature means that the involved species will have more energy, thus making the reaction easier to happen,
• The presence or absence of a catalyst. Catalysts are substances which change the pathway (mechanism) of a reaction which in turn increases the speed of a reaction by lowering the activation energy needed for the reaction to take place. A catalyst is not destroyed or changed during a reaction, so it can be used again.

Reaction rates are related to the concentrations of substances involved in reactions, as quantified by the law of mass action. Reactions whose rates are independent of reactant concentrations are called zero-order reactions.

See also

• List of reactions
• List of publications in chemistry

External links

• Rate of reaction
• Chemical Management

References

1. ↑ IUPAC Gold Book Definition

Chemical substance

A chemical substance is any material substance used in or obtained by a process in chemistry. It can be an element, a compound, or a mixture thereof:

• A chemical element is a substance that cannot be divided or changed into different substances by ordinary chemical methods. The smallest particle of such an element is an atom, which consists of electrons centered about an nucleus of protons and neutrons.

• A chemical compound is a substance consisting of two or more chemical elements that are chemically combined in fixed proportions.

• A molecule is the smallest particle of an element or compound that retains the chemical characteristics of the element or compound.

• An ion is an atom or group of atoms with a net electric charge, having lost (cation) or gained (anion) an electron.

• The term “chemical” may refer to any chemical substance, though a popular meaning is “a product of the chemical industry”. As such the term may carry connotations of being “unnatural” and perhaps harmful, even when such fears are unjustified, as with the dihydrogen monoxide hoax.

Chemical synthesis

In chemistry, chemical synthesis is purposeful execution of chemical reactions in order to get a product, or several products. This happens by physical and chemical manipulations usually involving one or more reactions. In modern laboratory usage, this tends to imply that the process is reproducible, reliable, and established to work in multiple laboratories.

A chemical synthesis begins by selection of compounds that are known as reagents or reactants. Various reaction types can be applied to these to synthesize the product, or an intermediate product. The amount of product in a chemical synthesis is the reaction yield. Typically, yields are expressed as a weight in grams or as a percentage of the total theoretical quantity of product that could be produced. See chemical equilibrium.

In the total synthesis of a complex product it may take multiple steps to synthesize the product of interest, and inordinate amounts of time. Skill in organic synthesis is prized among chemists and the synthesis of exceptionally valuable or difficult compounds has won chemists such as Robert Burns Woodward the Nobel Prize for Chemistry. If a chemical synthesis starts from basic laboratory compounds and yields something new, it is a purely synthetic process. If it starts from a product isolated from plants or animals and then proceeds to a new compounds, the synthesis is described as a semisynthetic process.

Many strategies exist in chemical synthesis that go beyond converting reactant A to reaction product B. In cascade reactions multiple chemical transformations take place within a single reactant, in multi-component reactions up to 10 different reactants form a single reaction product and in a telescopic synthesis one reactant goes through multiple transformations without isolation of intermediates.

The word synthesis in the present day meaning was first used by the chemist Adolph Wilhelm Hermann Kolbe.

The other meaning of chemical synthesis is narrow and restricted to a specific kind of chemical reaction, a direct combination reaction, in which two or more reactants combine to form a single product. The general form of a direct combination reaction is:

A + B → AB

where A and B are elements or compounds, and AB is a compound consisting of A and B. Examples of combination reactions include:

2Na + Cl₂ → 2 NaCl (formation of table salt)

S + O₂ → SO₂ (formation of sulfur dioxide)

4 Fe + 3 O₂ → 2 Fe₂O₃ (iron rusting)

CO₂ + H₂O → H₂CO₃ (carbon dioxide dissolving and reacting with water to form carbonic acid)

4 special synthesis rules:

metal-oxide + H₂O → metal(OH)

non-metal-oxide + H₂O → oxi-acid

metal-chloride + O₂ → metal-chloride

metal-oxide + CO₂ → metal(CO₃)

See also

• Chemical engineering
• Template-directed synthesis
• Organic synthesis
• Total synthesis
• Peptide synthesis

Chemical trap

in chemistry, a chemical trap is a chemical compound that is used to detect a certain molecule when

• the concentration of this molecule is very small and below detection limit
• the molecule is very reactive and it not possible to isolate or detect it by spectroscopic means
• the molecule is an enantiomer present in a racemate.

With the reaction product of the chemical trap and the molecule in question it is possible to

• quantify the amount
• prove the existence of the molecule

Chemistry

Chemistry (derived from alchemy) is the science of matter at or near the atomic scale. In this pursuit chemistry deals with the properties of such matter, the transformations of matter and the interactions of matter with other matter and with energy. Chemistry primarily studies atoms and collections of atoms such as molecules, crystals or metals that make up ordinary matter. According to modern chemistry it is the structure of matter at the atomic scale that is determinant of the nature of any given matter.

Contents 1 Introduction 2 History of chemistry 3 Chemical phenomena 4 Subdisciplines of chemistry 5 Fundamental concepts 5.1 Nomenclature 5.2 Atoms 5.3 Elements 5.4 Compounds 5.5 Molecules 5.6 Ions 5.7 Substance 5.8 Bonding 5.9 States of matter 5.10 Chemical reactions 5.11 Quantum chemistry 5.12 Chemical Laws 6 Etymology 7 See also 8 External links 9 Further reading

Introduction

Chemistry is often called the central science because it connects other sciences together, such as physics, biology or geology. Chemistry encompasses many specific specialized sub-disciplines that often overlap with significant portions of other sciences. Sub-disciplines, however, are very specific to chemistry, for example, they allow the manufacturing and testing of stronger materials, the synthesis of pharmaceuticals to treat disease, and determination of the mechanisms behind life processes.

A fundamental component of chemistry is that matter is involved. Chemistry may involve the interaction of matter with matter, or, involve matter with non-material phenomena such as energy. Most central and traditional to chemistry is the interaction of one substance with another such as in a chemical reaction where one substance or substances is transformed into another. This may involve electromagnetic radiation (as in photochemistry) where a chemical reaction is driven by the stimulation of light. However the chemical reaction is only part of a larger field that also studies matter in other ways. Chemical spectroscopists for example study the interaction of light with matter often without any reaction occurring.

Scientists who profess chemistry are known as chemists. According to contemporary chemists all ordinary matter consists of atoms or the sub atomic components that make up atoms. Atoms may be combined to produce more complex forms of matter such as ions, molecules or crystals. The structure of the world we commonly experience and the properties of the matter we commonly interact with are determined by properties of chemical substances and their interactions. Steel is hard because its atoms are bound together in a crystalline lattice. Wood burns because it can react spontaneously with oxygen in a chemical reaction above a certain temperature. Water is a liquid at room temperature because its molecules move about more than in a solid but less than in a gas. One can see because of the interaction of light with protein molecules in the back of ones eye.

With such a large area of study, it is impossible to know everything about chemistry and very difficult to summarize the field concisely. Even the most knowledgeable, experienced chemist only knows a very narrow area of chemistry better than others, though most chemists have a general knowledge of many areas of chemistry. Chemistry is divided into many areas of study called sub-disciplines in which chemists specialize. The chemistry taught at the high school or early college level is often called “general chemistry” and is intended to be an introduction to a wide variety of fundamental concepts and to give the student the tools to continue on to more advanced subjects. Many concepts presented at this level are often incomplete and technically inaccurate, yet they are of extraordinary utility. Chemists regularly use these simple, elegant tools and explanations in their work because the best solution possible is often so overwhelmingly difficult and the true solution is usually unobtainable.

The science of chemistry is historically a recent development but has its roots in alchemy which has been practiced for millennia throughout the world. The word chemistry is directly derived from the word alchemy; however, the etymology of alchemy is unclear (see alchemy).

History of chemistry

Main article: History of chemistry

The roots of chemistry can be traced to the phenomenon of burning. Fire was a mystical force that transformed one substance into another and thus was of primary interest to mankind. It was fire that led to the discovery of iron and glass. After gold was discovered and became a precious metal, many people were interested to find a method that could convert other substances into gold. This led to the protoscience called Alchemy. Alchemists discovered many chemical processes that led to the development of modern chemistry. Chemistry as we know it today, was invented by Antoine Lavoisier with his law of Conservation of mass in 1783. The discoveries of the chemical elements has a long history culminating in the creation of the periodic table by Dmitri Mendeleev. The Nobel Prize in Chemistry created in 1901 gives an excellent overview of chemical discovery in the past 100 years.

Chemical phenomena

A chemical phenomenon is a phenomenon that is describable by chemistry and involves substances and energy. Chemical phenomena are associated with a change in the properties of the substance as a result of a chemical reaction. Fire is undoubtedly the most spectacular chemical phenomenon. Chemists strive to explain all known chemical phenomena, to discover others and group chemical phenomena into classes with common causes or effects. For example, substances that react with oxygen to produce other substances are said to undergo oxidation; similarly a group of substances called acids or alkalis can react with one another to neutralize each other’s effect, a phenomenon known as neutralization. Substances can also be dissociated or synthesized from other substances by various different chemical processes. A chemical reaction is often accompanied by evolution or absorption of energy, this phenomenon is studied under a subdiscipline of chemistry called chemical thermodynamics/ thermochemistry. Similarly certain substances emit light without being heated, a phenomenon known as phosphorescence.

Subdisciplines of chemistry

Chemistry typically is divided into several major sub-disciplines. There are also several main cross-disciplinary and more specialized fields of chemistry.

• Analytical chemistry is the analysis of material samples to gain an understanding of their chemical composition and structure. Analytical chemistry incorporates standardized experimental methods in chemistry. These methods may be used in all subdiciplines of chemistry, excluding purely theoretical chemistry.

• Biochemistry is the study of the chemicals, chemical reactions and chemical interactions that take place in living organisms. Biochemistry and organic chemistry are closely related f.e. in medicinal chemistry.

• Inorganic chemistry is the study of the properties and reactions of inorganic compounds. The distinction between organic and inorganic disciplines is not absolute and there is much overlap, most importantly in the sub-discipline of organometallic chemistry.

• Organic chemistry is the study of the structure, properties, composition, mechanisms, and reactions of organic compounds. In other words, it is the study of those substances that contain carbon.

• Physical chemistry is the study of the physical basis of chemical systems and processes. In particular, the energetics and dynamics of such systems and processes are of interest to physical chemists. Important areas of study include chemical thermodynamics, chemical kinetics, electrochemistry, statistical mechanics, and spectroscopy. Physical chemistry has large overlap with molecular physics. Physical chemistry involves the use of calculus in deriving equations.

• Theoretical chemistry is the study of chemistry via theoretical reasoning (usually within mathematics or physics). In particular the application of quantum mechanics to chemistry is called quantum chemistry. Since the end of the second world war, the development of computers has allowed a systematic development of computational chemistry, which is the art of developing and applying computer programs for solving chemical problems. Theoretical chemistry has large overlap with molecular physics.

• Nuclear chemistry is the study of how subatomic particles come together and make nuclei. Modern Transmutation is a large component of nuclear chemistry, and the table of nuclides is an important result and tool for this field.

Other fields are Astrochemistry, Atmospheric chemistry, Chemical Engineering, Chemo-informatics, Electrochemistry, Environmental chemistry, Geochemistry, Green chemistry, History of chemistry, Materials science, Medicinal chemistry, Molecular Biology, Molecular genetics, Nanotechnology, Organometallic chemistry, Petrochemistry, Pharmacology, Photochemistry, Phytochemistry, Polymer chemistry, Supramolecular chemistry, Surface chemistry, and Thermochemistry.

Fundamental concepts

Nomenclature

Main article: IUPAC nomenclature

Nomenclature refers to the system for naming chemical compounds. There are well-defined systems in place for naming chemical species. Organic compounds are named according to the organic nomenclature system. Inorganic compounds are named according to the inorganic nomenclature system.

Atoms

Main article: Atom

An atom is a collection of matter consisting of a positively charged core (the atomic nucleus) which contains protons and neutrons, and which maintains a number of electrons to balance the positive charge in the nucleus.

Elements

Main article: Chemical element

An element is a class of atoms which have the same number of protons in the nucleus. This number is known as the atomic number of the element. For example, all atoms with 6 protons in their nuclei are atoms of the chemical element carbon, and all atoms with 92 protons in their nuclei are atoms of the element uranium.

The most convenient presentation of the elements is in the periodic table, which groups elements with similar chemical properties together. Lists of the elements by name, by symbol, and by atomic number are also available. In addition elements have many isotopes.

Compounds

Main article: Chemical compound

A compound is a substance with a fixed ratio of chemical elements which determines the composition, and a particular organization which determines chemical properties. For example, water is a compound containing hydrogen and oxygen in the ratio of two to one, with the Oxygen between the hydrogens, and an angle of 104.5° between them. Compounds are formed and interconverted by chemical reactions.

Molecules

Main article: Molecule

A molecule is the smallest indivisible portion of a pure compound or element that retains a set of unique chemical properties. A molecule consists of two or more atoms covalently bonded together.

Ions

Main article: Ion

An ion is a charged species, or an atom or a molecule that has lost or gained one or more electrons. Positively charged cations (e.g. sodium cation Na⁺) and negatively charged anions (e.g. chloride Cl^-) can form neutral salts (e.g. sodium chloride NaCl). Examples of polyatomic ions that do not split up during acid-base reactions are hydroxide (OH^-), or phosphate (PO₄^3-).

Substance

Main article: Chemical substance

A chemical substance can be an element, compound or a mixture of compounds, elements or compounds and elements. Most of the matter we encounter in our daily life are one or another kind of mixtures, e.g. air, alloys, biomass etc.

Bonding

Main article: Chemical bond

A chemical bond is an interaction which holds together atoms in molecules or crystals. In many simple compounds, valence bond theory and the concept of oxidation number can be used to predict molecular structure and composition. Similarly, theories from classical physics can be used to predict many ionic structures. With more complicated compounds, such as metal complexes, valence bond theory fails and alternative approaches which are based on quantum chemistry, such as molecular orbital theory, are necessary.

States of matter

Main article: Phase (matter)

A phase is a set of states of a chemical system that have similar bulk structural properties, over a range of conditions, such as pressure or temperature. Physical properties, such as density and refractive index tend to fall within values characteristic of the phase. The phase of matter is defined by the phase transition, which is when energy put into or taken out of the system goes into rearranging the structure of the system, instead of changing the bulk conditions.

Sometimes the distinction between phases can be continuous instead of having a discrete boundary, in this case the matter is considered to be in a supercritical state. When three states meet based on the conditions, it is known as a triple point and since this is invariant, it is a convenient way to define a set of conditions.

The most familiar examples of phases are solids, liquids, and gases. Less familiar phases include plasmas, Bose-Einstein condensates and fermionic condensates and the paramagnetic and ferromagnetic phases of magnetic materials. Even the familiar ice has many different phases, depending on the pressure and temperature of the system. While most familiar phases deal with three-dimensional systems, it is also possible to define analogs in two-dimensional systems, which is getting a lot of attention because of its relevance to biology.

Chemical reactions

Main article: Chemical reaction

Chemical reactions are transformations in the fine structure of molecules. Such reactions can result in molecules attaching to each other to form larger molecules, molecules breaking apart to form two or more smaller molecules, or rearrangement of atoms within or across molecules. Chemical reactions usually involve the making or breaking of chemical bonds.

Quantum chemistry

Main article: Quantum chemistry

Quantum chemistry describes the behavior of matter at the molecular scale. It is, in principle, possible to describe all chemical systems using this theory. In practice, only the simplest chemical systems may realistically be investigated in purely quantum mechanical terms, and approximations must be made for most practical purposes (e.g., Hartree-Fock, post Hartree-Fock or Density functional theory, see computational chemistry for more details). Hence a detailed understanding of quantum mechanics is not necessary for most chemistry, as the important implications of the theory (principally the orbital approximation) can be understood and applied in simpler terms.

Chemical Laws

Main article: Chemical law

The most fundamental concept in chemistry is the law of conservation of mass, which states that there is no detectable change in the quantity of matter during an ordinary chemical reaction. Modern physics shows that it is actually energy that is conserved, and that energy and mass are related; a concept which becomes important in nuclear chemistry. Conservation of energy leads to the important concepts of equilibrium, thermodynamics, and kinetics.

Further laws of chemistry elaborate on the law of conservation of mass. Joseph Proust’s law of definite composition says that pure chemicals are composed of elements in a definite formulation; we now know that the structural arrangement of these elements is also important.

Dalton’s law of multiple proportions says that these chemicals will present themselves in proportions that are small whole numbers (i.e. 1:2 O:H in water); although in many systems (notably biomacromolecules and minerals) the ratios tend to require large numbers, and are frequently represented as a fraction. Such compounds are known as non-stoichiometric compounds

Etymology

Main article: Etymology of chemistry

The Etymology of the word chemistry comes directly from the Greek word χημεια, and can be also met in the old French alkemie; or the Arabic al-kimia: the art of transformation.

See also

• List of chemists
• List of chemistry topics
• List of compounds
• List of important publications in chemistry
• Chemistry resources
• Unsolved problems in chemistry
• Perfection (“Perfection in physics and chemistry”)

External links

• MIT OpenCourseWare | Chemistry
• Wikidchem, The Free Chemistry Archive
• Chemical Glossary
• Chemistry Information Database
• Chemistry Forum
• IUPAC Nomenclature Home Page, see especially the “Gold Book” containing definitions of standard chemical terms
• Experiments videos and photos of the techniques and results
• More experiments - lots of information about the elements too.
• Material safety data sheets for a variety of chemicals
• Material Safety Data Sheets

Further reading

• Chang, Raymond. Chemistry 6th ed. Boston: James M. Smith, 1998. ISBN 0071152210.

Chemistry
Analytical chemistry | Biochemistry | Inorganic chemistry | Organic chemistry | Organometallic chemistry | Physical chemistry | Theoretical chemistry | Polymer chemistry | Chemical biology | Chemistry education | Materials science | Environmental chemistry | Green chemistry | Medicinal chemistry | Pharmacy | Pharmacology | Thermochemistry | Electrochemistry | Nuclear chemistry | Computational chemistry | Photochemistry
Periodic table | List of inorganic compounds | List of organic compounds | List of biomolecules

General subfields within the Natural sciences
Astronomy | Biology | Chemistry | Earth science | Ecology | Physical science | Physics

Chemistry resources

Chemistry resources is a collection of links and references that are useful for chemistry-related work. This includes free online chemical databases, publications, patents, computer programs, and various tools.

Contents 1 Free online resources 1.1 Databases 1.1.1 Substance and reaction data 1.1.2 References 1.1.3 Journals 1.2 Online tools 1.3 Nomenclature 1.4 Periodic tables 1.5 Software 1.6 Safety 1.6.1 Material Safety Data Sheets:MSDS 1.6.1.1 References 2 See also 3 External links

Free online resources

Databases

Substance and reaction data

• Organic Compounds Database Free compound search by structure
• Chemical catalog Compounds, analytical data
• Chmoogle The free chemistry search engine
• PubChem Compound, substance, and bioactivity data
• NCI Database Compound, substance, and bioactivity data, advanced search panel
• NIST Chemistry WebBook Compound data and spectra
• Chemical catalogue Compounds search engine
• Chemfinder Compound data (cookie-based accession limit)
• SDBS Spectra (UV/Vis, IR, NMR)
• Bordwell pKa Table pK_a values in DMSO
• Organic Synthesis Selected and commented reactions
• WebReactions Search for reactions
• Specialized Information Services (SIS) Division of the National Library of Medicine (NLM))
  • ChemIDplus Lite
  • ChemIDplus Advanced
• ChEBI - Chemical Entities of Biological Interest
• MSDChem (Ligand Chemistry) - Ligands, small molecules and monomers from PDB entries

See also: PubChem, Entrez, PubMed,GenBank, Chemical database, CAS registry number, List of inorganic compounds, List of organic compounds, List of biomolecules, List of minerals, Inorganic compounds by element, Dictionary of chemical formulas, PubMed,DOI, Patent, EPO, USPTO;

References

• PubMed Abstract database
• esp@cenet Patents
• USPTO Patents
• DOI Resolve Digital Object Identifiers (DOI)
• Chemical Databases

Journals

• Directory of Free Full-Text Journals in Chemistry

Online tools

• VCC-LAB logP, solubility, data format conversion, molecular descriptors
• PubChem online molecule editor that supports SMILES/SMARTS, InChI, and all common chemical file formats
• Daylight Depict SMILES to image converter
• CACTVS at NCI Structure to image converter
• Molinspiration Calculation of molecular descriptors and bioactivity score

See also: SMILES, InChI, Molecule editor;

Nomenclature

• IUPAC nomenclature

See also: IUPAC, IUPAC nomenclature ,List of pre-scientific substances, Wikipedia naming convention;

Periodic tables

• WebElements Periodic table

See also: Periodic table, List of elements by name, List of elements by symbol, List of elements by atomic number;

Software

• ChemDBsoft Structure drawing and storage
• OpenBabel File format interconversion
• JME molecule editor Molecule editor applet
• ACD/ChemSketch freeware
• ChemAxon Molecule editor applet and 2D/3D viewer (Marvin), database and complete cheminformatics toolkit (JChem) with API
• Jmol molecule viewer for SMILES
• Linux4Chemistry An extensive list of open source, freeware and commercial chemistry programs for Linux.

See also: SMILES, InChI, Molecule editor;

Safety

• Emergency Response Guidebook

Material Safety Data Sheets:MSDS

• Where to find MSDS on the Internet (very extensive)
• www.msdssearch.com
• SIRI MSDS index
• Cornell University MSDS index
• MSDS Authoring FAQ (Nexreg Compliance)
• MSDS FAQ (MSDSWriter)
• Sigma-Aldrich Risk and Safety Statements

References

• Reference catalog

See also: Hazardous material, Materials, NSC number, UN number, EINECS number, RTECS, Material safety data sheet, Risk and Safety Statements, List of R-phrases, List of S-phrases;

See also

• Portal:Chemistry Wikipedia chemistry portal

External links

• CHIN list of chemical databases
• NIH list of resources
• ESIS (European chemical Substances Information System)
• Chemistry at Sutton College
• Chemical Engineering Resources
• ENVIRONMENTAL HEALTH & SAFETY RESOURCES

Chemurgy

Chemurgy is a branch of applied chemistry that is concerned with preparing industrial products from agricultural raw materials. Popular during the Second World War, only within the last 20 years has interest in this field once again begun to revive. A prime example is the search for organic replacements for petroleum-based oil and gas (see biodiesel) and new food plants.

Substitutions

• Kenaf for jute (rope)
• castor oil for petroleum-based oil (lubrication)

New foods

Clandestine chemistry

Clandestine chemistry generally refers to chemistry carried out in illegal drug laboratories, but can include any kind of laboratory operation carried on in secret because of the illegality of its activities. It is important to distinguish between large and small scale clandestine labs. Some individual chemists work clandestinely in order to synthesize controlled substances for their own use in order to guarantee purity and quality.

Contents 1 History 2 Precursor chemicals 3 Leading suppliers of precursor chemicals 4 Enforcement of controls on precursor chemicals 5 Amphetamines 6 Modern 7 See also

History

Ancient forms of clandestine chemistry included the manufacturing of poisons.

Another old form of clandestine chemistry is the illegal brewing and distillation of alcohol. This was frequently done to avoid taxation on spirits.

In the United States in the 1920s, alcohol was on prohibition. This opened a door for brewers to supply their own town with alcohol. Just like modern day drug labs, distilleries were placed in rural areas. The term moonshine generally referred to “corn whiskey”, that is, a whiskey-like liquor made from corn.

Precursor chemicals

With the exception of cannabis, and other herbal plants (like kava kava, salvia divinorum) every illicit drug requires chemicals to be refined to its final, consumable form (e.g. the coca plant to cocaine, the poppy plant to morphine), or is purely the result of chemical synthesis (e.g. methamphetamine, ecstasy, etc). Governments have adopted a strategy of chemical control as part of their overall drug control and enforcement plans. Chemical control offers a means of attacking illicit drug production and disrupting the process before the drugs have entered the market.

Because many legitimate industrial chemicals are also necessary in the processing and synthesis of most illicitly produced drugs, preventing the diversion of these chemicals from legitimate commerce to illicit drug manufacturing is a difficult job. Further, since so many chemicals listed as illicit drug precursors are manufactured all over the world, international cooperation combined with a comprehensive chemical control strategy is essential for chemical control policies to succeed.

Leading suppliers of precursor chemicals

Chemicals critical to the production of cocaine, heroin, and synthetic drugs are produced in many countries throughout the world. Many manufacturers and suppliers exist in Europe, China, India, the United States, and a host of other countries.

Historically, chemicals critical to the synthesis or manufacture of illicit drugs are introduced into various venues via legitimate purchases by companies that are registered and licensed to do business as chemical importers or handlers. Once in a country or state, the chemicals are diverted by rogue importers or chemical companies, by criminal organizations and individual violators, or, more typically seen in an overseas environment, acquired as a result of coercion on the part of drug traffickers. In response to stricter international controls, drug traffickers have increasingly been forced to divert chemicals by mislabeling the containers, forging documents, establishing front companies, using circuitous routing, hijacking shipments, bribing officials, or smuggling products across international borders.

Enforcement of controls on precursor chemicals

Operation Purple is a U.S. DEA driven international chemical control initiative designed to reduce the illicit manufacture of cocaine in the Andean Region by monitoring and tracking shipments of potassium permanganate (PP), the chemical oxidizer of choice for cocaine production. The cornerstone of the operation is an intensive PP tracking program aimed at identifying and intercepting diverted potassium permanganate; identifying rogue firms and suspect individuals; gathering intelligence on diversion methods, trafficking trends, and shipping routes; and taking administrative, civil, and/or criminal action as appropriate. Critical to the success of this operation is the communication network that gives notification of shipments and provides the government of the importer sufficient time to verify the legitimacy of the transaction and take appropriate action. The effects of this initiative have been dramatic and far-reaching. Operation Purple has exposed a significant vulnerability among traffickers, and has grown to include almost thirty nations. According to the DEA, Operation Purple has been highly effective at interfering with cocaine production.

Acetic anhydride (AA), the most commonly used chemical agent in heroin processing, is virtually irreplaceable. According to the DEA, Mexico remains the only heroin source country that has indigenous acetic anhydride production capability, producing 87,000 metric tons in 1999 alone. All other heroin producing countries must import large amounts of acetic anhydride. The diversion of this chemical to Colombian heroin laboratories is a continuing problem. The DEA reports that in 1999 three major hijackings of tanker trucks containing acetic anhydride occurred in Colombia. A total of 95.9 metric tons of AA was stolen, an amount sufficient to supply the Colombian heroin trade for the next five years. However, the largest markets for diverted acetic anhydride continue to be heroin laboratories in Afghanistan and Burma. Of particular note was a March 2000 seizure of 72.8 metric tons of AA in Turkmenistan, en route to heroin laboratories in Afghanistan. Authorities in Uzbekistan, Turkmenistan, Kyrgyzstan, and Kazakhstan routinely seize ton quantity shipments of diverted acetic anhydride.

DEA’s Operation Topaz is a coordinated international strategy targeting acetic anhydride. In place since March 2001, a total of thirty-one countries are currently organized participants in the program in addition to regional participants. The DEA reports that as of June 2001, some 125 consignments of acetic anhydride had been tracked totaling 61,890,222.85 kilograms. As of July 2001, there has been approximately 20 shipments of AA totaling 185,000 kilograms either stopped or seized.

The methamphetamine situation changed in the mid-1990’s with the entrance of Mexican organized crime into production and distribution. According to the DEA, the seizure of 3.5 metric tons of pseudoephedrine (the primary precursor chemical used in the production of methamphetamine) in Texas revealed that Mexican trafficking groups were producing methamphetamine on an unprecedented scale, with potentially serious repercussions for drug abuse throughout the United States.

In countries where strict chemical controls have been put in place, illicit drug production has been seriously affected. For example, few of the chemicals needed to process coca leaf into cocaine are manufactured in Bolivia or Peru. Most are smuggled in from neighboring countries with advanced chemical industries or diverted from a smaller number of licit handlers. Increased interdiction of chemicals in Peru and Bolivia has contributed to final product cocaine from those countries being of lower, minimally oxidized quality.

As a result, Bolivian lab operators are now using inferior substitutes such as cement instead of lime and sodium bicarbonate instead of ammonia, recycled solvents like ether, and are attempting to streamline a production process that virtually eliminates oxidation to produce cocaine base. Some laboratories are not using sulfuric acid during the maceration state; consequently, less cocaine alkaloid is extracted from the leaf, producing less cocaine hydrochloride, the powdered cocaine marketed in the United States. Similarly, heroin-producing countries depend on supplies of acetic anhydride from the international market. This heroin precursor continues to account for the largest volume of internationally seized chemicals, according to the International Narcotics Control Board. Since July 1999, there have been several notable seizures of acetic anhydride in Turkey (amounting to nearly seventeen metric tons) and Turkmenistan (totaling seventy-three metric tons).

The Multilateral Chemical Reporting Initiative encourages governments to exchange information on a voluntary basis in order to monitor international chemical shipments. Over the past decade, key international bodies like the Commission on Narcotic Drugs and the U.N. General Assembly’s Special Session (UNGASS) have addressed the issue of chemical diversion in conjunction with U.S. efforts. These organizations raised specific concerns about potassium permanganate and acetic anhydride.

To facilitate the international flow of information about precursor chemicals, the United States, through its relationship with the Inter-American Drug Control Abuse Commission (CICAD), continues to evaluate the use of precursor chemicals and assist countries in strengthening controls. Many nations still lack the capacity to determine whether the import or export of precursor chemicals is related to legitimate needs or illicit drugs. The problem is complicated by the fact that many chemical shipments are either brokered or transshipped through third countries in an attempt to disguise their purpose or destination.

The International Narcotics Control Board (INCB) has opted to organize an international conference with the goal of devising a specific action plan to counter the traffic in MDMA precursor chemicals. In July 2001, the INCB requested the assistance of DEA in planning an international conference on preventing the diversion of chemicals used in the production of amphetamine-type stimulants (ATS), including ecstasy (MDMA) and methamphetamine.

Despite this long history of law enforcement actions, restrictions of chemicals, and even covert military actions, it must be noted that in the United States most illicit drugs are as or more available, purer, and less expensive than at any time since drug prohibition was imposed in the early 20th century.

Amphetamines

Clandestine chemistry made its mark in the late 1960s when amphetamines became illegal. Biker gangs including the Hell’s Angels took control over the manufacture of amphetamines using standard laboratory equipment.

Methamphetamine was a favorite among biker gangs. But after phenylacetone became a Schedule II controlled immediate precursor in 1979, it was harder for underground chemists to manufacture methamphetamine.

Frustrated, underground chemists searched for alternative methods for producing methamphetamine, and figured out how to convert ephedrine into methamphetamine. At the time, ephedrine was not a watched chemical, and ephedrine pills could be bought by the thousands without raising any kind of suspicion.

In the 1990s, ephedrine became a closely watched chemical by the DEA, effectively making it harder for underground chemists to produce methamphetamine.

In 2002, there were over 15,000 methamphetamine lab busts, mostly in poor areas of the West and Midwest.

Modern

Clandestine chemistry does not limit itself only to drugs, it is also associated with explosives, and other illegal chemicals. Nitroglycerin is one chemical that clandestine chemists are known for producing on a small scale. Other, simpler explosives are commonly made by people for “fun”, including acetone peroxide.

Uncle Fester is a writer who commonly writes about different aspects of clandestine chemistry. Secrets of Methamphetamine Manufacture is among one of his most popular books, and is considered required reading for DEA Agents. More of his books deal with other aspects of clandestine chemistry, including explosives, and poisons. Fester is, however, considered by many to be a faulty and unreliable source for information in regard to the clandestine manufacture of chemicals.

Alexander Shulgin and his wife Ann Shulgin wrote two extremely important volumes to the world of illicit chemistry entitled TiHKAL and PiHKAL. Their research has been of paramount importance to the clandestine world. It should be stressed that their work with a degree in chemistry along with the proper government permissions is the only sure way to study illicit chemicals safely.

Other forms of clandestine chemistry have gained popularity among some teenagers. Since the rise of the Internet, some teenagers have access to information on topics such as the extraction of dextromethorphan (DXM) from over the counter cough medicine. Some teenagers have also gained knowledge regarding the manufacturing of explosives, the most popular of which is acetone peroxide. But due to the lack of reliable information on the Internet, deaths have occurred in a small number of these amateur chemistry experiments.

See also

• Over the counter

Cis-acting

A molecule may be described as cis-acting when it affects other entities only if they are physically adjacent. It may be considered ‘the opposite’ of a ‘trans-acting’ molecule.

It is common to describe transcription factors as either cis or trans-acting. A cis-acting transcription promoter facilitates the transcription of adjacent polypeptide-encoding sequences whereas trans-acting promoters affect the transription of regions of DNA not in close physical proximity.

Classes of metals

Class A metals are metals that form hard acids. Hard acids are acids with relatively ionic bonds. These metals, such as iron, aluminum, titanium, sodium, calcium and the lanthanides, would rather bond with fluorine than iodine. They form stable products with hard bases, which are bases with ionic bonds.

Class B metals are metals that form soft acids. Soft acids are acids with relatively covalent bonds. These metals, such as lead, gold, palladium, platinum, mercury and rhodium, would rather bond with iodine than fluorine. They form stable products with soft bases, which are bases with covalent bonds.