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A way of denoting the absolute structure of an optical isomer (see optical activity). Two conventions are in use: The ...

A chemical reaction that involves bimolecular removal of an atom or ion from a molecule. An example is the abstraction of hydrogen from methane by reaction with a radical:...

A colourless crystalline aromatic compound, C₁₂H₁₀; m.p. 95°C; b.p. 278°C. It is an intermediate in the production of some dyes....

Organic compounds formed by addition of alcohol molecules to aldehyde molecules. If one molecule of aldehyde (RCHO) reacts with one molecule of alcohol (R...

A substance that is released at some (cholinergic) nerve endings. Its function is to pass on a nerve impulse to the next nerve (i.e. at a synapse) or to initiate muscular contraction. Once acetylcholine has been released, it has only a transitory effect because it is rapidly broken down by the enzyme ...

1. A type of compound that contains hydrogen and dissociates in water to produce positive hydrogen ions. The reaction, for an acid HX, is commonly written:...

Compounds that react with water to form an acid. For example, carbon dioxide reacts with water to give carbonic acid:...

A hydrogen atom in an *acid that forms a positive ion when the acid dissociates. For instance, in methanoic acid...

A colourless crystalline heterocyclic compound, C₁₂H₉N; m.p. 110°C. The ring structure is similar to that of anthracene, with three fused rings, the centre ring containing a nitrogen hetero atom. Several derivatives of acridine (such as acridine orange) are used as dyes or biological stains....

The minimum energy required for a chemical reaction to take place. In a reaction, the reactant molecules come together and chemical bonds are stretched, broken, and formed in producing the products. During this process the energy of the system increases to a maximum, then decreases to the energy of the products (see illustration). The activation energy is the difference between the maximum energy and the energy of the reactants; i.e. it is the energy barrier that has to be overcome for the reaction to proceed. The activation energy determines the way in which the rate of the reaction varies with temperature (...

1. Symbol a. A thermodynamic function used in place of concentration in equilibrium constants for reactions involving nonideal gases and solutions. For example, in a reaction...

The process of introducing an acyl group (RCO–) into a compound. The usual method is to react an alcohol with an acyl halide or a carboxylic acid anhydride; e.g....

A colourless crystalline hydrocarbon C₁₀H₁₆; m.p. 269°C. It is found in certain petroleum fractions. The structure contains three symmetrically fused cyclohexane rings....

A chemical reaction in which one molecule adds to another. Addition reactions occur with unsaturated compounds containing double or triple bonds, and may be ...

A *purine derivative. It is one of the major component bases of *nucleotides and the nucleic acids *...

A nucleoside comprising one adenine molecule linked to a d-ribose sugar molecule. The phosphate-ester derivatives of adenosine, AMP, ADP, and ...

A hormone, produced by the medulla of the adrenal glands, that increases heart activity, improves the power and prolongs the action of muscles, and increases the rate and depth of breathing to prepare the body for ‘fright, flight, or fight’. At the same time it inhibits digestion and excretion....

A type of indicator used in reactions that involve precipitation. The yellow dye fluorescein is a common example, used for the reaction...

A poisonous compound, C₁₅H₁₂O₆, produced by the fungus Aspergillus flavus. It is extremely toxic to farm animals and can cause liver cancer in humans. It may occur as a contaminant of stored cereal crops, cotton seed, and, especially, peanuts. There are four isomeric forms....

Organic compounds that contain the –OH group. In systematic chemical nomenclature alcohol names end in the suffix -ol. Examples are methanol, CH...