Chapter 18: Further Organic Chemistry Glossary

Worksheet 18.1

Chapter 18: Further organic chemistry – glossary

Acid anhydride An organic molecule with the formula RCOOCOR; a derivative of carboxylic acids.

Acylating agents A reagent that is able to introduce an acyl group (R–C = O) into an organic molecule. Examples include acyl chlorides and acid anhydrides.

Acyl chloride An organic molecule with the formula RCO; a derivative of a carboxylic acid in which the –OH group has been replaced by –Cl.

Acyl group The R–C = O group. It is found in all derivatives of carboxylic acids, including esters, amides, acyl chlorides and acid anhydrides.

Addition–elimination reaction A reaction in which two molecules combine with the release of a small molecule, often water. This type of reaction is also known as condensation.

Addition reaction A reaction in which two reactants combine to form a single product. This type of reaction is typical of unsaturated compounds.

Aliphatic An organic compound that is not based on a benzene ring.

Alkylation A reaction in which an alkyl group (-CH3, -C2H5, etc.) replaces a hydrogen atom.

Arene An organic compound that is derived from benzene C6H6. These compounds are also described as being aromatic.

Benzene ring The cloud of delocalized p electrons in benzene, C6H6. This stabilizes the molecule, giving it unique properties due to its high resonance energy.

Carbocation A species formed as an intermediate during a reaction that has a positive charge on a carbon atom. Tertiary carbocations are more stable than secondary, which are more stable than primary, due to the positive inductive effect of the alkyl groups.

Carbonyl group The C = O group, present in aldehydes, ketones, carboxylic acids and their derivatives.

Condensation A reaction in which two molecules combine with the release of a small molecule, often water. This type of reaction is also known as addition–elimination.

Conjugation Delocalisation of electrons from two p bonds separated by a single bond, or from a lone pair adjacent to a benzene ring.

Dehydration An elimination reaction in which the small molecule lost is water.

Electrophile An electron-deficient species that is attracted to parts of molecules that are electron rich. Electrophiles are positive ions or have a partial positive charge.

Electrophilic addition An addition reaction in which an electrophile attacks an electron-rich species, leading to breakage of the p bond in a C = C double bond. It is characteristic of alkenes.

Electrophilic substitution A substitution reaction in which an electrophile attacks an electron-rich species, and replaces a bonded group. It is characteristic of arenes.

Elimination A type of reaction in which a small molecule is lost from a larger compound. The reaction will produce an unsaturated product.

Friedel–Crafts reaction A type of reaction in which an alkyl or acyl group is substituted into an arene. They are an important way of establishing carbon side chains in benzene and its derivatives.

Grignard reagent Organometallic compounds with the formula R-Mg-X, where X is a halogen. They are used for extending the length of the carbon chain in reaction pathways.

Halogen carrier catalyst An electron-deficient species, such as AlCl3, that acts as a Lewis acid, accepting a lone pair of electrons from a halogen and so inducing polarity. It is used to generate electrophiles from halogens, for substitution into arenes. It is also used in Friedel-Crafts reactions to generate electrophiles from acyl chlorides or from halogenoalkanes.

Heterolytic fission When a covalent bond breaks in a reaction and both the bonded electrons go to one of the products, so giving rise to two oppositely charged ions.

Leaving group An atom or group of atoms that is displaced during a substitution or an elimination reaction.

Markovnikov’s rule When an unsymmetrical reagent adds to an unsymmetrical alkene, the electrophilic portion of the reagent adds to the carbon that is bonded to the greater number of hydrogen atoms.

Nitrating mixture A mixture of concentrated nitric and sulfuric acids, which generates the active species –NO2 +, the nitronium ion. It is used in the nitration of benzene.

Nucleophile An electron-rich species which is attracted to parts of a molecule that are electron deficient. Nucleophiles possess one or more lone pairs of electrons and may also carry a negative charge.

Nucleophilic addition An addition reaction in which a nucleophile attacks an electron-deficient species, leading to breakage of a double bond. It is characteristic of the carbonyl group, C = O.

Positive inductive effect The tendency of an atom or group to push electrons away from itself. These groups, such as alkyl groups, are also known as electron-releasing groups.

Primary carbocation A carbocation which is attached to at least two hydrogen atoms.

Reflux A technique used during heating, to prolong a reaction when the products may be volatile and escape before they have time to react completely. The apparatus consists of a vertical distillation column, which allows escaping vapour to be condensed and returned to the reaction vessel.

Resonance energy for benzene The lowering of benzene’s internal energy as a result of its delocalized p electron cloud. This energy has to be overcome if the benzene ring is to be broken, which is why benzene is reluctant to undergo addition reactions.

Ring activators Substituent groups in benzene, such as –CH3 and –OH, that increase the reactivity of the ring towards further electrophilic substitution. They direct incoming groups to the 2 and 4 positions in the ring.

Ring deactivators Substituent groups in benzene, such as –NO2, that decrease the reactivity of the ring towards further electrophilic substitution. They direct incoming groups to the 3 position.

Secondary carbocation A carbocation which is attached to one hydrogen atom.

Tertiary carbocation A carbocation which is not attached to any hydrogen atoms.

2,4-dinitrophenylhydrazine (2,4-DNP) A compound which undergoes addition–elimination reaction with aldehydes and ketones to form 2,4-dinitrophenylhydrazone. It is used in characterization of aldehydes and ketones through melting point determination of the condensation product.