Reactions of Functional Groups

Reactions of Functional Groups

Reactivity of Functional Groups

  • Functional groups strongly influence the reactivity of a molecule and its behavioural pattern in a chemical reaction.
  • Each functional group has a characteristic set of reactivity based on the atom, or atoms, that form the group.
  • The direction and rate of chemical reactions involving organic compounds can often be predicted by considering the functional groups present.

Hydroxyl Groups (-OH)

  • Hydroxyl groups are found in alcohols, and their reactivity is characterized by the replacement of the hydrogen atom or the -OH group altogether.
  • In substitution reactions, another atom or group replaces the hydroxyl hydrogen. For example, Na replaces the H in ethanol during a substitution reaction to form sodium ethoxide.
  • In elimination reactions, alcohols can lose the -OH group to form alkenes with a catalyst and other conditions.

Carbonyl Groups (>C=O)

  • The carbonyl group is found in aldehydes, ketones, and carboxylic acids. The reactivity is due to the polarity of the bond.
  • Aldehydes and ketones are most reactive towards nucleophiles in nucleophilic addition reactions. For example, with H-CN, they produce cyanohydrins.
  • Carboxylic acids react with metals, bases, and carbonates in acid-base reactions to produce salts, often with evolution of gas.

Carboxyl Groups (-COOH)

  • The carboxyl group found in carboxylic acids can lose a proton (H+) in the presence of a base which results in a carboxylate ion. This is the behavior of an acid, thus its name.
  • Carboxylic acids also undergo esterification with alcohols to form esters in the presence of a catalyst.

Amino Groups (-NH2)

  • The amino group is a functional group that consists of a nitrogen atom attached by single bonds to hydrogen atoms. When attached to a carbon atom, it forms compounds called amines.
  • Primary amines react with nitrous acid to yield a diazonium salt.
  • Amines also react with carboxylic acids to form amides in a process known as amide linkage.

Understanding how these functional groups react can form a firm base for understanding the complexity of organic chemistry and provide insight into the construction of many natural and synthetic products.