Biology · Fundamental Principles of Organic Chemistry

Functional group isomerism is demonstrated by C₆H₅C≡N (benzonitrile) and C₆H₅N≡C (phenyl isocyanide) because they have the same molecular formula but different functional groups due to the distinct arrangement of the carbon-nitrogen triple bond. This arrangement leads to different chemical properties and reactivity.

Other types of isomerism such as optical, skeletal, and metamerism are not applicable here because they involve different structural or stereochemical differences, or different arrangements of alkyl groups, which are not present in this case.

Functional group isomerism occurs when compounds with the same molecular formula have different functional groups. Here, the compounds differ in the arrangement of the carbon-nitrogen triple bond, classifying them as functional group isomers.

Optical isomerism involves isomers that differ in the way they rotate plane-polarized light due to the presence of chiral centers. This type of isomerism is not applicable here as there are no chiral centers in the given compounds.

Skeletal isomerism involves compounds with the same molecular formula but different arrangements of the carbon skeleton. The given compounds differ in functional groups, not skeletal structures.

Metamerism is a type of isomerism where compounds have the same molecular formula but differ in the alkyl chains on either side of a functional group. This is not applicable here as the difference lies in the functional group itself, not the side chains.