Chemical Identity: Functional Group Isomerism Quiz

Compounds with one degree of unsaturation and one oxygen, such as C3H6O, can exist as either an aldehyde (propanal) or a ketone (propanone). These are classic functional isomers.

Both have the formula C2H6O. However, Ethanol has an OH group (alcohol), while Dimethyl Ether has a COC linkage (ether). This change in connectivity results in Ethanol having a much higher boiling point due to hydrogen bonding.

Carboxylic acids and esters are functional isomers. For the formula C2H4O2, Ethanoic acid is the acid form, and Methyl formate is the corresponding ester.

Alkenes and cycloalkanes share the same general formula CnH2n (one degree of unsaturation). For example, Propene and Cyclopropane are functional isomers.

While all are amines, the connectivity of the nitrogen (attached to 1, 2, or 3 carbons) changes the functional nature of the molecule, affecting its hydrogen bonding capacity.

These are position isomers, not functional isomers. They both belong to the same functional class (alcohols); they only differ in the location of the hydroxyl group on the carbon chain.

Both alkynes and cycloalkenes have two degrees of unsaturation. For C3H4, you could have Propyne (triple bond) or Cyclopropene (one ring and one double bond).

Propanal/Propanone (Aldehyde/Ketone), Benzyl alcohol/Anisole (Alcohol/Ether), and Ethanoic acid/Methyl formate (Acid/Ester) all have different functional groups. Pent-1-yne and Pent-2-yne are position isomers.

Amides contain a carbonyl group and a nitrogen. A simple amine lacks the oxygen atom entirely, so they cannot be isomers unless the amine contains an additional oxygen-bearing group.

In nitroalkanes, the carbon is bonded to Nitrogen. In alkyl nitrites, the carbon is bonded to Oxygen. This change in connectivity defines them as functional isomers.

Cyanides (R-CN) and Isocyanides (R-NC) share the same molecular formula but differ in which atom (C or N) is attached to the alkyl group.

This formula allows for a carboxylic acid, different esters, or a molecule containing both an alcohol and an aldehyde group.

Propan-1-ol is an alcohol, which allows for extensive intermolecular hydrogen bonding. Its functional isomer, Ethyl methyl ether, cannot hydrogen bond with itself, leading to a much lower boiling point.

For the formula C7H8O, Cresol (a methyl-phenol) and Anisole (methoxybenzene) are functional isomers. One contains a hydroxyl group, while the other contains an ether linkage.

Both a ring and a double bond count as one degree of unsaturation each (total of 2). An alkyne also has two degrees of unsaturation (two pi bonds), making them potential functional isomers.