S3.2 Functional groups: Classification of organic compounds

An N-substituted amide contains the amide functional group ($-\text{CONH}-$) where the nitrogen atom carries at least one alkyl (or aryl) substituent rather than two hydrogen atoms as in a primary amide ($-{\text{CONH}}_2$).

The key feature is a carbonyl carbon ($\text{C}=\text{O}$) bonded directly to a nitrogen atom that also bears a carbon substituent. In ${\text{CH}}_3{\text{CH}}_2{\text{NHCOCH}}_3$, the nitrogen is bonded to an ethyl group AND to a carbonyl carbon, making this an N-ethyl substituted amide.

${\text{CH}}_3{\text{CH}}_2{\text{NHCOCH}}_3$ contains the $-\text{CO}-\text{NH}-$ linkage with an alkyl group on nitrogen. This is correctly classified as an N-substituted amide (specifically N-ethylethanamide).

The correct answer is ${\text{CH}}_3{\text{CH}}_2{\text{NHCOCH}}_3$.

We need to find the structure that represents an N-substituted amide — an amide where the nitrogen has an alkyl group attached instead of (or in addition to) hydrogen.

${\text{CH}}_3{\text{CONH}}_2$ is ethanamide, a primary amide — the nitrogen has two hydrogen atoms and no alkyl substituent. This is not N-substituted.

${\text{CH}}_3{\text{CH}}_2{\text{NH}}_2$ is ethylamine, a primary amine. There is no carbonyl group adjacent to the nitrogen, so this is not an amide at all.

${\text{CH}}_3\text{CONHOH}$ is a hydroxamic acid, where the substituent on nitrogen is an $-\text{OH}$ group, not a carbon alkyl group. This does not fit the definition of an N-substituted amide in the context of IB chemistry.

${\text{CH}}_3{\text{CH}}_2{\text{NHCOCH}}_3$ contains a carbonyl bonded to nitrogen ($-\text{CONH}-$) with an ethyl group on the nitrogen. This is an N-substituted amide.

In ${\text{CH}}_3{\text{CH}}_2{\text{COCH}}_2{\text{CH}}_2{\text{NH}}_2$, the $\text{C}=\text{O}$ group is positioned between two carbon atoms (ethyl on one side, $-{\text{CH}}_2-$ on the other). A carbonyl group within the carbon chain, not at the terminal position, identifies a ketone.

The $-{\text{NH}}_2$ group at the end of the chain is bonded only to carbon atoms, not adjacent to a carbonyl. This is a primary amine, not an amide.

An amide requires the nitrogen to be directly bonded to a carbonyl carbon ($-\text{CO}-{\text{NH}}_2$ or $-\text{CONH}-$). Here, the $-{\text{NH}}_2$ and $\text{C}=\text{O}$ are separated by two ${\text{CH}}_2$ groups, so they are independent functional groups: a ketone and an amine.

The molecule contains a ketone (mid-chain $\text{C}=\text{O}$) and an amine ($-{\text{NH}}_2$). The correct answer is Ketone and amine.

We need to identify both functional groups in ${\text{CH}}_3{\text{CH}}_2{\text{COCH}}_2{\text{CH}}_2{\text{NH}}_2$ by examining the arrangement of atoms.

An aldehyde requires $-\text{CHO}$ at the end of a chain. The carbonyl here is between two carbon groups (mid-chain), so it is a ketone, not an aldehyde. This option is incorrect.

A carboxylic acid requires $-\text{COOH}$; an amide requires $-{\text{CONH}}_2$ or $-\text{CONH}-$. Neither group is present here — there is no $-\text{OH}$ on the carbonyl, and the $-{\text{NH}}_2$ is not adjacent to $\text{C}=\text{O}$. This option is incorrect.

Although a ketone is correctly identified, the nitrogen group is not an amide because the $-{\text{NH}}_2$ is two carbons away from the carbonyl. An amide requires direct $\text{C}=\text{O}$—$\text{N}$ bonding.

The mid-chain $\text{C}=\text{O}$ is a ketone, and the terminal $-{\text{NH}}_2$ is an amine. The correct answer is Ketone and amine.