To identify which of the given molecules is a secondary amine, let's first understand what a secondary amine is. An amine is classified based on the number of alkyl or aryl groups attached to the nitrogen atom:
1. Primary Amine: One alkyl or aryl group attached to the nitrogen (R-NH₂).
2. Secondary Amine: Two alkyl or aryl groups attached to the nitrogen (R-NH-R').
3. Tertiary Amine: Three alkyl or aryl groups attached to the nitrogen (R-NR'-R'').
4. Ammonia: No carbon groups attached to the nitrogen (NH₃), which is not an amine.
We will now examine each molecule to determine its classification:
1. [tex]\( CH _3 CH _2 NH _2 \)[/tex]:
- Structure: Ethylamine
- Contains one ethyl group attached to the nitrogen
- Classification: Primary amine
2. [tex]\( CH _3 CH _2 NHCH _3 \)[/tex]:
- Structure: Ethylmethylamine
- Contains one ethyl group and one methyl group attached to the nitrogen
- Classification: Secondary amine
3. [tex]\( \left( CH _3 CH _2 \right)_3 N \)[/tex]:
- Structure: Triethylamine
- Contains three ethyl groups attached to the nitrogen
- Classification: Tertiary amine
4. [tex]\( NH _3 \)[/tex]:
- Structure: Ammonia
- Contains no carbon groups attached to the nitrogen
- Classification: Ammonia (not an amine)
Therefore, among the given options, [tex]\( CH _3 CH _2 NHCH _3 \)[/tex] is identified as the secondary amine.
So, the secondary amine is the second molecule, i.e., [tex]\( CH _3 CH _2 NHCH _3 \)[/tex], which corresponds to the index 2 when considering a zero-based indexing system.
