Question

Which of the following is an example of symmetrical tertiary amine?

• A.

  

• B.

  

• C.

  

• D.

  

Hint:

For an amine to be called a "symmetrical tertiary" amine, its name must follow the pattern "Tri[alkyl]amine" (e.g., trimethylamine, triethylamine). This indicates that three identical alkyl pathways are bonded to the central nitrogen.

Answer 1

The Correct Option is A

Step 1: Recall what symmetrical and tertiary mean.
A tertiary ($3^\circ$) amine has nitrogen bonded to three carbon groups and no $N-H$ bond. Symmetrical means all three groups are identical.
Step 2: Write the general formula.
A symmetrical tertiary amine is $R_3N$ where $R$ is the same group three times, for example $N(CH_3)_3$.
Step 3: Count groups on nitrogen, not hydrogens.
Instead of memorising structures, just ask how many carbons touch nitrogen. Three carbons and zero $N-H$ means tertiary.
Step 4: Eliminate using the $N-H$ test.
Dimethylamine $(CH_3)_2NH$, ethylmethylamine $CH_3-NH-C_2H_5$ and diethylamine $(C_2H_5)_2NH$ each still keep one $N-H$ bond, so they are secondary, not tertiary. We discard all three.
Step 5: Check symmetry of the survivor.
Only trimethylamine $N(CH_3)_3$ has three carbon groups on nitrogen. All three are methyl, so the three arms are identical and the molecule is symmetrical.
Step 6: State the result.
The compound that is both tertiary and symmetrical is trimethylamine, which is option (A).
\[ \boxed{\text{Trimethylamine, } N(CH_3)_3 \text{ (option A)}} \]