JEE Main 2021 · 27 July · morning · Numerical answer · +4 / −0
In gaseous triethyl amine the "-C-N-C-" bond angle is _________ degree.
Answer and solution
Answer 108
Solution
Chemistry ma’am · 4 steps
Start at 109.5°: the lone pair squeezes the angle, and the bulky ethyl groups push it back open.
- Shape at nitrogen. Nitrogen in an amine is sp³ hybridised. Three orbitals bond to carbon and the fourth holds a lone pair, so the molecule is pyramidal.
- Lone pair squeezes. A lone pair repels more strongly than a bond pair. It pushes the three C-N bonds closer together, so the angle drops below the tetrahedral 109.5°. In NH₃ it falls to about 107°.
- Alkyl groups push back. Ethyl groups are much bulkier than hydrogen atoms. Their steric repulsion opens the angle up again, so it ends up a little larger than in ammonia but still below 109.5°.
- So. The C-N-C bond angle in gaseous triethylamine is about 108 degrees.
The idea to keep. In amines, the lone pair squeezes the angle below 109.5° while bulky alkyl groups widen it. So alkylamines sit near 108°, just above ammonia's 107°.
Answer from the NTA final answer key. Solution by PrepWiser.