Aniline vs Benzylamine

[DeathandTaxes]

---

Members don't see this ad.

I came across a question that asked us to identify what they had in common.

A. Primary Amine
B. Conjugated Amine
C. Aromatic Amine
D. Nonalkyl Amine

I thought it was Aromatic because they were both attached to a benzene ring (which is aromatic). I was on the fence between that and Conjugated Amine, because aromatic rings are also conjugated. It turned out neither was right. Could someone explain to me the difference between aromaticity/conjugation, and how these two structures differ in this regard?

 

[1bls2g]

answer should be A but I'm not 100% caught up on orgo so I won't give any explanation to avoid misleading you by accident.

 

[DeathandTaxes]

I know the answer is A, my main difficulty was knowing why B and C are wrong.

 

[JMMTB]

The first thing to note is that benzylamine is not conjugated with the Benzene ring. In between the nitrogen and the benzene is a sp3 Carbon. It would be impossible to draw resonance structures involving the nitrogen and the benzene ring because of that carbon between them. In order for something to be conjugated there must be continuous p orbitals. This allows a continuous flow of electron density. Aniline is conjugated with the benzene ring because the nitrogen is sp2 hybridized with the lone pair in a p orbital.

For something to be aromatic there are four rules
1. huckels rule: # electrons in pi system =4n +2 where n is any integer 0,1,2,3...
2.Cyclic
3.Full conjugated (continuous p orbitals)
4.Planar

The amine group of benzylamine can thus not be conjugated with the benzene nor aromatic. This eliminates choices B and C. The amine obviously has an alkyl group which eliminates D.

A is thus the correct answer as each of the amines are primary.

 

[dudewheresmymd]

I came across a question that asked us to identify what they had in common.

A. Primary Amine
B. Conjugated Amine
C. Aromatic Amine
D. Nonalkyl Amine

I thought it was Aromatic because they were both attached to a benzene ring (which is aromatic). I was on the fence between that and Conjugated Amine, because aromatic rings are also conjugated. It turned out neither was right. Could someone explain to me the difference between aromaticity/conjugation, and how these two structures differ in this regard?

This is an AAMC question should be posted in the proper thread.

 

[DeathandTaxes]

I came across this in TBR actually. But you're right in that a similar question is on the AAMC practice exam.

 

[dudewheresmymd]

I came across this in TBR actually. But you're right in that a similar question is on the AAMC practice exam.

Ah okay. TBR giving away questions now.