2 Orgo Questions from EK10001

[sexycani]

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#33: Basically, is an immine group considered an amine functionality?

(the question has a compound with 6 amine groups and 6 immines and it asks for the number of amine functionalities present)

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#465: Dehydration of 2-hexanol to form 2-hexene and 1-hexene proceeds by what mechanism?

A. Sn2
B. Sn1
C. E1
D. E2

I put E2 because there is both the Zaitsev and Hoffman product being formed. But the correct answer is E1. (I thought E1 only yields Zaitsev and not Hoffman). Am I missing something?

 

[Isoprop]

#33: Basically, is an immine group considered an amine functionality?

(the question has a compound with 6 amine groups and 6 immines and it asks for the number of amine functionalities present)

--------------------

#465: Dehydration of 2-hexanol to form 2-hexene and 1-hexene proceeds by what mechanism?

A. Sn2
B. Sn1
C. E1
D. E2

I put E2 because there is both the Zaitsev and Hoffman product being formed. But the correct answer is E1. (I thought E1 only yields Zaitsev and not Hoffman). Am I missing something?

I don't have the book, but I don't really understand the first question. Imines and amines have similar properties but they undergo some pretty different reactions. Sometimes, you can think of imines as oxidized amines.

For the second question, it depends on the base you are using. Both Zaitsev and Hoffman products are formed in both E1 and E2, but Zaitsev is preferred unless we are using a bulky base like tert-butoxide. If we are using a weak base, we will get competition between E1 and E2 (and worse, perhaps even with SN2/SN1). The best way to force E1 is to use concentrated acid. The acid will protonate the alcohol making it a good leaving group and undergo E1. The Zaitsef product will be favored, but we will also get a small amount of the Hoffman product as well.

IMO, it's a bad question. However, E1 is the best answer because dehydration of alcohols are usually done with concentrated acids. I don't expect a question like this to appear on the actual MCAT.

 

[babystepsCA]

#33: Basically, is an immine group considered an amine functionality?
Ans: No. amine has an sp3 N, while imine has an sp2 N. they have quite different chemical properties as well.

#465: Dehydration of 2-hexanol to form 2-hexene and 1-hexene proceeds by what mechanism?
Ans: E1.
First of all this is elimination reaction, hence E.
Second, the reaction forms two product, indicating it goes through a carbocation intermediate, therefore E1.
This should be the answer for MCAT level. In reality, this reaction can be more likely through combined E1 and E2 mechanisms, and also depend on the condition you were actually using.

Let me know if you have further questions.

 

[Rabolisk]

Second, the reaction forms two product, indicating it goes through a carbocation intermediate, therefore E1.

This is not true. E2 reactions also result in 2 products, like E1 reactions. The best answer (as given above) is that (secondary) alcohols usually undergo acid-catalyzed dehydration by E1. E2 would require a moderately strong base, and conjugate bases of strong acids are generally too weak. The only way to force E2 on a primary alcohol is to heat it extremely high temperature (>170 C) or to convert the hydroxide to a different leaving group and use a base.

 

[babystepsCA]

Read my full answer, or quote none.

 

[Rabolisk]

I read your full answer, and the rest of your answer doesn't make the part that is wrong correct.