Organic Chemistry Question

[E. coli]

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I am kind of confused on the stability of benzyl and allylic carbocation.

On one of the DAT achiever questions, it says a primary benzyl carbocation is more stable than tertiary carbocation.

However, on my Organic Chemistry Textbook (Prentice Hall by Paula, Yurkanis, and Bruice), it says tertiary carbocation is more stable than primary benzyl carbocation.

(tertiary carbocation > benzyl cation = allyl cation = secondary carbocation > primary carbocation > vinyl cation = methyl cation).

So is the primary benzyl cation more stable than the tertiary carbocation or is it the other way around? How about for secondary or tertiary benzyl carbocation and allylic carbocation? Are they more stable than tertiary carbocation?

 

[mutual]

This problem, together with several other controversial/mistaken ones, have been rectified in Ver. 2 lately, where a tertiary benzyl carbocation is now used to make the final answer 100% right.

However, what you are concerned with here still holds true for the free radicals.

I think it's pretty hard to answer your last few questions without knowing the conditions of each reaction -- something you don't have to worry about as far as the DAT goes.

As a side note here, the advantage of having benzylic carbocation over allylic (both serving as intermediates):

You'll get a single final product in very high yield due the very fact that the phenyl ring has to generally stay intact with its aromacity.

Hope the above input helps to a certain extent. 🙂