Hofmann elimination vs Zaitsev rule

[RCT PC CRN]

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My text book says Hofmann elimination (least substituted) occurs only when there is bulky leaving group like (+N(CH3)) or else follow Zaitsev rule even with bulky base like (-OC(CH3)3)...I believe this contradict Destroyer where it says follow Least sub when bulky base.

Can someone please clarify this for me. (i.e. orgohack 😀)

 

[RCT PC CRN]

I did bit of research online. Many sources say small strong base - Zaitsev and strong bulky base - Hofmann. I think I'm going with this 👍

 

[orgohacks]

I did bit of research online. Many sources say small strong base - Zaitsev and strong bulky base - Hofmann. I think I'm going with this 👍

Yep. If you see tert-butoxide, consider Hoffmann.

 

[Pennpaki]

But isnt that only when you have a tertiary carbocation and bulky base( like chad said)??

 

[orgohacks]

But isnt that only when you have a tertiary carbocation and bulky base( like chad said)??

I can't vouch for what you'll see on the DAT, but in Org 1 exams I've seen multiple examples where t-butoxide as base will give you the Hoffmann product because of steric hindrance. I'm just saying, keep an eye out for it.

 

[Pennpaki]

k cool. Thanks🙂

 

[chromosome21]

My text book says Hofmann elimination (least substituted) occurs only when there is bulky leaving group like (+N(CH3)) or else follow Zaitsev rule even with bulky base like (-OC(CH3)3)...I believe this contradict Destroyer where it says follow Least sub when bulky base.

Can someone please clarify this for me. (i.e. orgohack 😀)

wait.. you said "bulky leaving group"??? I've always thought the bulky base = hofmann elimination. But didn't know hofmann elimination can also occur with a bulky leaving group. It does seem like it may occur. But can anyone provide an example of it? Thanks

 

[RCT PC CRN]

wait.. you said "bulky leaving group"??? I've always thought the bulky base = hofmann elimination. But didn't know hofmann elimination can also occur with a bulky leaving group. It does seem like it may occur. But can anyone provide an example of it? Thanks

+N(CH3)3 is a bulky LG and it's classic Hofmann Elimination.

 

[orgohacks]

wait.. you said "bulky leaving group"??? I've always thought the bulky base = hofmann elimination. But didn't know hofmann elimination can also occur with a bulky leaving group. It does seem like it may occur. But can anyone provide an example of it? Thanks

Scroll down to #6 on this page:

http://is.gd/dgp0z

Main principle is that it is E2 like, but you are minimizing steric interactions, so less substituted alkene is favored.