Hoffman vs Zaitsev

[i4everpaki]

Hoffman is the minor product
Zaitsev is the major product

How can you tell which product forms. i just can't seem to understand. if some one can explain this with an explanation it will be helpful.

Thank you

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[katarin]

I think if the alkene is reacting with an unhindered base like MeO- then the major, Zaitsev product forms being the more stable structure. If you have a reaction with a strong but huge, bulky base like (CH3)3CO-, then it will most likely yield a Hoffman product with a less substituted double bond because the base will have a hard time reaching and attacking the most substituted carbon atom.

Here's a Wiki page for more info or I recommend referring back to your textbook 🙂
http://en.wikipedia.org/wiki/Zaitsev's_rule

 

[i4everpaki]

ok so its a simply E2 reaction with strong or weak base. any other reaction that follow this principle?

 

[journeybegins]

ok so its a simply E2 reaction with strong or weak base. any other reaction that follow this principle?

If I'm not mistaken, E2 reactions typically happen under strong bases. If it's a weak base, it would favor E1.

Either way, E1 or E2, you would still get a double bond.


Anyone can correct me, since I'm not stellar at ochem but my understanding of this is that..


Different kinds of bases would you give you different products

a unhindered, strong base like NaOCH3 --> yields the Zaitsev, which is the more substituted alkene

a bulky, hindered, strong base like (CH3)3COK --> yields Hoffman, which is a less substituted alkene


They differ in terms of mechanism, which H you are removing to form the double bond.

Check out the following powerpoint that I just googled. Look at slide 22 and 23 (for Zaitsev) vs. 53 and 54 (for Hoffman), the beta hydrogen that you remove is different so you get different alkene products.

http://www.google.com/url?sa=t&sour...lazOAw&usg=AFQjCNEF8_ybSpGbViWHJ4Xct9bUjk5j3Q

Hope that clears up some things 🙂

 

[journeybegins]

Another thing:

strong bases favor E2.
weak bases favor E1.

🙂

 

[i4everpaki]

ok cool, thank you guys. i understood it. E2 elimination with a bulky base gives hoffman product and E2 elimination with "simple" base gives zaitsev. and correct it has to be a strong base with E2. E1 will not be able to give zaitsev.

 

[orgohacks]

ok cool, thank you guys. i understood it. E2 elimination with a bulky base gives hoffman product and E2 elimination with "simple" base gives zaitsev. and correct it has to be a strong base with E2. E1 will not be able to give zaitsev.

E1 will always give you the Zaitsev.
I think you meant E1 will not be able to give Hoffmann? 🙂

 

[i4everpaki]

E1 will always give you the Zaitsev.
I think you meant E1 will not be able to give Hoffmann? 🙂

ya thanks for clearing it up.