Violation of Zaitsev's rules

[thechairman]

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I read somewhere that in the E2 reaction, if the base is too bulky, then Zaitsev's rule may be violated to give the less substituted alkene? can anyone elaborate on this?

 

[Tan008]

i don't remember exactly, but doesn't it have to do with the fact that a bulky base will have trouble removing the internal Hydrogen atom due to the base's streic effects (which is necessary for the creation of the more stable product). Therefore, it will remove a Hydrogen that is more easily accessible creating a Hofmann product.

 

[thechairman]

thanks!

another quick orgo question,

is a double bond more basic (higher pka) than an alcohol. say a question asked if there was a compound with a double bond and an OH group in acid solution, which one would be more likely to be protonated first?

 

[Tan008]

isn't -OH group generally more reactive than a double bond? I'm not too sure here

 

[rhizotummy]

whenever you're thinking about acidity, think about what the conjugate base would look like.

If an alkene is deprotonated, you get a negative charge on a carbon - a fairly non-electronegative atom.

However, if you deprotonate an alcohol, the extra lone pair is on an oxygen - one of the more electronegative atoms.

Hopefully, you can get an answer from here. The point of all this is, instead of memorizing, always draw/visualise the conjugate base to determine relative acidities.

Keep in mind the following things when determining stability:
resonance
electronegativity
inductive effects

good luck👍

 

[axp107]

Sorry to hijack thread.. but does having electron withdrawing groups increase the boiling point of a compound?

 

[scgamer2000]

Does an electron-withdrawing group increase boiling point?

I believe it probably would, but you should probably consider it on a case-by-case basis. If the EWG is going to make the molecule polar, then you'll probably see an increase in boiling point due to increased dipole-dipole interactions.