2
$\begingroup$

Quick question, in this reaction:

2-Butenal + CH3MgBr --> ??

Will the grignard attack the double-bond or the aldehyde carbon? Please explain this preference, thanks!

$\endgroup$
2
$\begingroup$

The Grignard will first attack the aldehyde carbon, giving you a secondary alcohol. Since the alcohol is strongly polarized, it would be difficult for the double bond to be attacked.

$\endgroup$
4
  • $\begingroup$ Thanks! So just to clarify, the major product will be the secondary alcohol and that is what prevents a second addition. $\endgroup$ – qwersjc Mar 28 '14 at 5:45
  • 1
    $\begingroup$ This does however not explain why Grignard reagents react different than Gilman cuprates ;) $\endgroup$ – Klaus-Dieter Warzecha Mar 28 '14 at 10:26
  • 1
    $\begingroup$ Actually, under the reaction conditions, the magnesium is an ion for the oxygen. This creates a strong negative characteristic to the molecule so the Grignard reagent cannot do a second attack. However, if the alcohol is purified and then reacted with more Grignard reagent, then addition at the double bond is likely. (I'm not familiar with Gilman cuprates.) $\endgroup$ – LDC3 Mar 28 '14 at 13:26
  • $\begingroup$ @ Klaus, I do remember my professor saying something about how Gilman reagants were "soft nucleophiles" and would preserve the carbonyl group. I don't think he explained why this happened though; it would definitely make for another good question. $\endgroup$ – qwersjc Mar 28 '14 at 17:33

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.