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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: bluebunny2020 on February 23, 2020, 04:11:37 PM

Title: geminal dibromide elimination
Post by: bluebunny2020 on February 23, 2020, 04:11:37 PM

This question is from Klein 10.46, not really sure why the geminal dihalide reacts to an alkyne when the single-elimination trisub-alkene formation seems more stable? Is there something i'm missing ;-;

(https://i.imgur.com/AD6QlQS.png)

Title: Re: geminal dibromide elimination
Post by: hollytara on February 23, 2020, 07:55:57 PM

Well, it's Klein - I'm not a big fan. 

Had they given you the germinal dibromide at the chain end, there would have been no doubt.

But recognize that the Zaitsev rule that predicts the major product also means there is some of the minor product - in this case the monosubstituted alkene.  The exocyclic alkene for the six membered ring is also somewhat disfavorable, so the minor/major split may not be as bad as it looks (monosubstituted vs trisubstituted). 

The only way to get to the suggested product is through the elimination at the end of the chain to the alkyne.