Question

ORGANIC CHEMISTRY: E1 AND E2 REACTION LAB

Discuss the outcome of E1 reaction products: 1-butene, trans-2-butene and cis-2-butene.

Results: Percent composition of products in order: 3.29%, 34.7%, 62.02%

1. cis-2-butene was formed as my major product, why? Explain in detail.

2. 1-butene and trans-2-butene formed as my minor product, why? Explain in detail.

(I know trans-2-butene should have been my major product, but something must have gone wrong through out the lab)

Answer 1

In general in E1 elimination process higher alkyl substituted product will form as a major product.

The reaction thermally controlled reaction. If we supply sudden heat minor product will be formed as major product.  

In general trans alkene is more stable than Cis product due to the arrangement of methyl groups is far away from each other, so that less repulsions possible between the methyl groups. So the systematic supply of heat energy favours the predominant product (trans). Whereas the Cis will be dominated in some cases by supply of unexpected heat energy. Also both Cis and trans isomers interconvertable on supply of heat energy.

Conclusion: this reaction is thermodynamically controlled so that unexpected products were dominated.