CHEM 102 Lecture Notes - Lecture 10: Leaving Group, Propyl Group, Sodium Ethoxide
Document Summary
The stereospecificity of the reactions you have just met is very good evidence that e2 reactions proceed through an anti-periplanar transition state. We know with which diastereoisomer we started, and we know which alkene we get, so there is no question over the course of the reaction. More evidence comes from the reactions of substituted cyclohexanes. that substituents on cyclohexanes can be parallel with one another only if they are both axial. C x bond is anti-periplanar only to c c bonds and cannot take part in an elimination. These two diastereoisomeric cyclohexyl chlorides derived from menthol react very differently under the same conditions with sodium ethoxide as base. Both eliminate hcl but diastereoisomer a reacts rapidly to give a mixture of products, while diastereoisomer b (which differs only in the configuration of the carbon atom bearing chlorine) gives a single alkene product but very much more slowly.
