CHAPTER 3: Question 13

 

Simple Answers

Compound A contains a stereoaxis as shown below, so the two stereoisomers are enantiomers of one another. Enantiomers are optically active and have identical NMR spectra. The extra double bond in compound B however, removes the stereoaxis but allows the formation of cis-trans isomers as shown below. Cis-trans isomers are achiral diastereomers, so they are optically inactive and have different NMR spectra. The stereoisomers of MeCH=C=C=C=CHMe will be enantiomers of one another.
 

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