How many stereoisomers does 2,5-dibromohex-3-ene, CH3-CHBr-CH=CH-CHBr-CH3, have? Count enantiomers, diastereomers and E/Z isomers as distinct, and give the answer as an integer.

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JEE Advanced levelNumerical answerDifficulty 3 of 3st196

How many stereoisomers does 2,5-dibromohex-3-ene, $CH X_{3} - CHBr - CH = CH - CHBr - CH X_{3}$ , have? Count enantiomers, diastereomers and E/Z isomers as distinct, and give the answer as an integer.

Numerical answer type, tolerance 0.5.

Answer: 6

The molecule is symmetric (C2

\leftrightarrow

C5). For each double-bond geometry (E or Z) the two stereocentres can be (R,R), (S,S) or (R,S); (R,S) and (S,R) are the same meso compound because of the symmetry. That gives 3 for E and 3 for Z. Total = 6, compared with the naive

2^{3} = 8

(checked by explicit enumeration).

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How many stereoisomers does 2,5-dibromohex-3-ene, CHX3​−CHBr−CH=CH−CHBr−CHX3​, have? Count enantiomers, diastereomers and E/Z isomers as distinct, and give the answer as an integer.

Answer: 6

More questions on Diastereomers, meso compounds and counting stereoisomers

How many stereoisomers does 2,5-dibromohex-3-ene, $CH X_{3} - CHBr - CH = CH - CHBr - CH X_{3}$ , have? Count enantiomers, diastereomers and E/Z isomers as distinct, and give the answer as an integer.