Consider the compound octa-2,6-diene-4,5-diol, $CH X_{3} - CH = CH - CH (OH) - CH (OH) - CH = CH - CH X_{3}$ . Counting all configurational stereoisomers (E/Z isomers of both C=C bonds and R/S isomers of both $CH (OH)$ centres; enantiomers and diastereomers counted separately, meso forms counted once), how many stereoisomers exist? Give the answer as an integer.

Numerical answer type, tolerance 0.5.

Answer: 10

The molecule is symmetric about the C4-C5 bond, so labelled configurations (C2=C3, C4, C5, C6=C7) that map to each other by swapping the two halves are the same compound. Of the 16 labelled combinations (2 x 2 x 2 x 2), those with identical halves (same E/Z and same R/S at both centres) number 4 and are self-paired. Distinct = (16 + 4)/2 = 10.

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Answer: 10

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