Question

The presence of 11-cis retinal, C20H28O, in cells in the eye is important for vision.
The structure of retinal includes an aldehyde group, a cyclohexene ring and a long aliphatic side
chain, in which a carbon-carbon double bond exists between carbons numbered 11 and 12.
Which pair of statements about 11-cis retinal could be correct?

5 C=C bonds and R1/R2 around the C=C bond between carbons 11 and 12 being on the same side
5 C=C bonds and R1/R2 around the C=C bond between carbons 11 and 12 being on opposite sides side
6 C=C bonds and R1/R2 around the C=C bond between carbons 11 and 12 being on the same side
6 C=C bonds and R1/R2 around the C=C bond between carbons 11 and 12 being on opposite side

I automatically knew that the R1/R2 hydrocarbon groups had to be on the same side because it's a cis compound, which eliminates two of the answers, but then how do you figure out the number of C=C double bonds with only that information and the molecular formula?

Answer 1

5 C=C bonds and R1/R2 around the C=C bond between carbons 11 and 12 being on the same side