[simonsci]

Hi everyone! I was asked to distinguish cis-but-2-ene and trans-but-2-ene by infrared spectroscopy. I know the trans isomer shows an absorption band at 1680 to 1600 cm^-1, as it has a C=C bond and is asymmetrical. The cis isomer doesn't have this feature since it is symmetrical.

But the solution manual says the trans isomer is symmetrical and the cis isomer is asymmetrical. Why?

[simonsci]

I get it!