Question

From the IR spectrum organic chemistry lab: Explain why the C=C stretch for a trans-disubstituted alkene is weaker than for a cis-disubstituted akene.

Answer 1

Answer - The C=C stretch for a trans-disubstituted alkene is weaker than for a cis-disubstituted alkene due to the trans alkene is more symmetrical than cis isomer and the C=C in the trans isomer is already stretched due to the symmetrical, so it need less energy for stretching and in the cis there is less symmetrical and the group on the same side make the C=C is contracted, so it need high energy, so C=C stretch for a trans-disubstituted alkene is weaker than for a cis-disubstituted alkene