Question

which of the following will absorb at Higher wavelength.
give reason for your answer
$ch3 - ch = ch - ch3 \\ \\ or \\ \\ ch2 = ch - ch = ch2$

Answer 1

1st is correct....
bcoz as you said higher wavelength means lower energy, and the more stable compound will have lower energy.
in 2nd case all electron clouds remain in the same plane and hence more electronic repulsion occur so stability decreases here.
1st one is more stable and hence lower energy and hence absorb at higher wavelength