Is the C-C stretch infrared active???

[pkandmin]

For the two molecules trans- and cis-Cl(H)C=C(H)Cl, how do i determine

whether or not the C-C stretch is infrared active in each case?

[Kaeroll]

From the little information you've given me I'm guessing this a problem of molecular symmetry?

 

Kaeroll

[Tartaglia]

cis is point group C2v and trans is C2h

 

For cis the symmetric stretch A1 is active in the z direction (C2 axis) not in the x or y so as the C=C is in direction x or y it can't be active

 

For trans the symmetric stretch Ag is not active in x,y or z. and the C=C is in the x or y direction

 

Or more obviously, there is no change in dipole in either on a C=C stretch