[Rutherford]

If the dipole moment of 1.3-dichlorobenzene is 5*10^-30, what is the dipole of the ortho-isomer?

I am really stuck here, not sure what to do.

[sjb]

If the dipole moment of 1.3-dichlorobenzene is 5*10^-30, what is the dipole of the ortho-isomer?

I am really stuck here, not sure what to do.

I think you have to assume that the chlorines work independently, and that the hydrogens don't affect things as much

Draw something like a free-body diagram  ( http://en.wikipedia.org/w/index.php?title=Free_body_diagram&oldid=501916435 ) to work out what the dipole moment would be due to a single C-Cl, then re-evaluate given the change in geometry going from 1,3 to 1,2-dichlorobenzene

[Rutherford]

Seems like this requires more geometry. I draw these diagrams, and I wrote the important angles, and using trigonometry (length of the dipole is the longest line) I got the right answer. Thanks.