Which one is a dipole and why? Isomers

Question

These are three isomers of dibromobenzene as follows in the list down below

So Which molecule or molecules are

dipoles and why? How does their structural formula play a role in this? Justification/ motivation required.

a) 1,2-dibromobenzene

b) 1,3-dibromobenzene

c) 1,4-dibromobenzene

would really appreciate a detailed answer thank you.

Answer 1

I cannot easily draw any of them on this platform, but hopefully you can. When you do, you'll see that 1,4-dibromobenzene has the Br atoms opposite one another on the benzene ring. Br is a very electronegative atom and so draws electrons toward it. In the 1,2, and 1,3 isomers, this results in a dipole being formed. But in the 1,4 isomer, the pull in opposite directions basically cancel each others effect, and it is not a dipole. Hope that explains things satisfactorily.