[jumper1127]

Why toluene is a non-polar molecule? It doesn't have a dipole moment?

[macman104]

Yea

[jumper1127]

Yea

I think toluene should have a dipole moment, maybe it's quite weak. The structure is not symmetric.

[nj_bartel]

I would agree that toluene has a very small dipole moment, but you're not seeing the full reason I don't think.  A molecule can be asymmetrical and no net dipole moment.  Precursory glance would suggest toluene has no dipole moment due to all carbon carbon bonds, but the higher electronegativity of sp² orbitals relative to sp³ orbitals may inductively draw some of the electron density out of the methyl group and into the arene, creating a small (pretty much insignificant) dipole moment.

If my reasoning here is wrong, someone please correct me!

[jumper1127]

I would agree that toluene has a very small dipole moment, but you're not seeing the full reason I don't think.  A molecule can be asymmetrical and no net dipole moment.  Precursory glance would suggest toluene has no dipole moment due to all carbon carbon bonds, but the higher electronegativity of sp² orbitals relative to sp³ orbitals may inductively draw some of the electron density out of the methyl group and into the arene, creating a small (pretty much insignificant) dipole moment.

If my reasoning here is wrong, someone please correct me!

It seems that my professor never talked about this in lectures. And my book doesn't talk about this in the dipole moment part either. But we have to deal with this kind of problems in our homework.

[Borek]

0.36 D

[nj_bartel]

I would agree that toluene has a very small dipole moment, but you're not seeing the full reason I don't think.  A molecule can be asymmetrical and no net dipole moment.  Precursory glance would suggest toluene has no dipole moment due to all carbon carbon bonds, but the higher electronegativity of sp² orbitals relative to sp³ orbitals may inductively draw some of the electron density out of the methyl group and into the arene, creating a small (pretty much insignificant) dipole moment.

If my reasoning here is wrong, someone please correct me!

It seems that my professor never talked about this in lectures. And my book doesn't talk about this in the dipole moment part either. But we have to deal with this kind of problems in our homework.

I'd say based on your knowledge, your professor would expect you to consider it nonpolar with no dipole moment, but you should probably ask him.

[macman104]

That is what I was saying nj.  It seemed that you can effecitvely call it nonpolar.  It really has a fairly negligible dipole moment.