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How to determine which compound has the largest overall dipole?

MBAB32D95-4085-4635-9D50-F941194D3180.jpg.jpeg
I know that the answer is nor A or D since they are symmetrical(?) - is it a correct reason?
but how do you determine if the answer is B and not C?
Original post by Xxz39
MBAB32D95-4085-4635-9D50-F941194D3180.jpg.jpeg
I know that the answer is nor A or D since they are symmetrical(?) - is it a correct reason?
but how do you determine if the answer is B and not C?


It's a good reason, as individual dipoles can be resolved and cancelled out.

Overall polarity is caused by individual dipoles not cancelling out. Remember that a dipole has both magnitude and direction.

There is nothing to oppose the dipole created by the carbonyl group in B, but there is the vector of two C-Cl groups that will creat an opposing vector to the carbonyl in C.
Also, the methyl groups in B are electron donating, so there will be more charge on the double bond that can be withdrawn by the carbonyl.
Original post by lordaxil
Also, the methyl groups in B are electron donating, so there will be more charge on the double bond that can be withdrawn by the carbonyl.

I'm not going to disagree with this, as it is a statement oft used in text books (the positive inductive effect), but in reality nothing can "push" electrons, it is more of a case of relatively electropositive atoms (the hydrogens (2.2) bonded to the carbon (2.6) ) allowing their electrons to be attracted to more electronegative atoms.
Original post by charco
I'm not going to disagree with this, as it is a statement oft used in text books (the positive inductive effect), but in reality nothing can "push" electrons, it is more of a case of relatively electropositive atoms (the hydrogens (2.2) bonded to the carbon (2.6) ) allowing their electrons to be attracted to more electronegative atoms.

Yes, complete agree (which is one of the reasons I gave up organic chemistry). In the end, the only thing that is real is the distribution of electron density, which can be calculated directly from the Schrödinger equation for such small molecules, but I guess these heuristic rules allow a shortcut to solution in simple cases.

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