[MJF]

We are learning about NMR and we just went through shielding and deshielding. But this question has me puzzled a little bit. Here are the two choices:

a) CH3CH3 (just imagine an arrow pointing to the 2nd carbon)

b) CH3CH2Cl (arrow pointing to the Carbon of the CH2)

Our professor stated that for Choice B, the CH2 is an electron withdrawing group and the signal is going to move to the left, because the shielding moves to the left.

But he also lectured that there is lower frequency when the signal moves to the right. With an EWG attached to an atom, the signal moves left but there will be a higher frequency. So what exactly is going on here?

Bonus Question- Is an electron withdrawing group an atom that is more electronegative than the atom it is attached to?

MJF

[discodermolide]

Just a point here, the CH₂ is not an electron withdrawing group, the Cl is.

In general an electron withdrawing group is more electronegative than the atom it is attached to.

[Altered State]

First of all, "groups" don't give NMR signals, nucleus do.
I guess, since you are starting, you talk about 1H NMR, so those arrows shouldn't point to carbons, but to hydrogens.. (In case you are learning 13C NMR, it would be kinda the same reasoning)

That being said, the more DESHIELDED (electron density substracted by any other atom or functional group) a nucleus is, the more chemical shift it will show (i.e, it will show up more "to the left").
If you know that, you just need to tell which compound has a more electron-withdrawing "thing" near the nucleus you are studying (in the first compoud all H are the same and it the second one there are 2 kinds).