Of these two molecules, which one would be expected to have the most deshielded signal?
First off, I think the wording of this question is wack because neither of these molecules has only one NMR signal.
In any case it's clear that the question is asking about which molecule has the highest degree of electron withdrawal ...
I chose E, because I was looking at the benzene's signals. This one has an alkyl group, which is a slight inductive donor, thereby shielding the benzene's protons (slightly). This one also has a benzylic carbonyl group, which, according to my teacher, is only a resonance withdrawer and not in any form a resonance donator. Based on this, I chose E as the more de-shielded.
The other group similarly has a C=O resonance withdrawing group, but a resonance donating -OH group. Given that the resonance effect usually trumps the inductive effect, I said that E is still the more deshielded of the two.
I realize I might have now erred in limiting my analysis of shielding to only the hydrogens on the benzene. In E, the methyl's hydrogens are fairly well-shielded still, being connected to a carbon (albeit an sp2 hybridized carbon). On the other hand molecule F has a long linear chain; the hydrogens toward the end of that linear chain will have well-shielded signals! F's linear chain is also longer than E's linear chain ...
Frankly I think this is a horrible question but in any case the answer is apparently "F" ... do you agree?