TPR Complete test 3 #44 C/P

[akimhaneul]

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For this question, I understand why B is the answer. But I don't understand why CHCl2F has a weaker dispersion force than CCl2F2. It seems to me that CHCl2F is more polar in general than CCl2F2. Can anyone explain this? Thanks!

 

[aldol16]

It's not immediately obvious and whether CHCl2F or CClF2 is more polar depends on cis/trans configurations, but the latter molecule probably fits together better with other like-molecules. It has four halogens instead of three halogens and one proton so it's more likely to present a more continuous surface for dispersion forces. However, this is not obvious at all and I wouldn't expect something like this on the MCAT.