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Nicole_5521
#1 Posted : Sunday, August 01, 2021 7:40:04 AM
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Hi,

For Q18, how come compound 2 is more polar than compound 1? I thought since there was the HOH2C group at the top left, it would balance out the dipoles in the molecule as a whole, since there's also the NH2 - S=O group at the bottom left.

In general, what steps should we follow to distinguish the polarity between large compounds like these ones?

Thanks!
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INSTR_Katrina_128
#2 Posted : Tuesday, August 03, 2021 5:31:26 PM
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That "balancing" effect would work if the molecule was symmetrical, but it's not! That molecule is a mess. 😲 So, because of an additional UNBALANCED change with the addition of that HOH2C group (which has some OH's on it -- these are polar), the polarity is increased.

With large molecules like these, play "spot the difference". The only difference between these two molecules is that HOH2C group. Is this group polar? This one is. It has OH's in it. Then ask yourself, is this molecule "balanced"? (i.e. symmetrical) This one isn't. So, adding a polar group to an unbalanced molecule will make the molecule MORE polar.
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