✔ 最佳答案
1.
Properly divide into paragraphs to facilitate reading.
2.
It's "hydration of carbonyl compd.", not just hydration -- there're many kinds of hydration!
3.
Misspell: " nucleophile in type of "H-Y".
4.
Quote your reference: Organic Chemistry by McMurray J.
So that people know what to refer to.
5.
Think of the reaction mechanism: your nucleophile Y attacks the partial-positive carbonyl carbon, so Y must bear lone-pair (NO negative charge, 'coz it's in form of H-Y).
What makes the lone pair more "available" and willing to approach the positive reaction site?
If Y is electronegative (O, Cl, Br) or even attached to electronegative groups (-OSO3H), electrons will be held by Y more tightly; in turn less "available" and less willing to approach the positive site.
On the other hand, if Y is not so electronegative (such as S in H2S and thiols), electrons are less-tightly held, thus more available to attack +ve site.
p.s. You may also want to consider effect of steric hindrance of some nucleophile and the carbonyl compd, but that's another story.
2012-08-31 17:15:20 補充：
1. Since you're using H-Y, so I assume that the medium is acidic; otherwise, your H-Y will deprotonate to give Y(-) anion.
2. If at acidic medium, one can expect the carbonyl oxygen is protonated first, which makes the carbonyl carbon more +ve charged (inductive / resonance).
2012-08-31 17:17:26 補充：
If you're using basic medium, then Y in HY or Y(-) anion would first attack carbonyl carbon; you may need follow-up treatment by acids then.
