Why is sulfide a better nucleophile than the structurally equivalent alkoxide?

1 Answer
Jun 4, 2018

Well, which is the LARGER anion...?


Certainly, third period sulfide anion is LARGER than second period oxide anion....and on this basis its electron cloud is more diffuse, and more polarizable, and thus more likely to participate in a substitution reaction. And CLEARLY, sulfide is a WEAKER base than hydroxide....and clearly the #pK_a# values of water and #H_2S# reflect this.

Taken together, these factors contribute to the superiority of sulfide as a nucleophile...and the superiority of hydroxide as a base.