I am currently studying nucleophilicity of molecules and am getting a set of conflicting information, so I wanted to clarify nucleophilicity trends with respect to solvent.
Master Organic Chemistry discusses how nucleophilicity increases down the periodic table with protic solvents and decreases down the periodic table with aprotic solvents; the main argument is that a solvating shell will form with the protic solvent, making the smaller atoms less likely to form a bond. When this effect is removed, the trend is reversed.
However, during my lectures, my professor said that there is no such change in the trend: the larger atoms such as $\ce{I-}$ will always be more nucleophilic than $\ce{F-}$ due to the fact that it is more polarizable and likely to donate an electron pair. The textbook that I am using, Organic Chemistry by Wade, also does not discuss this trend reversal depending on the solvent. The only discussion talks about how $\ce{F-}$ would be a poor nucleophile as it is small and holds its electrons "tightly."
A practice problem provided during class also asked to compare the nucleophilic strength between $\ce{H2O}$ and $\ce{H2S}$ in polar aprotic solvent; similarly, the correct answer provided was that $\ce{H2S}$ would be a stronger nucleophile as it is larger and more polarizable.
I would appreciate it if someone could clarify this matter.
No comments:
Post a Comment