The lousy nucleophile

Chemistry Level 3

Fluoride ions are very strong bases as they have very high charge density (thus, making them highly reactive) and are also able to make very strong bonds with hydrogen ions (thus, having a rather stable conjugate acid). With such high reactivity and high basic strength, wouldn't the fluoride ion be an exceptionally good nucleophile? However, it may not seem to be the case all the time. Explain why.

Fluorine is a very electronegative element. Thus, fluoride would not want to donate its electrons. Fluoride ions are heavily solvated in polar protic solvents, greatly reducing its nucleophilicity. The valence atomic obitals are too low in energy to donate its electron pair. Being electronegative, it is able to stabilise its negative charge and become much less reactive.

Tan Yong Boon by Tan Yong Boon , 20, Singapore

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1 solution

Suhas Sheikh
May 29, 2018

Nucleophilicity is directly related to base strength and the availability of lone-pairs of the nucleophile The high degree of solvation causes fluoride ion to lose some of this availability and hence the lesser nucleophilicity in aqueous medium

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