[CrimpJiggler]

I've read about halide ions being nucleophiles but have never heard of neutral halogens acting as nucleophiles. I'll use CH3F as an example. This is a highly polar molecule, the should have a strong partial negative charge. Why doesn't the flourine atom add to electrophiles such as carbonyl carbons?

[CaverKat]

Are you suggesting this?



- Strong covalent C-F bond (540 kJ mol^-1).  Energy imbalance if breaking one of the C-O bonds.
- Making the highly electronegative (and very happy F) electron deficient.

[JustinCh3m]

In general, are halide ions (in alkyl halides) better:

1. leaving groups?

-OR-

2. nucleophiles?

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answering this may help you with your question...

[CrimpJiggler]

I know halides make good leaving groups. I don't know what the relationship between leaving groups and nucleophiles is though.

[shona788]

It's obvious that halide ions are good nucleophiles, since they have -ve charge and are attracted to +ve charge

The neutral halide CH₃F however,is polar i.e. there is a  :delta:+ on the carbon and a  :delta:- on the fluorine. Since fluorine is a better leaving group than a nucleophile, in the presence of a nucleophile e.g. a base, the carbon prefers to act as an electrophile being attacked by the base, pushing the fluorine out since it is a good leaving group. E.g. an SN2 mechanism