This was done with the UHF/sto-3g Scan=Opt command in Gaussian94

A simple SN1 reaction: A flourine(yellow) atom approaches a Bromo-methane molecule, pushing off the Br (red) to form Flouro-methane.

Notice when we have bulky methyl groups the flourine atom does not push the Br off. Instead the F atom cleaves a hydrogen forming HF.

(continue...)

Dan Lawson