[DoctorDomo]

Lets say I have some insanely activated (for NAS reactions) benzene ring like pentachloronitrobenzene or something, and I react it with an organic nucleophile like t-Butyl alcohol or something. Where happens to the Cl atoms that get displaced? Since the alcohol has to lose a H, would I be right in thinking it'll leave as HF? Or what about a grignard reagent, would it leave as MgFBr?

[Babcock_Hall]

Do you mean pentafluoro, as opposed to pentachloro?

[DoctorDomo]

Sorry, I meant to say HCl, not HF, but lets say pentafluoronitrobenzene instead. What happens to the flourine atoms? Does it get released as F2 gas, HF, a salt, or what? For example, lets say I use sodium ethoxide as my nucleophile, when the nucleophilic ethoxide ion attacks the carbon, the F- ion leaves, so in this case I'm guessing it just pairs up with Na+ to form a salt, but I'm just theorising there, I could be wrong.

[Babcock_Hall]

It would probably leave as fluoride ion and make a salt.  It would have to be oxidized to become fluorine gas.

[critzz]

Yes, you are right. The leaving fluoride-ion ends up with the sodium-ion (from the NaOEt) to form NaF.

[orgopete]

... react it with an organic nucleophile like t-Butyl alcohol or something...

An alcohol isn't nucleophilic enough. It needs to be an alkoxide or an amine.