[clara226]

If I have an OH group on an alkane and I want it to be a Br, can I do an SN1 by protonating the OH and then having it come off to leave a carbocation, then have the Br add?  Also, can I do the reverse of I have Br attached to an alkane and then add NaOH (except I'm guessing that this would be an SN2?  Or would it matter which is a better nucleophile/which is a better leaving group when I'm trying to do that? 

[UG]

If I have an OH group on an alkane and I want it to be a Br, can I do an SN1 by protonating the OH and then having it come off to leave a carbocation, then have the Br add? 

Depends on the type of alcohol you have, if you have a tertiary alcohol, the carbocation intemediate formed is quite stable and reaction with HCl or HBr will first protonate the alcohol and then loss of H₂O followed by reaction with halide ion will give the alkyl halide. For primary and secondary alcohols however you may want to consider a S_N2 reaction where the OH is first converted into a better leaving group by reaction with SOCl₂ or PBr₃ and subsequent displacement by the halide ion to give the final product.

Also, can I do the reverse of I have Br attached to an alkane and then add NaOH (except I'm guessing that this would be an SN2?  Or would it matter which is a better nucleophile/which is a better leaving group when I'm trying to do that? 

Here things can get quite messy as you have competing elimination and substitution reactions, different substrates and solvents etc... may favour one or the other, it depends.