Hi Melissoy, good question! It looks good on paper, but the short answer is no. The long answer is the nature of teaching a subject as vast and exception-riddled as organic chemistry is that an individual professor might teach some interesting exception. If your teacher has said it can happen, follow that. Otherwise, no, generally speaking PBr3 is limited to primary and secondary alcohols undergoing an SN2-style reaction. I'm not aware of any textbook that teaches PBr3 can do an SN1-style reaction with a tertiary alcohol. If anyone else has I would be thrilled if they could point me to it. Hope that helps!
