phenol

think like this:
one of the lone pair exists in p-orbital, capable to delocalize over the benzene ring, thus stabilizing the whole molecule by dispersing the lone pair charges. this's especially important for phenoxide ion.


2010-09-12 23:20:02 補充：
if there's a structure that allows delocalization of electrons by resonance, eg, benzene ring, naphthalene double-ring, you may safely assume that that atom undergoes sp2 hybridization, leaving an electron pair at pz-orbital for delocalization.

2010-09-12 23:20:18 補充：
in other cases when there's no delocalization by resonance, sp3 is probably adopted.