If you want to ESTIMATE the polarity on basis of single bond dipoles or even on basis of electronegativities it would help if you studied chemistry for ~10 to ~15 years, later concentrating on quantum mechanics. I don´t think this would help too much, though, in predicting the conformation and thus polarity of a molecule which is adsorbed on the stat. phase.
On more practical terms: The C-I bond is also quite polar, yet an iodinated (on the phenol) methyltyrosine has a much higher rt on a C-18 than the methyltyrosine. The C-I dipole seems to counteract another dipole, also, the iodine might figure in the absorption on the stat. phase. I was even more surprised to see that a second I on the ring increases the rt even more, extensively. If I rememeber correctly a similar situation holds with baclofen (a chloro-phenylbutyric acid) in comparison to a derivative with two chlorines on the ring. I don´t think that anybody predicted that either.
