Estimation of magnetic anisotropy in polycyclic aromatics

Dihydro-dibenzophenanthrene derivatives 1a (1b) were synthesised in order to obtain the NMR shielding parameters for naphthalene ring. The 1H NMR assignment of 1a and substituent-induced shifts (SIS) from the corresponding androstanone ethylene ketal (2) are presented. A simple sum of the magnetic shielding of benzene rings can satisfactorily reproduced the observed SIS values due to the naphthalene ring of 1.