The direction of the dipole moments of phosphabenzene and arsabenzene

THE DIRECTION OF THE DIPOLE MOMENTS OF PHOSPRABENZENE AND ARSABENZENE Arthur J. Ashe, III *1 and Woon-Tunq Chan Department of Chemistrv, Universitv of Michigan Ann Arbor, Wichiqan 48104 (Bcceived in USA 2 June 1975; received rn UK for publication 26 June 1975) Preliminary studies of the spectral properties of phosphabensene (phosphorin) ,? and arsabenzene (arsenin) 2 have emphasized their similarities to 2-6 pyridine . Recently we reported the gas phase dipole moment of phosphabenzene as 1.54D5 and that of arsabenzene as l.10D6. The magnitude is considerably less than that for pyridine ,& (2.215D)7. The direction of the dipole was not determined. Since the difference in electronegativity8 between nitrogen (3.04) and carbon (2.55) relative to phosphorus (2.19) and carbon (2.55) and to arsenic (2.18) and carbon (2.55) changes sign, one might naively expect a change in the dipole moment direction as well. On the other hand both CNDO/2g'10 and ab initio 11 -MO calculations have predicted that all three heterobenzenes have the same direction of polarization. It was felt desirable to test this prediction. A compariscn of the dipole moments of 4-substituted heterobenzenes with those of the parents should unambiguously define the direction of the moments. We now wish to report on the synthesis of 4-methylphosphabenzene 2 and 4-methylarsabenzene