'The electric dipole moments of six possible rotanlers comprising the two diastereomeric forms of 2,5-dimethyl-2,5-dimetlroxy-3,4-diphenyhexarle have been calculated vectorially.Comparison of these values with the experimental determination of polarization in benzene and carbon tetrachloride shows that only two of the rotamers of the dd,ll form and only one of the meso form are present in significant amount. The moment of the dd,ll diastereomer decreases with increasing temperature but that of the nzeso form is almost invariant. I t is probable that all six central linkages in these diastereomers are hindered from free rotation.T h e two diastereo~ners (Ia and Ib) of 2,5-din~ethyl-2,S-dii~lethoxy-3,4-diphe1~yIhexal1e may be obtained by homopolar reduction of 1-chloromercuri-1-phenyl-2-methoxy-2-nlethylpropane (1). One of these diastereo~ners (Ia) was reported (1) a s a non-crystallizable oil, but we have now succeeded, after chromatographic reilloval of impurities, in the isolation of Ia, as a low-nlelting solid.The configuration of Ia has been established (2) by its conversioil in coilceiitrated sulphuric acid to the related diastereonler of 2,2,5,5-tetramethyl-3,il-diphenyltetrahydrofuran, 11. T h e configuration of this cyclic ether was established as dd,ll because it could be prepared from the diol 111, which was obtained from methyl Grignard reagent and dd,ll-di1~~ethyl-2,3-dipherlylsucci1~ate, IV (3).As might be expected in view of the steric convenience in corlversioil of Ia or I11 to 11, the other diastereotneric (meso) 2,5-din1ethyl-2,5-din~ethoxy-3,4-diphenylhexane, Ib, does not for111 a cyclic ether, V, with ease. It does undergo condensatiorls of the FriedelCrafts type so that the n~ethoxyisopropyl group on one of the central ("pivot") carbon atoms reacts with the ortho position of a phenyl group on the other "pivot" aton1 to form 5,5,10,10-tetra11~ethyl-4b,5,9b,10-tetrahydroindei~o[2,1-a]indene, VI.T h e difference in types of reaction and products forrlled from Ia and Ib would suggest a strong steric influence. Moreover, the specific reactivity with respect to condensing agents (1, 2) shows that the geometry of the diastereomers must be important. For
