EFFECTS ON THE N.M.R. SPECTRA OF THE STEREOCHEMISTRY OF 3,4-DIARYLADIPIC ESTERS AND 1,2-DIARYLCYCLOPENTANES

Abstract

Examination of the n.m.r. spectra of cis- and trans-1,2-diphenylcyclopentane and 3,4-diphenylcyclopentanone substituted in the para positions of both rings with methoxyl, methyl, and chloro substituents has shown that the previous explanation (1) of the effect of temperature on the n.m.r. spectra of 1,2-diphenylcyclopentane and 3,4-diphenylcyclopentanone (unsubstituted) was incorrect. The n.m.r. spectra provide no evidence of restriction of rotation of the aromatic rings of these compounds. An alternative explanation is offered.Comparison of the spectra of the compounds above and those of meso- and dl-3,4-diphenyl-adipic esters with the para substituents mentioned leads to the observation that in the dl-adipates and the cis-cyclopentanes the position of absorption of the protons ortho to the central structure (HR) is shifted to higher field compared to the corresponding meso or trans isomer by an amount ranging from 0.2 to 0.7 p.p.m. The protons ortho to the substituent X (HX) are also shifted to higher field but by only about 0.1 p.p.m.Shifts of the benzylic protons of the trans-cyclopentanes and cyclopentanones to higher field amount to 0.3–0.6 p.p.m. in agreement with previous work (1, 34). The corresponding shift of the benzylic protons of the meso-adipic esters is only 0.1–0.2 p.p.m. The methylene protons and the methyl ester protons of the meso-adipates are also shifted to higher field by about 0.3 and 0.2 p.p.m. respectively.These shifts seem adequately explained in terms of ring current effects of the benzene rings and lead to the possibility of obtaining detailed information concerning the stereochemistry of such substances. They are of immediate value in making configurational assignments to related compounds.