¹H‐NMR study of some new acetyl dimethylbiphenyls: unambiguous signal assignment for the methyl groups

Abstract

The abundance1H-NMR spectra of some new mono- and diacetyl compounds derived from 2,2′-dimethyl-, 3,3′-dimethyl-, and 4,4′-dimethylbiphenyls were recorded. Unambiguous signal assignment of the methyl groups of the aromatic biphenyl rings were made for the structure elucidation.

A reactivity-selectivity study of the Friedel-Crafts acetylation of 3,3′-dimethylbiphenyl and the oxidation of the acetyl derivatives

“…Acetylation in 1,2-dichloroethane with acetic anhydride and aluminium chloride was reported [36] to give the 4-acetyl derivative (50%) and the same product was obtained (38.5%) when the reaction was carried out in carbon disulphide [37]. Diacetylation of 3,3′-dmbp has been mentioned only briefly in the literature [30]. Other electrophilic substitution reactions of 3,3′-dmbp include chlorination that gives a mixture of 2-, 4- and 6-chloro-3,3′-dmbp with the 4-isomer being dominating [38], bromination and iodination that lead to the 4-halo derivatives [39] and sulphonation [40] that with an excess of 98% H 2 SO 4 leads to a 52:48 mixture of the 4,4′-and 4,6′-disulphonic acids.…”

“…The 1 H NMR spectral data of the acetyl derivatives illustrate that the chemical shift of the methyl protons could be used as an indication of the position of substitution of an acetyl or a methyl group linked to the aromatic rings [ 30 , 41 , 42 ]. Analysis of the 1 H NMR data showed that the methyl protons chemical shifts (δCH 3 ) for all the three isomers are shifted downfield by 0.15 ppm compared to the methyl protons in the parent compound.…”