¹H and ¹³C NMR studies of the conformational mobility of 1,2-dimethoxybenzene in solution

Abstract

. Can. J. Chem. 68, 1393 (1990). IH NMR and 13C NMR spectral data are presented for 1,2-dimetho~~benzene-a,a'-~~C, as well as for a number of other anisole derivatives. For the title molecule, the coupling constants between the I3C nucleus in the side chain and the para ring proton or 13C nucleus in the benzene ring show that the expectation value of sin2 8 is very near 0.2 at 300 K, where 8 is the angle by which the methoxy groups twist out of the aromatic plane. This value of (sin2 8) is much larger than that of 0.05 for anisole in solution, emphasizing the greater conformational mobility of the methoxy groups in 1,2-dimethoxybenzene (DMB). Long-range coupling constants between the methyl and ring protons in DMB are also discussed and compared with those in anisole and some of its derivatives. The preponderance of conformations with large values of 8, thought to occur in the vapor, disappears in solution at ambient temperatures. Under these conditions, the molecule is perhaps best described as preferring a planar conformation in which, however, the methoxy groups undergo excursions in 8 whose average value is near 25".Key words: 1,2-dimethoxybenzene, conformational behaviour, internal mobility, long-range coupling constants, I H and I3C NMR. Introduction The conformational behaviour of 1,2-dimethoxybenzene (DMB), veratrole, has been studied extensively with somewhat mixed results. Early STO-3G MO computations, with geometries based on calculations for anisole, have the 0°,900 (see 1)

Identification of 2,4-diamino-6,7-dimethoxyquinoline derivatives as G9a inhibitors

“…18 Since the benzenoid ring is important for inhibitory activity, the role of the dimethoxy substituents on this ring should be questioned. Desmethoxyquinazoline derivatives (34-37) were found to be far less active against G9a, which is in agreement with a recent report on related analogues, [35][36][37][38][39][40][41][42] and demonstrates that these substituents are also of importance. A number of theoretical and experimental studies have shown that orthodimethoxybenzenes prefer to adopt a co-planar conformation, with the sp 2 oxygen lone pairs projecting towards each other and the corresponding methyl groups angled away from each other.…”

Exploring the Aqueous Vertical Ionization of Organic Molecules by Molecular Simulation and Liquid Microjet Photoelectron Spectroscopy

“…Previous studies have explored the conformations of the structural analogue ODMB in different organic solvents. Authors have reported the solvent dependence of planarity versus nonplanarity of ODMB in low-temperature glasses and in the liquid phase. − However, the experimental reports leave it unclear whether nonplanarity implies only a temporary departure from planarity within the basin centered at the planar minimum, or whether, like in the gas phase, stable nonplanar conformers exist. To the best of our knowledge, there are no published data for the conformer populations of ODMB in the aqueous phase.…”

From anisole to 1,2,4,5‐tetramethoxybenzene: Theoretical study of the factors that determine the conformation of methoxy groups on a benzene ring

“….n(O) interactions between the two methoxy groups. However, from the data available in the literature the coplanar arrangement seems to be the most stable, which would mean that ultimately mesomeric stabilization determines the observed conformations [27][28][29][30][31][32]. In contrast, it is conceivable that this mesomeric stabilization will change when methoxy groups are moved to other positions on the benzene ring or when more methoxy groups or other mesomerically active groups are introduced.…”