Conformational analysis of some 1R,4S‐2‐arylidene‐p‐menthan‐3‐ones by ¹H NMR spectroscopy and molecular simulation

Abstract

Based on1 H NMR spectral analysis combined with molecular simulation, conformational states of the cyclohexanone ring were studied for some 1R,4S-2-(4-X-benzylidene)-p-menthan-3-ones (X = COOCH 3 or C 6 H 5 ) in CDCl 3 and C 6 D 6 . The co-existence of chair conformers with an axial orientation of both alkyl substituents and twist-boat forms was established for the compounds studied at room temperature (22-23• C). The substituent X does not influence appreciably the ratio of these conformers, but the fraction of twist-boat forms increases noticeably in benzene solutions as compared with CDCl 3 solutions. Rotameric states of the isopropyl fragment were also characterised for the compounds studied. Distinctions in conformational states for the 1R,4S-2-arylidene-p-menthan-3-ones and (−)-menthone were revealed and are discussed.

Probing NMR parameters, structure and dynamics of 5-nitroimidazole derivatives. Density functional study of prototypical radiosensitizers

“…The theoretical methodologies used to describe solvent effects on spectroscopic properties of molecules can be classified into several groups: continuum models, 31,49 discrete cluster models 50 and molecular dynamics, usually with classical propagation of the nuclei. 51,52 Each has its advantages and drawbacks, and careful validation is necessary in order to identify a particular method (or a combination thereof) that affords reliable results.…”

Molecular structures of regioisomeric 7‐arylidene hexahydroindazoles from 1H NMR spectra

“…They are defined by a repulsive effect between the ortho-hydrogen atoms of the benzene ring and the cyclohexane H6eq atom (Ho· · ·H6eq, Table 5) on one hand and by the conjugation effect in the >N-N C-C C-enhydrazone link on the other. This situation is quite similar to α,β-unsaturated ketones of (+)-isomenthone 2-arylidene derivatives [7] or 3R-methylcyclohexanone-2,6-bis-arylidene derivatives of type 1. [8] A rivalry of the main intramolecular effects exists for all of these compounds.…”

“…A similar preference of axial substituent conformations in the cyclohexane ring was found to be typical for derivatives containing arylidene fragments in α-position to a substituent. [3,7,8,10] Origins of such conformational characteristics, which were considered earlier for arylidene derivatives of chiral cyclohexanones and cyclohexanones, seem to be valid also for cyclohexane compounds with enhydrazone fragment as well. A competition between two main intramolecular effects in molecules of such a type, i.e.…”

“…[2 -6] The study of spatial structure peculiarities of these chiral compounds performed by 1 H NMR and X-ray diffraction methods (see, for example refs. [3,[7][8][9]) allowed to reveal important structural factors determining their rather strong helical twisting power (HTP) in LC systems. In particular, a conformation of the cyclohexanone ring with an axial methyl substituent proved to be significant in many cases.…”

Theoretical and experimental 13C and 15N NMR investigation of guanylhydrazones in solution

“…Data on the calculation of the spectroscopic properties of flexible molecules in solution are scarce 32,33 and the theoretical methodologies described in the literature do not give good results when compared with experimental data. There are other details that are important when using only the solvation continuum model for shielding tensor calculations.…”