Conformational Analysis in Mobile Cyclohexane Systems

Abstract

By "Conformational Analysis" is meant the analysis of the physical and chemical propertiesof a compound in terins of its preferred"conformations", i. e. rotational arrangements about single bonds. This particular review deals with cyclohexanoid compounds capable of existing in two or more stable conformations.

First Principles of Prediction of Thermodynamic Properties

“…Cyclodecane has considerably more conformational flexibility (Hendrickson, 1964;Eliel et al, 1965;Almenningen, Bastiansen & Jensen, 1966;Rounds & Strauss, 1978;Dobler, Dunitz & Mugnoli, 1966;Burgi & Dunitz, 1968;Egmond & Romers, 1969;Srinivasan & Srikrishnan, 1971;Anet & Basus, 1973;Anet, 1974;Meiboom, Hewitt & Luz, 1977;Pakes, Rounds & Strauss, 1981;Burkert, 1982;Brecknell, Raber & Ferguson, 1985;Saunders, 1987;Lipton & Still, 1988;Chang, Guida & Still, 1989;Dorofeeva et al, 1990;Ferguson et al, 1992;Kolossvary & Guida, 1993;Weinberg & Wolfe, 1994;Wiberg, 2003) than the smaller C7-C9 cycloalkanes discussed in the previous Sections. The structures of the lower-energy conformations have been studied via electron diffraction (Hilderbrandt, Wieser & Montgomery, 1973), X-ray crystallography (Shenhav & Schaeffer, 1981) and dynamic NMR spectroscopy (Pawar et al, 1998).…”

“…Nevertheless, even for a pure substance, the structure and measured properties reflect the behavior of many distinct geometries (conformers) averaged by the Boltzmann distribution. In general, for flexible molecules, several conformers can be found and the analysis of the physical and chemical properties of these isomers is known as conformational analysis (Eliel, 1965). In most of the cases, the conformational processes are associated with small rotational barriers around single bonds, and this fact often leads to mixtures, in which many conformations may exist in equilibrium (Franklin & Feltkamp, 1965).…”

Organic chemistry section:

“…The substitution of an oxygen atom for a methylene group introduces the influence of the unshared pairs of electrons, which, apart from such consequences as van der Waals interactions [18] and London attractive forces [19], may result in the development of hydrogen bonding [20].…”

Isolation by crystallization of translational isomers of a bistable donor-acceptor [2]catenane

“…Translational isomerism does not fall under this umbrella: hence, our introduction (17, 18) of the term co-conformation to describe a particular kind of translational isomerism that is observable using dynamic NMR spectroscopy (22). Just as dynamic NMR spectroscopy was employed (23,24) in the 1960s to probe the equilibration of conformational diastereoisomers; e.g., the axial and equatorial isomers of chlorocyclohexane (25) and to study the conformational behavior of mediumsized ring compounds (26) (27) incorporating a tetrathiafulvalene (TTF) unit and a 1,5-dioxynaphthalene (DNP) one was employed subsequently to good effect in molecular switch tunnel junctions (MSTJs) in two-dimensional molecular electronic devices (2D MEDs) with crossbar architectures (31, 32). On account of the much stronger binding (33) of TTF to cyclobis(paraquat-p-phenylene) (CBPQT 4þ ) compared with DNP, the bistable [2]catenane ( Fig.…”

“…Translational isomerism does not fall under this umbrella: hence, our introduction (17,18) of the term co-conformation to describe a particular kind of translational isomerism that is observable using dynamic NMR spectroscopy (22). Just as dynamic NMR spectroscopy was employed (23,24) in the 1960s to probe the equilibration of conformational diastereoisomers; e.g., the axial and equatorial isomers of chlorocyclohexane (25) and to study the conformational behavior of mediumsized ring compounds (26) in the 1980s, it has become possible, during the past decade, to investigate co-conformational equilibria in bistable donor-acceptor [2]catenanes (27) and [2]rotaxanes (28)(29)(30). The first really robust and efficient switchable [2]catenane (27) incorporating a tetrathiafulvalene (TTF) unit and a 1,5-dioxynaphthalene (DNP) one was employed subsequently to good effect in molecular switch tunnel junctions (MSTJs) in two-dimensional molecular electronic devices (2D MEDs) with crossbar architectures (31,32).…”