The Energy Barrier for the Chair-Chair Interconversion of Cyclohexane

Jensen, Frederick R.; Noyce, Donald S.; Sederholm, C. H.; Berlin, Alvin J.

doi:10.1021/ja01490a061

Cited by 95 publications

(26 citation statements)

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“…With increasing temperatures the lines corresponding to the two sites broaden and finally merge into a single sharp resonance. The process associated with the change in line shape is in all likelihood the chain-chain interconversion in which axial and equatorial protons exchange roles (45). Similar processes have been observed in dithiane (46) and per fluorocyclohexane (47).…”

Section: Rates and Mechanisms By Nuclear Magnetic Resonancesupporting

confidence: 59%

Nuclear and Electron Spin Resonance

Weissman¹

1961

Annu. Rev. Phys. Chem.

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This review is restricted to the chemical application of nuclear and electronic magnetic resonance. Cross relaxation, Maser action, most of the work on dynamic polarization, and use of the Mossbaurer effect for observing magnetic resonance will not be classified 'as chemical. The discussion will be divided into sections on the magnetic resonance of electronically diamagnetic and paramagnetic materials respectively. The former contains nuclear reso nance (NMR) almost exclusively, while the latter includes both nuclear and electronic resonance (ESR). HIGH RESOLUTION SPECTROSCOPY OF DIAMAGNETIC MOLECULESAs the available instruments improve and the factors governing attain able resolution come under better control, the quality of spectra appearing in the literature improves correspondingly. The depth of interpretation of high resolution spectra has ranged from empirical assignment of chemical shifts and spin-spin coupling constants, to attempts to calculate all the details of the spectrum of a molecule from sufficiently accurate wave functions.The positions and intensities of all the lines in NMR spectra are most conveniently summarized by numerical parameters in phenomenological or spin Hamiltonians. The parameters are, in addition to the magnetic mo ments of the nuclei, chemical shift constants for each of the nuclei and spin spin coupling constants for each pair of nuclei. With appropriate isotopic substitutions it is usually possible to obtain the constants in the spin Hamil tonian from the spectra, but the process is laborious for complicated mole cules.Corio (1) has given a carefully worked out review of methods for deter mining the parameters in the spin Hamiltonian from the spectrum. He makes full use of symmetry and conservation properties. While the methods may seem too abstract to many who work in NMR, they are essential for an economical solution of the problems that arise.As examples of complete determination of the parameters in spin Hamil tonians, we may cite work on ethyl acetylene (2, 3) and ethyl mercaptan (2), ethyl derivatives of mercury, silicon, zinc, and germanium (4, 5) substituted ethylenes (6), propenes (7, 8), butenes (9), and vinyl compounds (10).The spectrum of propane has been analyzed by an elegant theoretical method (11) that takes full advantage of the molecular symmetry, and by 1 The survey of literature pertaining to this review was concluded on December 15, 1960. 2 The following abbreviations will be used: NMR, nuclear magnetic resonance; ESR, electron spin r�sonanr.�. 151 Annu. Rev. Phys. Chem. 1961.12:151-170. Downloaded from www.annualreviews.org Access provided by Michigan State University Library on 02/03/15. For personal use only. Quick links to online content Further ANNUAL REVIEWS

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Section: Rates and Mechanisms By Nuclear Magnetic Resonancesupporting

confidence: 59%

Nuclear and Electron Spin Resonance

Weissman¹

1961

Annu. Rev. Phys. Chem.

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“…Nevertheless, in p-dioxane, the free-energy barrier to chair inversion is lower than in cyclohexane, since distinct p.m.r. signals for axial and for equatorial protons are observed for cyclohexane [16] below -66.7°C, but not for p-dioxane [17] even at -104°C.…”

Section: It Wasmentioning

confidence: 82%

Organic chemistry section:

Schaffer¹

1969

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“…36 Moreover, temperaturedependent NMR spectra are only devoted to the determination of the kinetic parameters for the chair ↔ chair interconversion. [37][38][39][40] There are two kinds of the diagonal C ·C distances in a cyclohexane molecule. The shorter C·C distance appears at 255 pm commonly for the chair and boat conformers.…”

Section: Liquid Cyclohexanementioning

confidence: 99%

Analysis of Liquid Structure without Construction of Any Structure Models by the X-Ray Scattering Method

2007

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Since a study on liquid paraffin by Debye and Scherrer, 1 a large number of structural studies on various liquids have been conducted by the X-ray scattering method. The structure of liquid water in various conditions has been examined by many investigators.2,3 Structural information on organic liquids has also been accumulated. [4][5][6][7] Due to large fluctuations caused by molecular motions in long distant regions, analyses of a liquid structure by the X-ray scattering method require one to make up a local structure model, i.e., an aggregate consisting of several liquid molecules, which best reproduces the X-ray scattering data.The simplest approach to deduce a structure model of a liquid will refer to a partial structure present in its crystal when the crystal structure has been determined. The interstitial model of liquid water by Narten 8 is the most famous example. Determinations of the local structure of organic liquids such as benzene, formamide, dimethyl sulfoxide, and N-methylacetamide at ambient temperature (their melting points are 5. 493, 2.55, 18.55, and 30.55˚C, respectively) are successful examples based on the partial structure in the crystal. [9][10][11][12] In order to obtain further information on the longer range intermolecular interactions of molecular liquids, Iijima and Nishikawa proposed the reciprocal space expansion in the analysis of X-ray scattering data. 13,14 However, these procedures do not apply if the temperature of a liquid is far from its melting point because of large differences of densities between solids and liquids. The intermolecular distances among molecules in a liquid are quite different from those in a solid phase.Another approach to construct a liquid structure is one that uses physicochemical properties of liquid molecules. When a liquid is protic and has a hydrogen-bonding ability, a two-or three-dimensional hydrogen-bonded network should be taken into account. For an aprotic polar liquid molecule, a negatively charged atom of a molecule approaches a positively charged atom of another molecule according to the charge distributions of the molecules. Also, molecules are piled up interacting with their dipole moments in an antiparallel way. Considering these patterns, one searches for molecular arrangements which reproduce X-ray scattering data well by a trial-and-error method. A good example is the structural determination of liquid acetonitrile. [15][16][17][18][19] However, analysis by this approach is a laborious task. Thus, a simple approach for determining a liquid structure without constructing any plausible structure models is necessary.Two methods have been used frequently for studying liquid structures without constructing any plausible models, i.e., the reverse Monte Carlo (RMC) 20 method and the empirical potential structure refinement (EPSR) 21 method. The RMC method is the computer simulation based on the Metropolis Monte Carlo procedure: a particle or a molecule moves so as to decrease the difference between the experimental scattering data and cal...

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The Energy Barrier for the Chair-Chair Interconversion of Cyclohexane

Cited by 95 publications

References 0 publications

Nuclear and Electron Spin Resonance

Nuclear and Electron Spin Resonance

Organic chemistry section:

Analysis of Liquid Structure without Construction of Any Structure Models by the X-Ray Scattering Method

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