‘Monte Carlo’ computer simulation of chain molecules III. Simulation of<i>n</i>-alkane molecules

Lal, Madan; Spencer, D.

doi:10.1080/00268977100102911

Cited by 43 publications

(10 citation statements)

References 14 publications

(14 reference statements)

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“…The distance of 0.87 nm between C6DI2 neighbors in the fcc lattice serves as an estimate for the effective size of the cage that is left for the guests. With Monte Carlo statistics for the description of the conformational motion of the polymethylene chain [2,22], for the 1,7-biradical formed during the photolysis of cycloheptanone we calculate that the average distance between the radical ends is about 0.7 nm. One can assume that the biradical is rather flexible and moves fast in its cage when substituting one C6Dl2.…”

Section: Results and Diseussionmentioning

confidence: 99%

Field dependence of CIDNP in photoreactions in plastic crystalline matrix

2004

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Photo-CIDNP (chemically induced dynamic nuclear polarization) of three ketones (cycloheptanone, cyclodecanone, and acetone) in cyclohexane-d~2 and its dependence on the external magnetic field (0-7 T) is measured in liquid, plastic crystalline and rigid crystalline phases by temperature variation between 185 and 300 K. Spin polarization is seen only in liquid and plastic crystalline phases, but not in the rigid crystal giving evidence that molecular mobility is a requisite for the formation of CIDNP. From the characteristics of the field dependence the mechanisms of polarization are identified and properties of paramagnetic reaction intermediates determined. The factors causing the observed differences in polarization between the liquid and the solid phase are discussed in detail.

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Section: Results and Diseussionmentioning

confidence: 99%

Field dependence of CIDNP in photoreactions in plastic crystalline matrix

2004

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“…For the description of the conformational motion of the polymethylene chain of the biradical, an end-to-end distance distribution function C ( r ) was calculated . We used a calculation based on the Monte Carlo computer program for simulation of n -alkanes developed by Lal and Spenser . The conformation energy U k is composed of the bond rotational energies and the energy due to the interaction among nonbonded atoms in the molecule.…”

Section: Resultsmentioning

confidence: 99%

Spin and Molecular Dynamics of Biradicals as Studied by Low Field Nuclear Polarization at Variable Temperature

et al. 1999

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1H and 13C chemically induced dynamic nuclear polarization (CIDNP) and time-resolved stimulated nuclear polarization (SNP) have been applied to the investigation of spin and molecular dynamics in biradicals, generated in the photolysis of 2,2,12,12-tetramethylcyclododecanone, at low magnetic field in the temperature range from 200 to 360 K. This reaction involves two consecutive biradical stages, the primary acyl−alkyl and the secondary bis-alkyl biradical, with different reaction products. Characteristic differences in the CIDNP field dependencies and SNP decay times for nuclei of different reaction products are seen at high temperatures. Upon cooling, the emission maximum position shifts to low field and the width of the 1H CIDNP field dependencies of the acyl−alkyl biradical products decreases. Below 243 K these effects reverse direction, furthermore, a significant slowing down of the SNP decay is observed. Calculations of the 1H and 13C CIDNP field dependencies and the SNP kinetics for the primary biradical have been performed based on the numerical solution of the stochastic Liouville equation for the biradical spin density matrix. They use a model of restricted diffusion for the description of the molecular dynamics and take into account the distance dependence of the exchange interaction. Good quantitative agreement between the calculations and experimental data is found for the whole temperature range when using the appropriate dependence of some of the parameters on temperature. In particular, it was necessary for the quantitative simulation in the low temperature range to introduce a temperature dependence of the biradical reactivity. The model calculations qualitatively confirm that the low-temperature broadening of the CIDNP field dependencies, and the increase of the SNP decay time are caused by the slowing down of the molecular mobility and the decreasing of reactivity. For the products of the secondary biradical, a qualitative interpretation is given showing that in comparison with the products of the primary biradical spin−orbit interaction is of less importance for the biradical spin dynamics, that the influence of the molecular mobility under the temperature variation is more pronounced, that the lifetime is longer, and that the nuclear polarization is more efficiently formed.

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“…The quality of the results of molecular mechanics calculations depend on the chemical accuracy of the force field parameters. The most favorable conformers are found by minimizing the energy of structures or by a search of the conformational space either systematically or randomly. − …”

Section: Introductionmentioning

confidence: 99%

“…The conditions of the simulation can be allowed to vary during a trajectory, and studies can be made at higher temperatures and pressures than are possible experimentally. The static and dynamic properties of a material can also be calculated by Monte Carlo (MC) simulations. , The molecular dynamics methods to be applied to both equilibrium and nonequilibrium situations for the conformational and other properties of molecules. Molecular dynamics has widely been applied to the modeling of liquids. − …”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Study of the Conformational Properties of Branched Alkanes

1997

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Molecular dynamics simulations were carried out to study the conformational properties of branched alkanes (C40H82). The populations of different isomeric conformers, cooperative transitions, and transition rates by analyzing a trajectory at 450 K in the gas phase were calculated. The results extracted from the molecular dynamics trajectory were mostly in very good agreement with the results for previously simulated n-alkanes.

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‘Monte Carlo’ computer simulation of chain molecules III. Simulation ofn-alkane molecules

Cited by 43 publications

References 14 publications

Field dependence of CIDNP in photoreactions in plastic crystalline matrix

Field dependence of CIDNP in photoreactions in plastic crystalline matrix

Spin and Molecular Dynamics of Biradicals as Studied by Low Field Nuclear Polarization at Variable Temperature

Molecular Dynamics Study of the Conformational Properties of Branched Alkanes

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