Experimental and theoretical investigation of the inversion of configuration during thermal nitrogen loss from 2,3-diazabicyclo[2.2.1]hept-2-ene-exo,exo-5,6-d2

Lyons, Barbara; Pfeifer, Joerg; Carpenter, Barry K.

doi:10.1021/ja00023a093

Cited by 13 publications

(14 citation statements)

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“…This picture is supported by the previous trajectory calculations. 4 The pictorial representation of the reaction dynamics can be translated into a semiquantitative prediction of the product ratio.6 The Cartesian atomic displacements corresponding to the reaction coordinate represent the elements of a 3iV-dimensional vector (where N is the number of atoms). We hypothesize that the product ratio can be estimated by comparing components of the mass-weighted reaction coordinate vector along directions leading to post-transition-state minima on the potential energy hypersurface (in the case of 2 these minima would correspond to the two products, 4x and 4n, and to cyclopentane-1,3-diyl-m-4,5-t72…”

mentioning

confidence: 99%

Estimation of dynamic effects on product ratios by vectorial decomposition of a reaction coordinate. Application to thermal nitrogen loss from bicyclic azo compounds

Peterson¹,

Carpenter²

1992

J. Am. Chem. Soc.

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confidence: 99%

Estimation of dynamic effects on product ratios by vectorial decomposition of a reaction coordinate. Application to thermal nitrogen loss from bicyclic azo compounds

Peterson¹,

Carpenter²

1992

J. Am. Chem. Soc.

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“…Cho et al . , and Vande Linde and Hase have found the reaction between Cl - and CH 3 Cl to involve nonstatistical behavior with extensive barrier recrossings and intramolecular dynamics that are not in accord with transition-state assumptions. Carpenter and co-workers − have found striking nonstatistical branching ratios in several systems whose reaction mechanisms involve large, biradical species.…”

Section: Introductionmentioning

confidence: 99%

Statistical and Nonstatistical Dynamics in the Unimolecular Decomposition of Vinyl Bromide

Kay

Raff

1997

J. Phys. Chem. A

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Rate constants have been computed for three unimolecular decomposition reactions of vinyl bromide for several energies in the range 5.23−7.67 eV, using statistical variational efficient microcanonical sampling−transition-state theory (EMS-TST) on a global vinyl bromide potential energy surface. The EMS-TST results are compared with those obtained from a previously reported classical trajectory study on the same potential energy surface [J. Phys. Chem. 1995, 99, 2959] in order to assess the extent to which vinyl bromide unimolecular decomposition is governed by statistical dynamics. For the three-center HBr elimination reaction, it is found that k EMS-TST is greater than k trajectory by a factor of 1.5−3.5 over the energy range considered. For the C−Br bond scission, the EMS-TST and trajectory results at lower energies are equal within the statistical error in the trajectory calculations, while at higher energies k EMS-TST exceeds k trajectory by a factor of 1.4−2.9. The EMS-TST calculations also reproduce a surprising result from the trajectory study, that the rate constant for three-center HBr elimination is an order of magnitude greater than that for C−Br bond scission throughout the energy range, even though the barrier height for the latter reaction is 0.34 eV lower. These results imply that three-center HBr elimination and C−Br bond scission are governed by statistical dynamics. For the three-center H2 elimination reaction, however, k trajectory is greater than k EMS-TST by a factor of 2−4 at lower energies and a factor of 5−7 at higher energies. This result necessarily implies that the dynamics of the three-center H2 elimination are nonstatistical. The nonstatistical behavior for this reaction is attributed to a breakdown in the coupling among vibrational modes as the H2 fragment departs, which leaves energy in excess of the statistically predicted amount in the dissociation coordinate. A study of intramolecular vibrational relaxation (IVR) rates and pathways in vinyl bromide [J. Phys. Chem. 1996, 100, 8085] supports this conclusion. The IVR analysis also shows that such a breakdown in mode-to-mode coupling does not exist for the three-center HBr elimination and that nearly global randomization of the internal energy rapidly occurs as the system moves through the transition-state region for HBr elimination. Thus, the nature of IVR on the vinyl bromide potential surface used in this work is consistent with the present EMS-TST results showing that three-center HBr elimination is well-described by statistical reaction rate theory, while three-center H2 elimination is not.

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“…When such energetic changes occur, there will frequently be an enhanced coupling between the dissociation coordinate and the remainder of the molecule that leads to increased IVR rates and decreased reaction rates, both of which will tend to eliminate nonstatistical effects. A second principle postulated by Carpenter and co-workers [28][29][30][31][32] is that nonstatistical behavior will become more prevalent as the energy of the reacting system approaches threshold. Our results [33][34][35][36][37][38] tend to support this hypothesis.…”

Section: Introductionmentioning

confidence: 99%

“…We have recently begun to examine the dynamics in reactions involving the formation of biradicals which Carpenter's recent work [28][29][30][31][32] suggests will often exhibit nonstatistical branching ratios. Using a projection method of the instantaneous Cartesian velocities onto the normal mode vectors 2,3,38 and classical trajectory methods, the dissociation dynamics of 2,3-diazabicyclo ͑2.2.1͒hept-2-ene-exo, exo-5,6-d 2 have been investigated at several excitation energies in the range 60-175 kcal/mol.…”

Section: Introductionmentioning

confidence: 99%

Intramolecular energy transfer rates for vinyl bromide and deuterium-substituted vinyl bromides from power spectrum line splittings

Pan

Raff

1997

The Journal of Chemical Physics

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Analysis of the intramolecular charge transfer in donor-acceptor α,α′-substituted oligothiophenes from their vibrational spectra Doorway state enhanced intramolecular vibrational energy redistribution in the asymmetric = CH 2 hydride stretch of methyl vinyl ether Continuous frequency modulated ͑CFM͒ line splittings are used to determine the energy transfer rate coefficients for the local C-Br and CvC vibrational modes in vinyl bromide and the C-H stretching modes in doubly deuterium-substituted vinyl bromides. The global potential developed by Abrash et al. is employed in all calculations. Energy transfer rate coefficients are extracted from the fine structure spacing of the numerically computed power spectrum of the bond coordinates. The consistency of the averaged individual rate coefficients is evaluated by comparison with results obtained from local mode energy decay curves. It is found that the total intramolecular vibrational relaxation ͑IVR͒ rate coefficients for all modes investigated are large relative to the unimolecular decomposition rate. However, previous studies show that IVR is not globally rapid so statistical behavior of the unimolecular reaction is not expected. It is shown that near overlapping resonances in the power spectrum make it difficult to accurately extract CFM line splittings. This limitation effectively precludes the use of power spectra to investigate IVR rates for some modes. For the specific case of vinyl bromide, it is demonstrated that the C-Br and CvC stretching modes have sufficiently isolated bands that IVR rates out of these modes can be determined from the line splittings. However, the superposition of the three C-H stretching fundamentals makes it essentially impossible to investigate these modes in vinyl bromide. For the case of doubly deuterium-substituted vinyl bromides, the C-H stretching fundamental is well isolated so that IVR relaxation rates can be easily obtained from the power spectrum line splittings. The consistency of the IVR rate coefficients obtained from line splittings is investigated by calculation of these coefficients from the envelopes of bond energy decay curves. The differences between the two results varies from 15% for the CvC stretch to 43% for one of the C-H stretching modes. The average deviation is 30% which is in accord with the accuracy of the method ͑Ϯ25%͒ previously estimated by Agrawal et al. The effect of initial local excitation energy on the line splittings and associated rate coefficients is investigated for the C-Br stretching mode. The results show that the line splitting and rate coefficients are nearly independent of excitation energy below 0.8 eV. Above this energy, both the line splittings and the IVR rate coefficients increase rapidly. This is interpreted as being due to increased intermode coupling at higher energies produced by the greater vibrational anharmonicity. It is concluded that CFM line splittings can be effectively used as a probe of energy transfer rates in six-atom molecules provided the modes under examination hav...

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Experimental and theoretical investigation of the inversion of configuration during thermal nitrogen loss from 2,3-diazabicyclo[2.2.1]hept-2-ene-exo,exo-5,6-d2

Cited by 13 publications

References 1 publication

Estimation of dynamic effects on product ratios by vectorial decomposition of a reaction coordinate. Application to thermal nitrogen loss from bicyclic azo compounds

Estimation of dynamic effects on product ratios by vectorial decomposition of a reaction coordinate. Application to thermal nitrogen loss from bicyclic azo compounds

Statistical and Nonstatistical Dynamics in the Unimolecular Decomposition of Vinyl Bromide

Intramolecular energy transfer rates for vinyl bromide and deuterium-substituted vinyl bromides from power spectrum line splittings

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