The enthalpy of isomerisation of methyl isocyanide

Baghal-Vayjooee, Mohammad H.; Collister, John L.; Pritchard, H. O.

doi:10.1139/v77-366

Cited by 63 publications

(32 citation statements)

References 5 publications

(1 reference statement)

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“…The percentage of C-X lengthening at the transition state may be defined as the Distortion Index, DI (eq. [12]). This reflects the "tightness" or "looseness" of the transition state.…”

Section: Interpretation Of the Results In Terms Of The Scd Modelmentioning

confidence: 99%

Relationships between geometries and energies of identity S_N2 transition states: the dominant role of the distortion energy and its origin

Mitchell¹,

Schlegel²,

Shaik³

et al. 1985

Can. J. Chem.

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At the 4-31G computational level, the intrinsic barriers of eight identity SN2 reactions X 3-CH3X XCH3 + X-are less than the energies required to distort CH,X from its ground state geometry to its transition state geometry by a constant 25 kcal/mol. The distortion energy and its C-X stretching and H-C-X bending components can be calculated directly, or, alternatively, estimated from the force constants and bond dissociation energies of CH3X. Regardless of the mode of computation, the distortion energies are found to be dominated by the C-X stretching deformations, and these are linearly correlated with the intrinsic barriers. The total deformation energies are also linearly correlated with the intrinsic barriers. The transition vectors of the eight identity reactions have been calculated; each is dominated by the C-X stretch. The percentage of C-X stretching at the transition state, here termed the Distortion Index (Dl), reflects the "tightness" or "looseness" of this structure. The intrinsic barrier increases as the D1 increases, i.e., as the transition state becomes more "exploded". This result does not agree with the predictions of a More O'Ferrall-Jencks potential energy surface diagram. However, as shown in some detail, all of the computational results of the present work are in harmony with the surface crossing diagram model of the barrier. The essential feature of this model is the notion that the activation process in an identity SN2 reaction is a result of the distortion that is required to transfer one electron from X-to CH,X. DAVID JOHN MITCHELL, H. BERNHARD SCHLEGEL, SASON S. SHAIK et SAUL WOLFE. Can. J. Chem. 63, 1642 (1985).Des calculs au niveau 4-3 IG indiquent que les Cnergies des barrieres intrinseques de 8 reactions SN2 d'identite: X-+ CH,X 4 XCH3 + X-sont systematiquement 25 kcal/mol de moins que celles requises pour dCformer le CH3X de sa gtomktrie de

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“…The percentage of C-X lengthening at the transition state may be defined as the Distortion Index, DI (eq. [12]). This reflects the "tightness" or "looseness" of the transition state.…”

Section: Interpretation Of the Results In Terms Of The Scd Modelmentioning

confidence: 99%

Relationships between geometries and energies of identity S_N2 transition states: the dominant role of the distortion energy and its origin

Mitchell¹,

Schlegel²,

Shaik³

et al. 1985

Can. J. Chem.

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“…Schneider and Rabinovitch estimated the degree of self-heating in their highpressure reactions on the basis of a AH of isomerisation of -15 kcal mol-' and a thermal conductivity of 0.25 mW cm-' deg-'. We have recently remeasured both AH as -23.70 + 0.14 kcal mol-' (65) and the thermal conductivity, about 0.20 mW cm-' deg-' at 230°C (66), which implies that all of the correction factors for self-heating estimated by Schneider and Rabinovitch are too small by about a factor of two. It seems likely that if sufficient raw experimental data are still available to enable these self-heating corrections to be calculated properly, some of the present discrepancies might be eliminated.…”

Section: A the Shape Of The Fall-08 Curvementioning

confidence: 95%

A reformulation of the theory of unimolecular reactions

Yau¹,

Pritchard²

1978

Can. J. Chem.

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PRITCHARD. Can. J. Chem. 56, 1389(19783 The theory of unimolecular reactions is reformulated in a way which makes no reference t o the concepts of a transition state, a reaction coordinate, or of an activated complex: the present theory is based, instead, on a simple master-equation approach using the estimated positions and lifetimes of the rotation-vibration energy levels of the molecule. The fundamental basis of this reformulation is that the unimolecular rate is derived from the perturbation of the normal modes of internal relaxation of the reactant molecule by the microscopic reaction processes. The thermal decompositions of cyclobutane, cyclopropane, ethyl isocyanide, ethyl chloride, and methyl isocyanide are examined in detail, and it is shown that not only is the present theory much easier to use than is conventional RRKM theory, but also that it gives better results.An Appendix provides a set of algorithms required for these calculations. Un appendice fournit l'ensemble d'algorithmes requis pour ces calculs.[Traduit par le journal]

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“…Potassium atoms in the 4d states are probably produced by photodissociation of K 2 dimers as the beam PL passes through HP2. Figure 6 shows increasing exposures of upconverted spectra with "300 torr of CH 4 in the 18cm long sample cell. The CH 4 Q-branch is marked.…”

Section: It T K -#Fmentioning

confidence: 99%

“…Upconverted spectra have also been recorded with NH 3 To demonstrate the transient capability of the new technique, the isomerization of methyl isocyanide to methyl cyanide was studied. This well-known isomerization, exothermic -by 23.7kcal/mole [4], has been suggested as an ideal unimolecular reaction for testing thermal explosion theories. [5] Recently we observed…”

Section: It T K -#Fmentioning

confidence: 99%

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The enthalpy of isomerisation of methyl isocyanide

Cited by 63 publications

References 5 publications

Relationships between geometries and energies of identity S_N2 transition states: the dominant role of the distortion energy and its origin

Relationships between geometries and energies of identity S_N2 transition states: the dominant role of the distortion energy and its origin

A reformulation of the theory of unimolecular reactions

Time-resolved infrared spectral photography

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The enthalpy of isomerisation of methyl isocyanide

Cited by 63 publications

References 5 publications

Relationships between geometries and energies of identity SN2 transition states: the dominant role of the distortion energy and its origin

Relationships between geometries and energies of identity SN2 transition states: the dominant role of the distortion energy and its origin

A reformulation of the theory of unimolecular reactions

Time-resolved infrared spectral photography

Contact Info

Product

Resources

About

Relationships between geometries and energies of identity S_N2 transition states: the dominant role of the distortion energy and its origin

Relationships between geometries and energies of identity S_N2 transition states: the dominant role of the distortion energy and its origin