Retroene reactions calculations

Semiempirical AMI calculations on the transition state for the retroene-type elimination of propene from allylamines reveal that the most favoured geometry resembles a half-chair or a flattened boat.66 In keeping with experimental observations, it is predicted that electron-donor substituents on nitrogen should promote the reaction since the negative charge on this atom decreases in the polar transition state. 

Table 1.4 lists calculation data on activation and thermodynamic parameters as well as kinetic isotopic effects for three reactions of the retroene type. In the first stage, a search for the transition state structure was conducted and its compatibility with the demands of the Murrell-Laidler theorem verified. Afterwards the vibration frequencies of the reactants and the transition state structure were calculated whose values were used in the corresponding equations. Underestimation of the kinetic isotopic effect in the last two reactions is related to underestimation of the role of the tunnel mechanism (see Sect. 1.5). An exact reproduction of the values of kinetic isotopic effects is a more reliable check on the accuracy of the calculated transition state structures than that of the values of activation entropies. This is explained by the fact that the calculated values of normal vibration frequencies, corresponding to the negative force constants, are directly included into Eqs. (1.24)-(1.26) that determine the magnitude of the kinetic isotopic effect. 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

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