The The mechanism of reaction between 3-hydroxy-3-methyl-2-butanone and malononitrile for the synthesis of 2-dicyanomethylene-4, 5, 5-trimethyl-2,5-dihydrofuran-3-carbonitrile catalyzed by lithium ethoxide was investigated by density functional theory (DFT). The geometries and the frequencies of reactants, intermediates, transition states and products were calculated at the B3LYP/6-31G(d) level. The vibration analysis and the IRC analysis verified the authenticity of transition states. The reaction processes were confirmed by the changes of charge density at the bond-forming critical point. The results indicated that lithium ethoxide is an effective catalyst in the synthesis of 2-dicyanomethylene-4, 5, 5-trimethyl-2, 5-dihydrofuran-3-carbonitrile from malononi-trile and 3-hydroxy-3-methyl-2-butanone. The activation energy of the reaction with lithium ethoxide was 115.86 kJ·mol−1 less than the uncatalyzed reaction. The mechanism of the lithium ethoxide catalyzed reaction differed from the mechanism of the uncatalyzed reaction.
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The numerical simulation of the internal motions of a molecule undergoing a unimolecular reaction on an assumed potential energy surface requires the step-by-step solution of a set of simultaneous differential equations. After several thousand time steps, due to differences in the handling of rounding errors in different computing systems, the situation often arises that no two computing machines will give the same result for a given trajectory, even when running the identical algorithm. Such effects are demonstrated for a simple unimolecular isomerisation reaction. In general, it is only when reliance is placed on the integration of a single trajectory, rather than on an ensemble of similar trajectories, that conclusions may be unreliable. Moreover, under certain conditions, small molecules may show signs of chaotic internal motions; conversely, but for a different reason, large molecules may exhibit non-statistical characteristics rather than RRKM behaviour. The rounding error problem, in a slightly different guise, has come to be dubbed the “butterfly effect” in popular culture, and the original proposition is re-examined using 16- and 32-decimal precision arithmetic. [...]
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