Cope computational studies

Winter, R. F., Rauhut, G. Computational studies on 3-aza-Cope rearrangements protonation-induced switch of mechanism in the reaction of vinylpropargylamine. Chem.- Eur. J. 2002, 8, 641-649. 

Kontogiannis, T. (1996), Stress and Operator Decision Making in Coping with Emergencies, International Journal of Human-Computer Studies, Vol. 45, pp. 75-104. 

Cope and Sila-Cope Rearrangements Computational studies by Yates et ed. on 1,5-enynes were used to rationalize the different regioselectivities observed for the Au(I)-catalyzed addition of alcohols to the all carbon (X = C) and silyl 1,5-enynes (X = Si) as shown in Eq. (5.9) [35]. 

Quantum chemical studies of cyclizations of enediynes and enyneallenes have been reviewed.180 The intermediates are computationally tractable as a result of the unrestricted broken spin symmetry (UBS) approach using GGA functionals for the description of open-shell biradicals. The intermediacy of biradicals in Cope-type rearrangements, to which the Bergman and Myers-Saito reactions belong, are shown to be predictable using a very simple rule biradicals are likely to be intermediates if they are stabilized either by allyl resonance or by aromaticity. 

A number of theoretical studies have been conducted to understand the mechanism of the Cope rearrangement.16 According to calculations by Houk and co-workers, the chairlike transition state is more stable than the boatlike transition state by 7.8 kcal/mol (Scheme l.XII). When Schleyer and colleagues performed calculations to compute the magnetic properties of the transition-state structures, transition states A and B had a magnetic susceptibility of—55.0 and—56.6, respectively. These values are comparable to that of benezene (—62.9), confirming the existence of an aromatic transition state in the Cope rearrangement. 

We first take up the prototype Bergman cyciization, which is the conversion of (3Z)-3-hexene-l,5-diyne (38) into jo-benzyne (40). Computational chemists came to the Bergman cyciization problem at about the same time as they came to understand the computational difficulties of the Cope rearrangement discussed in the previous section. These studies of the Cope rearrangement greatly colored the early choice of methodologies to be used for the Bergman cyciization. 

Molecular polarizabilities and hyperpolarizabilities are now routinely calculated in many computational packages and reported in publications that are not primarily concerned with these properties. Very often the calculated values are not likely to be of quantitative accuracy when compared with experimental data. One difficulty is that, except in the case of very small molecules, gas phase data is unobtainable and some allowance has to be made for the effect of the molecular environment in a condensed phase. Another is that the accurate determination of the nonlinear response functions requires that electron correlation should be treated accurately and this is not easy to achieve for the molecules that are of greatest interest. Very often the higher-level calculation is confined to zero frequency and the results scaled by using a less complete theory for the frequency dependence. Typically, ab initio studies use coupled-cluster methods for the static values scaled to frequencies where the effects are observable with time-dependent Hartree-Fock theory. Density functional methods require the introduction of specialized functions before they can cope with the hyperpolarizabilities and higher order magnetic effects. 

Even more impressive is the development of appropriate analytics. Modern NMR technology reveals such perfect complementarity as in the case of glycopep-tides at levels of atomic resolution, providing virtual threedimensional models of ligand protein interaction. Bacterial resistance and means to cope with it, can be discussed by studying models of chiral interaction in the computer. 

In conclusion, an illuminating insight of the reaction path is obtained by means of a rather naive, but inexpensive method of computation. Other reactions studied along these lines, include the addition of methylene to ethylene 76>, addition and insertion of sulfur to ethylene 77>, dimerization of methylenes and nitroso compounds 78> fragmentation of cyclo-butane to ethylenes 79>, the Cope rearrangement 80>, the interaction of tricycloalkanes with acids and bases 81>, and the polytopal rearrangements in (CH)s, (CH)i, and (CH CO systems 82). 

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