A Computational Study

In this section, the results of a computational study 48 will be used to illustrate the effects of the solvent—and the significant complexity of these effects—in quantum charge transfer processes. The particular example... 

Helms and McCammon 1997] Helms, V., McCammon, J.A. Kinase Conformations A computational study of the effect of ligand binding. Prot. Sci. 6 (1997) 2336-2343... 

S. H. Oh, Thermal Response of a Monolith Catalyst Converter During Sustained Misfiring A Computational Study, SAE 881591, Society of Automotive Engineers, Warrendale, Pa., 1988. 

Seckler, M.M., Brinsma, O.S.L. and van Rosmalen, G.M. 1995. Influence of hydrodynamics on precipitation a computational study. Chemical Engineering Communications, 135, 113-131. 

The deprotonation of 132 is favored at Ni and the coordination of 135 occurs preferentially at 82- A second entity of 135 coordinates at N3. A computational study of thiouracil derivatives of the tungsten(O) hexacarbonyl shows that the sulfur-bound thiouracil is serving as a ir-donor during the CO dissociation (Scheme 91) [99IC4715]. DFT calculations show that 137 is significantly stabilized with respect to the alternative reaction product 138. 

Note that all the ions involved have already been produced by previous reactions and that apart from those of Reactions 30 and 33 the heats of reaction are small. Thus, with these reactions and similar ones, there is no reason why equilibria should not be maintained. Again, the need to treat a large number of reactions simultaneously to explain the results is stressed. A computer study of such a reaction scheme is now under way at AeroChem. 

The study of the peak temperature sensitivity to the reactor operating parameters and the construction of sensitivity boundary curves for stable reactor operation were previously reported ( l). This paper presents a computer study on conceptual relationships between the conversion-product properties and the reactor operating parameters in a plug flow tubular reactor of free radical polymerization. In particular, a contour map of conversion-molecular weight relationships in a reactor of fixed size is presented and the sensitivity of its relationship to the choice of initiator system, solvent system and heat transfer system are discussed. 

S.G. Davis, J. Quinard, and G. Searby. Markstein numbers in counterflow, methane- and propane-air flames A computational study. Combustion and Flame, 130 123-136, 2002. 

For a computational study on the origin of the enantioselectivity in this reaction, see Dudding T, Houk KN (2004) Proc Natl Acad Sci USA 101 5770-5775... 

Sharma, P., Singh, H Sharma, S. and Singh, H. (2007) Binding of Gold Nanoclusters with Size-Expanded DNA Bases A Computational Study of Structural and Electronic Properties. Journal of Chemical Theory and Computation, 3, 2301-2311. 

The detailed mechanism of this enantioselective transformation remains under investigation.178 It is known that the acidic carboxylic group is crucial, and the cyclization is believed to occur via the enamine derived from the catalyst and the exocyclic ketone. A computational study suggested that the proton transfer occurs through a TS very similar to that described for the proline-catalyzed aldol reaction (see page 132).179... 

The reaction shows a dependence on the E- or Z-stereochemistry of the enolate. Z-enolates favor anti adducts and E-enolates favor syn adducts. These tendencies can be understood in terms of an eight-membered chelated TS.299 The enone in this TS is in an s-cis conformation. The stereochemistry is influenced by the s-cis/s-trans equilibria. Bulky R4 groups favor the s-cis con former and enhance the stereoselectivity of the reaction. A computational study on the reaction also suggested an eight-membered TS.300... 

A computational study of remote directing effects was undertaken in substituted norbornenes.29 It was concluded that polar effects of EWGs favors mercuration at the... 

Jeong, H. Y., Han, Y., Comment on A Computational Study of the Structures of Van der Waals and Hydrogen Bonded Complexes of Ethene and Ethyne Chem. Phys. Lett., 263, 345. 

In many cases the most interesting results of a computational study are the relative energies of transition states and intermediates because they determine the reaction mechanism. In this section we will try to outline when improved active-site geometries can be expected to have important effects on relative energies. 

Santoro F, Barone V, Gustavsson T, Improta R (2006) Solvent effect on the singlet excited-state lifetimes of nucleic acid bases a computational study of 5-fluorouracil and uracil in acetonitrile and water. J Am Chem Soc 128 16312-16322... 

Fabian WMF, Schuppler S, Wolfbeis OS (1996) Effects of annulation on absorption and fluorescence characteristics of fluorescein derivatives a computational study. J Chem Soc Perkin Trans 2(5) 853-856... 

DSMA Atcon, Ltd., A Computer Study of Soil Gas Movement into Buildings, Report 1389/1333, Department of Health and Welfare, Ottawa, Canada (1985). 

A computational study was concerned with the effect of solvation on the radical ion involved in CDP photolyase enzyme-catalysed reversion of thymine and uracil cyclobutane dimers stimulated by visible light <06T6490>. 

Cationic ruthenium complexes of the type [Cp Ru(MeCN)3]PF6 have been shown to provide unique selectivities for inter- and intramolecular reactions that are difficult to reconcile with previously proposed mechanistic routes.29-31 These observations led to a computational study and a new mechanistic proposal based on concerted oxidative addition and alkyne insertion to a stable ruthenacyclopropene intermediate.32 This proposal seems to best explain the unique selectivities. A similar mechanism in the context of C-H activation has recently been proposed from a computational study of a related ruthenium(ll) catalyst.33... 

The selectivity of the hydrogen transfer is excellent When employing a catalyst with deuterium at the a-positions of the isopropoxide ligands (17), complete retention of the deuterium was observed. A computational study using the density functional theory comparing the six-membered transition state (as in Scheme 20.3, the direct transfer mechanism) with the hydride mechanism (Scheme 20.3, the hydride mechanism) supported the experimental results obtained [36]. A similar mechanism has been proposed for the MPV alkynylations [37] and cyanations [38]. 

The focus of the next four chapters (Chapters 14-17) is mainly on the theoretical/computational aspects. Chapter 14 by T. S. Sorensen and E. C. F. Yang examines the involvement of p-hydrido cation intermediates in the context of the industrially important heptane to toluene dehydrocyclization process. Chapter 15 by P. M. Esteves et al. is devoted to theoretical studies of carbonium ions. Chapter 16 by G. L. Borosky and K. K. Laali presents a computational study on aza-PAH carbocations as models for the oxidized metabolites of Aza-PAHs. Chapter 17 by S. C. Ammal and H. Yamataka examines the borderline Beckmann rearrangement-fragmentation mechanism and explores the influence of carbocation stability on the reaction mechanism. 

We performed a computational study [69] to assess which interaction (H bonding, metal-alcoholate formation, or metal-alcohol coordination between the allylic hydoxyl moiety and the Re complex) affects the TS and to determine which oxygen of the Re peroxo moiety acts as H-bond acceptor in the case of an H-bonded TS. A summary of the results with propenol as model allylic alchohol is presented in the following. 

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