Computer evidence

A concerted [2 + 2] cycloaddition pathway in which an oxametallocycle intermediate is generated upon reaction of the substrate olefin with the Mn(V)oxo salen complex 8 has also been proposed (Scheme 1.4.5). Indeed, early computational calculations coupled with initial results from radical clock experiments supported the notion.More recently, however, experimental and computational evidence dismissing the oxametallocycle as a viable intermediate have emerged. In addition, epoxidation of highly substituted olefins in the presence of an axial ligand would require a seven-coordinate Mn(salen) intermediate, which, in turn, would incur severe steric interactions. " The presence of an oxametallocycle intermediate would also require an extra bond breaking and bond making step to rationalize the observation of trans-epoxides from dy-olefms (Scheme 1.4.5). 

Given the zwitterionic natnre of single carbenes, the possibility exists for coordinating solvents such as ethers or aromatic compounds to associate weakly with the empty p-orbital of the carbene. Several experimental stndies have revealed dramatic effects of dioxane or aromatic solvents on prodnct distribntions of carbene reactions. Computational evidence has also been reported for carbene-benzene complexes. Indeed, picosecond optical grating calorimetry stndies have indicated that singlet methylene and benzene form a weak complex with a dissociation energy of 8.7kcal/mol. ... 

The relationship between the geometry of the saddle point of index one (SPi-1) and the accessibility to the quantum transition states cannot be proved, but it can be postulated [43,172], To some extent, invariance of the geometry associated with the SPi-1 would entail an invariance of the quantum states responsible for the interconversion. Thus, if a chemical process follows the same mechanism in different solvents, the invariance of the geometry of the SPi-1 to solvent effects would ensure the mechanistic invariance. This idea has been proposed by us based on computational evidence during the study of some enzyme catalyzed reactions [94, 96, 97, 100-102, 173, 174, 181-184],... 

A final example that is so remarkable to deserve mention is the photoisomerization of alkenyne 61 to its isomer 63 (equation 21)149. In a recent reinvestigation of the reaction, Johnson and coworkers have provided computational evidence for the intermediacy of the 1,2-cyclobutadiene isomer 62 in the phototransposition reaction150. 

Mallinson, L. G., J. L. Hutchinson, D. A. Jefferson, and J. M. Thomas (1980). Internal structure of nephrite experimental and computational evidence for the coexistence of multiple chain silicates within an amphibole host. Phil. Trans. Roy. Soc. London 295 537-552. 

To date, no computational evidence has been presented to support these reaction mechanisms. Moreover, monomeric nickel vinylidene complexes have not been characterized outside of matrix isolation [37]. Given the unique properties of disilacyclobutenes, the significance of this work in the context of metal vinyli-dene-mediated catalysis remains to be established. 

In all cases, the calculations identify the singlet species as the more stable one at the PMP-4 level, the singlet states of FpP—C—SiFp and (FpNpP—C—SiFp are 5.6 and 13.9 kcalmol-1, respectively, below the triplet states. Thus, all computational evidence points to a description of (R2N)2P—C—SiR3 as a species with a P,C multiple bond, with an emphasis on the ylide structure II in which both charges are stabilized by the respective neighboring substituents. An X-ray structure determination of one of the isolable [bis(dialkylamino)phosphino](silyl)carbenes is not yet available but, as will be shown in... 

The methodology for obtaining the zr-and (-/-energies for zr-systems is reviewed elsewhere,2-4 6418 and hence, this section presents some of the computational evidence without going into the computational details. The interested reader is advised to consult the above references. The evidence comes from two types of computational experiments , shown in Schemes... 

Singh, M., Berger, B., and Kim, P. S. (1999). LearnCoil-VMF Computational evidence for coiled-coil-like motifs in many viral membrane-fusion proteins./. Mol. Biol. 290, 1031-1041. 

Sarwar, G., Corsi, R., Allen, D. and Weschler, C. (2003) The significance of secondary organic aerosol formation and growth in buildings experimental and computational evidence. Atmospheric Environment, 37, 1365-81. 

Pouget, F., M. Dacier, and V.H. Pham, On the Advantages of Deploying a Large Scale Distributed Honeypot Platform, to appear in the Proceedings of the E-Crime and Computer Evidence Conference 2005, Monaco, Feb. 2005. 

Ganapathisubramanian, N. and Noyes, Richard M., "A discrepancy between experimental and computational evidence for chemical chaos", to be published J. Chem. Phys. 

To summarize, we note that isolated interfaces within or between solids are regarded as structural faults, but that, in view of both experimental and computational evidence, it is often convenient to regard some structures as made up of regular sequences of stacking faults . 

Based on the computational evidence, it was concluded that the associated ultrafast ET reaction for the [FBC/Q]- bioexciplex can essentially be seen as a... 

Clemente FR, Houk KN (2004) Computational evidence for the enamine mechanism of intramolecular aldol reactions catalyzed by praline. Angew Chem Int Ed Engl 43 5766-5768... 

Unlike the cation radicals of aromatic molecules, the anion radicals do not form stable dimer anion radicals, presumably due to an increase in electron-electron repulsion [42]. To our knowledge, there is no experimental or computational evidence for stabilization of nucleobase anion radicals upon r-stacking in duplex DNA. 

Density functional theory (DFT) and post-Hartree-Fock MP2 in conjunction with the B3LYP employing the 6-31G(d) basis set were used to predict structure and correlate assignments of the fundamental vibrational modes of 3/7-1,2-dithiole-3-one la and 3/7-1,2-dithiole-3-thione lb with experimental data <1998VSP77>. These sulfur-rich heterocycles, characterized by a long and weak S-S bond, are represented in accordance to the simple 7t-MO theory by resonance contributor 8, involving a cationic 67t-l,2-dithiolylium part and an anionic thiolate or olate part, and the exocyclic C=S bond is more delocalized than the C=0 bond. However, computational evidence suggests structures with localized bonds and relatively low aromatic delocalization, which is also supported by the low values of the dipole moments, that is, 3.54 D for la and 4.12 D for lb. 

Yamaguchi, K., Yabushita, S., Fueno, T., Houk, K. N. Mechanism of photooxygenation reactions. Computational evidence against the diradical mechanism of singlet oxygen ene reactions. J. Arrr. Chem. Soc. 1981, 103, 5043-5046. 

To recapitulate what we have discussed so far, we emphasize that three major bonding effects underlie the interaction between the gold clusters Au3 and Au4 and water oligomers. They are the anchor Au-O bonding, the nonconventional O-H Au hydrogen bonding, and the activation of the adjacent O-H bond. We provide a computational evidence that the formation of the donor-acceptor coordinative (anchor) bond Au-O in the studied complexes is a necessary prerequisite (but not sufficient) to the formation of the nonconventional hydrogen bond and to the activation of the adjacent O-H bond, and therefore this bond dominates the interaction mechanism. 

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