In conformational analysis

M. Robb, M. Garavelli, M. Olivucci, and F, Bernardi, in Reviews in Computational Chemistry, K. Lipkowitz and D. Boyd, eds., Vol. 15, John Wiley Sons, New York, 2000, pp. 87-146. M. Olivucci, M, Robb, and F. Bernardi, in Conformational analysis of molecules in excited states, Wiley-VCH, New York, 2000, pp. 297-366. 

As we have discussed, a common strategy in conformational analysis is to perform two-stage process involving first, the generation of a large number of minimum enerj... 

K. Rasmussen, in G. Berthier and co-workers, eds., Eecture Notes in Chemisty, Vol. 27, Potential Energy Functions in Conformational Analysis, Springer-Vedag, Berlin, 1985. 

The same inversion occurs in the case of the trans isomer . Changes in conformational properties when passing from the neutral to the corresponding radical anion is a recent and well-documented topic in conformational analysis ". ... 

Masamura.M. 1988a. Reliability of AMI in Conformational Analysis of Unionized Amino Acids. J. Mol. Struct. (Theochem) 168, 227-234. 

M. Olivucci, M. Robb, and F. Bernardi, in Conformational analysis of molecules in excited states, Wiley-VCH, New York, 2000, pp. 297-366. 

The energetically favorable conformations of model alkyl nitronate (88) and related compounds (89 to 91) (283) were determined by the B3LYP/6-31G(d) method (see Chart 3.9). It appeared that the marked conformations with the minimized dipole moments are energetically most favorable for compounds (88-91) (the use of the dipole-dipole interaction model in conformational analysis was also described in the publication (284)). Calculations including n-n interactions (see Fig. 3.1) did not change this situation because the contribution of this effect is equal in magnitude for both limiting conformations shown in Chart 3.9. 

Bucourt, R., The Torsion Angle Concept in Conformational Analysis, 8, 159. 

Hofer, O., The Lanthanide Induced Shift Technique Applications in Conformational Analysis, 9, 111. 

One example of the use of 2D-NMR experiments in conformational analysis is the study of molecular interactions between cinchonidine and acetic acid [26]. These alkaloids are used as chiral auxiliaries in enantioselective hydrogenations, and the enantiomeric excess is dependent on solvent polarity, acetic acid being a good solvent This suggests that protonation and a preferred conformation play a role in achieving high enantioselectivities. With a combination of COSY-experiments, 3J coupling constants and NOESY experiments, it was shown that one conformer is preferred in acidic solutions. 

The last section is a compilation of useful empirical additivity rules for 13C chemical-shift prediction, regardless of underlying transmission mechanisms. Peculiarities of less common substituents are cited, and, finally, substituent-induced 13C signal shifts in various cyclic compounds are discussed, with special emphasis on their use in conformational analysis I do not, however, claim completeness for this latter discussion. 

Since carbocations are structurally similar to ketones, they are discussed here. Schleyer s force field incorporates carbocation parameters, and Harris is exploring their application in conformational analysis (188). The calculated angles in a series of rigid polycyclic carbocations correlated well with ketone infrared frequencies (188a). The calculated relative stabilities among various conformers of tertiary cations of methylcyclohexane, methylcycloheptane, and methyl-cyclooctane do not contradict the limited MNR observations of these species at low temperature (188b). 

Lanthanide-induced Shift Technique - Applications in Conformational Analysis/Hb/er 9 111... 

Scalar couplings encode geometry and electronegativity. However, whilst the causes of variation in scalar couplings are known, precise prediction is not possible. It is therefore true that in most situations, it is possible to extract scalar couplings more precisely than it is to predict them. This does not render them valueless, indeed information can be inferred in conformational analysis. 

H, F). There are only a few examples of this long-range coupling their use in conformational analysis seems to be negligible. 

Rasmussen, K. Potential Energy Functions in Conformational Analysis Lecture Notes in Chemistry, Vol. 37 Springer-Verlag Berlin, Heidelberg, New York, Tokyo, 1985. 

These same considerations were expressed in a manner only seemingly different by Corradini (47, 48), who introduced a representation widely used in conformational analysis of vinyl polymers. He defined the chain bonds adjacent to the tertiary carbon atom as or — according to the clockwise or counterclockwise sequence of the two substituents in the Cahn-Ingold-Prelog sense, as shown in 8 and 9, as one proceeds along the chain. 

Ab initio calculations at the MP2 level of theory of a collection of substituted 1,3-dioxanes, 1,3-oxathianes, and 1,3-dithianes have been employed to study both the position of the conformational equilibria and the validity of the Perlin effect <2005T7349>. The 7h,c coupling constant proved to be a valuable tool in conformational analysis both twist conformers, in addition to the chair and alternative chair forms, could be readily identified simply by comparing experimental Vh,c coupling constants to the corresponding calculated values in the particular forms. In addition, the Perlin and reversed-Perlin effects of the C2-H fragments, c in 1,3-dioxanes,... 

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