Conformation hydrogen bonding effect

Fluconazole was shown to be crystallizable in the form of a monohydrate and as a 1/4 ethyl acetate solvate, as well as a new nonsolvated form [56], In the hydrate phase the water molecules were established as isolated sites, while the ethyl acetate molecules occupied constricted channels in its phase. In all of the structures, the fluconazole molecule adopted a common overall conformation, but one that was capable of some degree of flexibility. Hydrogen-bonding effects were deduced to be dominant in determining the structure of the different solvatomorphs. 

Figure 2. Extraction of anharmonicity constants ojexe from the comparison of fundamental OH stretching spectra (center) with overtone spectra (top) and OD spectra (bottom) for the case of jet cooled trifluoroethanol (M) and its most stable dimer conformation, which features a hydrogen bond donor stretching band (Dd) and an acceptor stretching band (Da). The deuteration analysis yields slightly different constants than the overtone approach and underestimates the hydrogen bond effect on donor stretching modes [89].

Finally the effects of conformation, hydrogen bonding and Lewis acids on the intramolecular electron transfer, spectroscopy and photochemistry of amides were recently studied174-176 (equations 119-121). 

By chance rather than by design, the third chapter in this volume also emanates from Israel. Bernard S. Green, Rina Arad-Yellin, and Mendel D. Cohen have surveyed organic reactions in the solid state from the standpoint of the stereochemist. In the first part of the chapter, the authors discuss the stereochemical consequences of the crystallization of conformationally mobile systems. Conformational, crystal-field, and hydrogen-bonding effects, among others, are responsible for the selective crystallization of stereoisomers that may not be dominant in solution. The second part of the chapter is concerned with the stereochemical consequences of chemical, and especially photochemical, reactions in the solid state. 

A phenomenon which must be accounted for in many conformational problems is that of the hydrogen-bonding effect. The general steric, non-bonded interaction potential functions and the electrostatic potential approximations do not, intrinsically, correctly account for the special properties encountered in... 

For 13C NMR studies, the intermolecular effects which can affect chemical shifts have been documented (25). These are of two types hydrogen-bonding effects and conformational or y effects. 

The somewhat different a/s ratios for 47 and 48 account for the curviture noted by Dimroth and co-workers when they plotted r(47) against r(48). Also, the relative a and s values in Equations 110 and 111 appear to conform with an observation we have made in other correlations, that is that sterically insulating a chromophore from its cybotactic environment seems to lessen nonspecific polarity effects to a greater extent then specific hydrogen-bonding effects. 

In the case of bromate salts, the structure was symmetrical with a point group. Calculations to minimize the conformation using the input coordinates of the observed structure gave a rather than the expected symmetry, which was due to rotations about the Ln-Op bonds as well as to hydrogen-bonding effects (Hay 1991). 

Although the calculated variation in J(N=C), as a function of e, is not large, it is comparable to the J(N-C) data for aniline and formaraide which is attributed to specific hydrogen bonding effects. Thus, the nonspecific influences, included in the solvaton model, could be as important as hydrogen bonding, and perhaps conformational effects, on J(N=C). 

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