Rotamer conformations

Rotamer conformation of the purine ring ax (0 = 15-59°) because of weak intramolecular hydrogen bonding. 

One last example in this section is the observation that for a particular OC-6 Co(III) complex, an atropisomer with rotamer conformation can be obtained as the diaster-eomeric trans- CoC12py4 (hydrogen L-dibenzoyltartrate) compound in solid powder, but in solution the racemization is too fast to observe the CD spectrum.48... 

The preferred rotamer conformation of the XS02Y- radical series shows the usual intramolecular hydrogen-bond interaction which is characterized by the small dihedral angle a (rotamer h) for HOS020 (19), a = 23.2°, HSS020 (22), a = 37.0° and HOSQ2S-... 

Conformationally rigid n-glycosides were found to be inert toward ozone. Rotamers A-, 3. and A3 of an n-glycoside which correspond to conformers D, B , and E respectively of an acetal function are. consequently unreactive as predicted. Compound 160 can be considered a rigid model for the most stable rotamer (conformer ) of an n-glycoside and it was found unreac-... 

To help characterize the structure and function of dopamine receptors at the molecular level, the x-ray crystal structure of apomorphine (77) was compared to a structural model of dopamine ("Fig. 25.9k It is obvious that apomorphine contains molecular features In common with the structure of dopamine In the trans a-rotamer conformation ("Figs. 25.9 and 25. 0). Isoapomorphine, which embeds the structure of dopamine In the trans p-rotamerlc conformation ("Fig. 25.10k Is less active than apomorphine as a dopamine agonist. The... 

Different conformations (shapes) of the same molecule that are interconvertible by rotation around a single bond are called conformers or rotamers. Conformers are stereoisomers, isomers with the same atom connectivity but different spatial arrangements of atoms. 

Rotamers Conformational isomers that can be interconverted by rotation about one or more single bonds (e.g., gauche and anti butane). 

Secondly, we have not discussed in any detail the effects of nuclear motion. Methods used to calculate these vibrational corrections, for both zero-point vibrational effects and temperature effects, have been described elsewhere in this book. There are, however, other effects that should also be considered. We have not discussed the role of the purely vibrational contributions to molecular (electric) properties (Bishop 1990), which in certain cases can be as large as the electronic contributions (Kirtman et al. 2000). Moreover, in conformationally flexible molecules one has to consider the effects of large nuclear motions. For instance, for a proper comparison with experiment, it may not be sufficient to perform an ab initio calculation for a single molecular structure. In experiment one will always observe the average value of the different thermally accessible isomers (rotamers, conformers), and in order to allow for a direct comparison with these experimental observations, a Boltzmann average of the properties of these isomers must be computed. This is particularly important when the properties of the isomers are very different, possibly even differing in sign (Pecul et al. 2004). 

Isomers of diamond hydrocarbons (polymantanes) have been enumerated using graph-theoretical methods. Staggered rotamers (conformers) of linear and branched alkanes may also be enumerated. Interestingly, the numbers of isomers of benzenoids, polymantanes, and staggered n-alkane conformers are related with some restrictions. ... 

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