Rotamers definition

NMR spectral analysis did not yield a definitive answer because of complications caused by limited sample mass, contaminants present in the sample, and most significantly, a rotamer effect arising from two separate amides. This gave rise to very complex NMR spectra that were not easily interpreted. In this study, the structure of the impurity was based on the LC/MS/MS data only. 

Scheme 3 Definition of hydroxyl rotamers about the C3-03 bond. The 0 torsion angle is defined by the corresponding H-Ci-O—Hi angle.

A detailed study was carried out on the radical anion derived from (10c) (Table 2) in connection with the conformational analysis of heteroaromatic carbonyl compounds. Notably different ESR signals could be observed originating from distinct rotational isomers. Unfortunately no information on the interconversion of the rotamers of (10c) could be definitely derived since these radicals were highly unstable at the temperature necessary for interconversion <74JCS(P2)562>. 

A folded protein could have a set of different conformations, thus we have here a first definition of a protein structure the global structure is a coininnation of sub-structures or conformations. The interconversion between them is not too fast. Each conformation is rigid and has a definite specific structure. This model is known as the rotamers modd. 

In treating substituent effects in different molecular classes one relies essentially on the transferability of ligand qualities and bond properties that is, one assigns an intrinsic (scalar) point property group dipole moment to a bond R—C. Both these qualities are characterized by definite numbers and disregard different rotamer populations of the substituents in the various molecular classes. 

Figure 11.2 (a) The mechanism of the iodolactonization of diastereomeric allylic fluorides via the most stable rotamers of the l -alkene x-complexes. (b) definition for the inside, outside, and anti positions and relative energies for the corresponding rotamers of fluoromethyl-substituted iodonium ion. 

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