Generalized torsional angle

Poirrette AR, Willett P. Pharmacophoric pattern matching in files of three-dimensional chemical structures characterization and use of generalized torsion angle screens. J Mol Graph 1993 11 2-14. 

Let us assume that system 0 can be transformed to system 1 through the continuous change of some parameter A defined such that Ao and Ai correspond to systems 0 and 1, respectively. This parameter could be a macroscopic variable - viz. the temperature, a parameter that transforms J o to -A j, or a generalized coordinate (e.g., a torsional angle or an intermolecular distance) that allows the different structural states of the system to be distinguished. It follows that ... 

The conformation of the chains of isotactic polymers in the crystalline state is generally helical and corresponds to a succession of nearly trans and gauche torsion angles, the exact values depending on the bulkiness of the side groups. Molecular mechanics calculations have been extensively used for the prediction of the chain conformation of polymers in the crystal.29... 

Calculations of the conformational energy are performed according to the equivalence principle and, as a consequence, a succession of backbone torsion angles. .. 0i020i 20i 2- is generally assumed for isotactic polymers. 

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