Rotational isomeric state model, conformational

W.L. Mattice and U.W. Suter, Conformational Theory of Large Molecules The Rotational Isomeric State Model in Macromolecular Systems, Wiley, New York, 1994. 

A very common approximation goes by the name of rotational isomeric state model (RIS). With such a model it is assumed that the molecular population is placed exclusively in a few energy minima, always according to the Boltzmann distribution. The conformations corresponding to the minima are called conformers, or rotational isomers, and are indicated by one or more letters (G, T) for butane three conformers are considered (G, T, G ), for pentane five (TT, G T, TG, G G, G G ). A more detailed examination of pentane reveals the existence of two further wells (fl, = 65 , 2 = 260° and 0, = 100°, 02 = 295°), sometimes indicated by G G and G G , respectively, close to the forbidden G G" conformation, but with a much tower energy (157, 158). 

Mattice WL, Suter UW (1994) Conformational theory of large molecules the rotational isomeric state Model in macromolecular systems. Wiley, New York... 

Mattice WL, Suter UW (1994) Conformational theory of large molecules The rotational isomeric state model in macromolecular systems, Wiley, New York Moritani T, Fujiwara Y (1973) J Chem Phys 59 1175 Nagai KJ (1959) J Chem Phys 31 1169 Nagai KJ (1962) J Chem Phys 37 490 Natta G, Corradini P, Ganis P (1962) J Polym Sci 58 1191 Suter UW (1981) Macromolecules 14 523 Viswanadhan VN, Mattice WL (1987) Macromolecules 20 685 Volkenstein M (1958) J Polym Sci 29 441 Volkenstein MV (1951) Dokl Akad Nauk SSSR 78 879... 

Quantitative determination of conformational disorder, in addition to assignments of the spectral features, requires accurate calibrations of relative absorptivities (extinction coefficients) for the various bands. These were calculated with the aid of the rotational isomeric state model of Flory (22), a statistical mechanical determination of conformational disorder in alkanes. The model requires an estimate for the energies of gauche bonds, chosen from the best available experiments to be 508 +/- 50 cal/mole, and an energy for the bond pairs E, chosen to be 3000 cal/mole. The... 

Figure 2 (a) Sketch of the variables determining the rotation isomeric state model of a statistical coil 9 = bond angle, = bond torsion angle [3], (b) Representation of one of the possible conformations of a two-dimensional statistical coil (33 monomers) with bond-angle restriction ( — 90° <0 <90°) [3],... 

The average dimensions, or other statistical properties of the polymeric chains, are then calculated, allowing for the relative probabilities of the rotational states and making full allowance for the mutual interdependence of adjacent pairs of bond rotational states. Parameters required for the models are normally obtained from molecular structure data and from experimental information relating to the statistical conformations of the polymeric chains. Further references to rotational isomeric state models will be made later. 

Eq. (6) with oji = 2x. A rotational isomeric state model for polyphosphate chains (2 76,187) was used to compute values of < rj >o required by Eq. (6). Comparison of the experimental values with the theoretical values, as well as with the values for the corresponding cyclic siloxanes (R(CH3)SiO)x [see Section III.(A)5] stronj y supports the contention that polyphos diate chains in sodium phosphate melts adopt random-coil conformations. Further evidence for the structure of sodium phosphate melts would come from precise data for macrocyclic concentrations in quenched sodium phosphate ring-chain equilibrates, if these became available. 

Chain models capture the basic elements of the amphiphilic behaviour by retaining details of the molecular architecture. Ben-Shaul etal [ ] and others [61] explored the organization of the hydrophobic portion in lipid micelles and bilayers by retaining the conformational statistics of the hydrocarbon tail within the RIS (rotational isomeric state) model [4, 5] while representing the hydrophilic/hydrophobic interface merely by an... 

W. L. Mattice and U. W. Suter, Conformational Theory of Large Molecules The Rotational Isomeric State Model in Macromolecular Systems, John Wiley Sons, Inc., New York, 1994. P. X Hory and D. Y. Yoon, X Chem. Phys 63,5358 (1974) D. Y. Yoon and P. X Hory, J. Chem. Phys 63,5366 (1974). 

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