Rotational isomeric states scheme

R 9 Y. Sasanuma, Intramolecular Interactions of Polyethers and Polysulfides, Investigated by NMR, Ab Initio Molecular Orbital Calculations, and Rotational Isomeric State Scheme An Advanced Analysis of NMR Data , p. 213 Vol. 50, 2003... 

Sasanuma, Y., Conformational analysis of chain molecules in liquid crystalline phases by a rotational isomeric state scheme with maximum entropy method I. H— H dipolar couplings from n-alkanes dissolved in a nematic solvent, Polym. J., 32, 883-889 (2000a). 

Sasanuma, Y., H. Kato, and A. Kaito. 2003. Conformational analysis of poly(di- -butylsilane), poly(di-M-hexylsilane), and poly(methyl- -propylsilane) by a rotational isomeric state scheme with molecular dynamics simulations. J Phys Chem B 107 11852. 

Table 1.5 summarizes the studies on cyclics of poly(di-methyl siloxane) and derivatives, and Table 1.6, those of other polymers. In these tables, refers to the molar cyclization equilibrium constant and RIS, to the rotational isomeric state scheme to analyze chain conformations. 

The chain-length dependence of the characteristic ratio, when the degree of polymerization is below the asymptotic limit, can also be modeled with fewer parameters than are needed to implement the rotational isomeric state scheme. The local details of tire chain structure can be characterized by a unique parameter. The persistence length a can be calculated from the backbone bond vectors as ... 

Conformational Analysis.— The major effort in this area has been directed towards empirical correlations of chemical shift and conformation. Tonelli and co-workers have examined the stereosequence dependence of C chemical shifts in polypropylene (PP) poly(vinyl chloride) (PVC), and polystyrene (PS) using the rotational isomeric-state scheme of polymer statistical mechanics. The structural variation of C shifts was shown to correlate well with the occurrence of three-bond gauche (y) interactions between carbon atoms together with y interactions between carbon and chlorine atoms in PVC and ring-current shifts in PS. It has been... 

Flory reviewed in 1969 the development and applications of the rotational isomeric state scheme calculations, which allow, by matrix algebra, the statistical mechanical averaging over the rotational states of chain properties which may be expressed as a vector or tensor quantity associated with the chain bonds, and estimations of the probabilities of chosen conformational sequences. The methods were generalized and schemes for reducing the dimensions of certain generator matrices were presented in 1974, when comparisons were also made with an alternative Fourier expansion method, currently in use for atactic polypropylene. These techniques have greatly contributed to an understanding... 

The configuration partition function, representing the sum of all such factors, one for each conformation of the chain as represented by the scheme of rotational Isomeric states, is... 

The level scheme of 99Y has been studied both through the B decay of 99Sr [PFE81,JPET85] and via an isomeric state at 2142 keV with high spin which is directly populated in fission [M0N82,MEY85]. This nucleus contains the most extended rotational band which has been found in an odd-A nucleus at A 100. In addition, several side bands have been observed. 

Acyl-2-nitroenamines (554) with = R can exist in four planar isomeric forms (Scheme 16) due to restricted rotation around the C(1)=C(2) and Q2)—C(3) bonds. The combined use of IR and NMR spectroscopy provides a complete picture of the isomeric equilibria of these compounds. Quantum-mechanical calculations of the structure, relative energies, solvation and vibrational spectra of a series of model 2-acyl-2-nitroenamines have confirmed the structural assignment of the isomers either in solution or in the pure state. 

It is easy to list the various chemical and biological events influenced by flexibility, but unfortunately efforts to quantitate this structural attribute have been few. Mann analyzed the conformation of alkanes by modifying the number of gauche arrangements with Pitzer s steric partition function. Luisiranked alkanes on a. scale of conformational rigidity based on three-states rotational isomerism. Unfortunately, these schemes are designed for acyclic hydrocarbons and have no inherent capability to be adapted to heteroatomic molecules. 

More recently, Tokumaru and collaborators found that the O-methyl ether of an aromatic ketone oxime, 2-acetylanthracene oxime O-methyl ether, upon irradiation in benzene underwent one-way Z, -isomerization through a quantum chain process in the triplet state (Scheme 7). The kinetics of the triplet-state isomerization and the potential energy surface of the triplet state were studied by transient spectroscopy. A quantum yield as high as 22 at a concentration of 1.35 x 10 M was obtained. According to their calculation, the Tj potential-energy curves of the substrate are in agreement with the rotation mechanism for one-way isomerization. ... 

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