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11.
Several sophisticated methods to solution of symmetry specified enumeration problems are available in the modern literature.
In this paper we propose a simple technique that allows one to manually compute the exact numbers of fixed-symmetry derivatives
for a given structure either with inclusion or ignoring the substitution patterns. The basic idea of the method suggested
consists in the derivation of Pólya-like cycle indices for the automorphism groups of specially constructed orbit partition
graphs; the expansion of these indices and subsequent simple calculations result in the desired numbers of substituted derivatives
with achiral substituents. Limitations of the new technique (and a method suggested earlier) depend on the relevance of the
orbit partitions for particular subgroups of the point symmetry group. For illustration purposes, the results obtained for
the prismane (D
3h
) and adamantane (T
d
) structures are discussed. In the former case the numbers of substituted derivatives can be found for all subgroups of the
D
3h
group, whereas in the latter case these numbers can be determined for eight out of eleven subgroups of the T
d
point symmetry group.
This work is based on the text of the lecture presented by the authors at the 5th All-Russia Conference on Molecular Modeling
(Moscow, April 2007). The paper deals with the methodology and detailed treatment of applied aspects related to solution of
enumeration problems for substituted derivatives with prescribed symmetry groups. Unlike the known methods of symmetry specified
enumeration, the technique suggested is simple enough and may be regarded as generalization of the Pólya methodology, which
is widely used by chemists.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 227–245, February, 2008. 相似文献
12.
S. A. Patlazhan 《Journal of Polymer Science.Polymer Physics》1993,31(12):1649-1665
A statistical theory of light scattering from deformed isotropic and textured heterogeneous polymer materials is formulated. Two types of textured structures are analyzed: assemblies of optically isotropic and anisotropic rods and a spatially anisotropic distribution of isotropic spherical inclusion centers. The small-angle Hv light-scattering patterns are calculated. The appearance of scattering from isotropic rods and spheres in deformed materials has been demonstrated. The changes of the Hv scattering patterns as a function of elongation and strucuture parameters are discussed. © 1993 John Wiley & Sons, Inc. 相似文献
13.
14.
The complete proofs of Krein’s theorem on the spectral shift function and the trace formula are given for a pair of self-adjoint
operators such that either (i) their difference is trace-class or (ii) the difference of their resolvents is trace-class.
The proofs, essentially due to Krein, is based on Herglotz’s theorem on the boundary value of the analytic functions whose
imaginary part is non-negative on the upper half plane, and an almost optimal class of functions are obtained for which the
trace formula is valid. Also an alternative method based on Weyl-von Neumann’s theorem for self-adjoint operators, avoiding
the complex function theory and inspired by Voiculescu’s work, is given for the first case. Furthermore, some applications
of the spectral shift function have been discussed. 相似文献
15.
Ummadisetty Subramanyam Swaminathan Sivaram 《Journal of polymer science. Part A, Polymer chemistry》2007,45(2):191-210
Homopolymerization of octadecene‐1 at different reaction conditions has been studied. Significant chain running can be seen at higher polymerization temperatures. Interestingly, insertion of octadecene‐1 into a sterically hindered nickel‐cation/carbon (secondary) bond is observed. The microstructure of the polymer was established using NMR spectroscopy. The effects of chain running on polymer melting, crystallization behavior, and dynamic mechanical thermal properties were studied using DSC and DMTA. The extent of chain running (i.e., 2,ω‐, 1,ω‐enchainments) decreases with an increase in the carbon number of α‐olefins. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 191–210, 2007 相似文献
16.
John A. Mikroyannidis Larysa Fenenko Masayuki Yahiro Chihaya Adachi 《Journal of polymer science. Part A, Polymer chemistry》2007,45(20):4661-4670
Three new copolymers, namely poly(fluorenevinylene‐alt‐naphthalenevinylene) ( N ), poly(fluorenevinylene‐alt‐anthracenevinylene) ( A ) and poly(fluorenevinylene‐alt‐pyrenevinylene) ( P ), were synthesized by Heck coupling of 9,9‐dihexyl‐2, 7‐divinylfluorene with a polynuclear aromatic dibromide. The 9,10‐disubstituted anthracene was obtained exclusively for A while N and P were obtained as a mixture of two isomers with predominant the 1,4‐disubstituted naphthalene and 1,8‐disubstituted pyrene, respectively. The polymers were soluble in common organic solvents and decomposed above 370 °C. Their glass transition temperature increased from 58 to 110 °C by increasing the number of the phenyl rings of the polynuclear aromatic moiety. Rather high‐efficiency blue and blue‐greenish photoluminescence (PL) of these copolymers in solution was largely decreased in their films, indicating the presence of concentration quenching in the solid state. The OLED using these polymers demonstrated green EL in the case of copolymers N and A , and red EL in the P derivative with ηEL = 0.26–0.31%. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4661–4670, 2007 相似文献
17.
18.
Chin‐Ping Yang Yu‐Yang Su Sheng‐Huei Hsiao 《Journal of polymer science. Part A, Polymer chemistry》2006,44(20):5909-5922
Two series of novel fluorinated poly(ether imide)s (coded IIIA and IIIB ) were prepared from 2,6‐bis(3,4‐dicarboxyphenoxy)naphthalene dianhydride and 2,7‐bis(3,4‐dicarboxyphenoxy)naphthalene dianhydride, respectively, with various trifluoromethyl‐substituted aromatic bis(ether amine)s by a standard two‐step process with thermal or chemical imidization of the poly(amic acid) precursors. These fluorinated poly(ether imide)s showed good solubility in many organic solvents and could be solution‐cast into transparent, flexible, and tough films. These films were nearly colorless, with an ultraviolet–visible absorption edge of 364–386 nm. They also showed good thermal stability with glass‐transition temperatures of 221–298 °C, 10% weight loss temperatures in excess of 489 °C, and char yields at 800 °C in nitrogen greater than 50%. The 2,7‐substituted IIIB series also showed better solubility and higher transparency than the isomeric 2,6‐substituted IIIA series. In comparison with nonfluorinated poly (ether imide)s, the fluorinated IIIA and IIIB series showed better solubility, higher transparency, and lower dielectric constants and water absorption. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5909–5922, 2006 相似文献
19.
Mu Jie YANG Kuan LIU 《中国化学快报》2006,17(10):1381-1384
Since the early works of A. J. Heeger, A G. MacDiarmid and Hideki Shirakawa on semiconducting polymers, π-conjugated oligomers and polymers have been actively investigated for a variety of optoelectronic applications, such as field effect transitors (FET… 相似文献
20.