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Conformational characteristics of polymeric chains with various degrees of rigidity

Ocampo M. A., Castano V. M.

Polimery

2000

T. 45, nr 11-12

771-774

A simple model based only on steric constrictions of chain molecules is used to describe the conformational characteristics of polymer chains endowed with various degrees of rigidity. The effect of rigidity of bond rotations was studied in terms of the model in relation to chain molecule size; a rigidity criterion was thus obtained, based on the width of the interval of rotational angles. Other results suggested the scaling law between the size of the chain and the number of monomers to become modified with the degree of chain rigidity. Examples of scaling behavior are discussed. An additional parameter, helicity, which corresponds with the average rotation angle, is presented as helpful in understanding the structural characteristics of polymer chains.

Do opisu charakterystyk konformacyjnych łańcuchów o różnych stopniach sztywności zastosowano prosty model oparty jedynie na sferycznych ograniczeniach łańcuchów polimerowych. Za pomocą tego modelu scharakteryzowano wpływ sztywności obrotów wiązań w zależności od wymiarów łańcuchów, uzyskując przy tym kryterium sztywności związane z szerokością przedziału kątów rotacji. Stwierdzono, że stopień sztywności łańcucha wpływa na postać prawa skalowania, które wiąże wymiar łańcucha z liczbą jednostek monomerycznych. Przedyskutowano przykłady dotyczące prawa skalowania. Wprowadzono dodatkowy parametr - helikalność - związany ze średnim kątem rotacji, upraszczający opis charakterystyki strukturalnej łańcuchów polimerów.

Współczesne postępy w wybranych aspektach chemii spiranów

Jamrozik J., Schab S.

Wiadomości Chemiczne

1998

[Z] 52, 3-4

269--281

The chemistry of spiranes has been studied extensively from many points of view and has already been the subject of many papers. Generally the spiranes are not a new class of compounds in the chemical sense, but they retain the chemical properties of their parent moieties. Much interest has been focused on the bonding character of the central spiro-atom. This review describes all aspects of spirane chemistry that have been developed in the last few years:spiroconjugation, helical structure, conformational transmission, photochromism and biologically active spiranes. When two perpendicular p systems are joined by a common tetrahedral atom, it is postulated that electronic delocalization will produce important and characteristic effects in the electronic spectrum [10, 11] and in chemical reactivity [14, 15]. This special case of homoconjugation has been called spiroconjugation (Schemes 1, 2). The presence of hypochromism suggests that the dominant conformation of spiranes is helical (Schemes 4, 5), [20-23]. The effect of conformational transmission in the series of new spirane systems was studied with the aid of 1H-NMR spectra (Schemes 7, 8), [36-38]. The photochromic behaviour of spiropyrans is based on the reversibility between the colourless 'closed' spiropyran from and the coloured 'open' merocyanine dye via heterolytic cleavage of the spiro oxygen-carbon bond (Scheme 9), [47, 48]. The spiropyrans and related compounds (spirooxazines) continue to arise a strong interest in various fields such as: non-silver high resolution photography [45], optical devices and holographic systems [46]. Many representatives of spiranes have a useful biological activity (Schemes 10, 11), [49-55]. For example 1,7-dioxaspiro[5.5]undecane is the major component of the sex pheromone of the olive fruit fly [56]. The purpose of this article is to show a 'phenomenon' of the spiro-atom and to present the most representative examples.