Quantum chemical PM‐3 study of the thermal stability of heterocyclic fragments of heteropolymers, 2. Six‐membered heterocycles

Зубков, В. И.; Yakimansky, Alexander V.; Bogdanova, Svetlana E.; Kudryavtsev, V. V.

doi:10.1002/mats.1994.040030218

Cited by 5 publications

(4 citation statements)

References 16 publications

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“…For that purpose, we shall assume that the microscopic particles interact among themselves through the harmonic spring (hs) or harmonic-oscillator-like potential e V given in Eq. (35), in which x j A0 are frequencies while d j A0 are some given ("bond") lengths. Then, the total quantum Hamiltonian is:…”

Section: Derivation Of Model Via Peierls' Variational Inequality and mentioning

confidence: 99%

“…[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] as samples of recent studies, not based upon Quantum Mechanics and to ref. [30][31][32][33][34][35][36][37][38][39][40] as examples of quantum mechanical ones. For a full variety of cases in Polymer Science, it may be not easy or, even, extremely difficult, to set up quantum-mechanical formulations: then, the probabilistic or Classical Mechanics approaches may well be the only available tools, in practice.…”

Section: Introductionmentioning

confidence: 99%

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Models of macromolecular chains based on Classical and Quantum Mechanics: comparison with Gaussian models

Alvarez‐Estrada¹

2000

Macromol. Theory Simul.

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of contentsFeature Article: Different approaches to the study of open linear freely-jointed (unhindered) threedimensional macromolecular chains at thermal equilibrium, based upon either Classical Hamiltonian Dynamics with constraints (namely, a formulation equivalent to Kramers' one) or Quantum Mechanics (with stiff harmonic springs), are reviewed and discussed in detail. Results from those approaches are compared to those arising from the standard Gaussian model. Fraenkel's approach, based upon Classical Mechanics (with stiff harmonic springs) and its comparison with the Gaussian model are also treated. It is argued that the quantum formulation is required in order that the treatment of the high-frequency vibrations be consistent. The role of the uncertainty principle is discussed, in support of the quantum-mechanical approach. At a later stage, internal rotations can be treated through Classical Statistical mechanics, under certain conditions. The quantum-Mechanics-based model appears to be consistent with the Gaussian model, while the one based upon constrained Hamiltonian Dynamics yields certain discrepancies with the latter. Classical and quantum-mechanical approaches to open linear freely-rotating (hindered) threedimensional macromolecular chains are also treated: the consistency of the quantum-mechanics-based model is displayed by deriving approximately the existence of a persistence length. It is argued that the possible advantages of the quantum-mechanical formulation should be expected not at large scales but at shorter ones. The specific topics to be treated are described in the summary of contents given below.Macromol. Theory Simul. 9, No. 2

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Section: Derivation Of Model Via Peierls' Variational Inequality and mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Models of macromolecular chains based on Classical and Quantum Mechanics: comparison with Gaussian models

Alvarez‐Estrada¹

2000

Macromol. Theory Simul.

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show abstract

“…The proof of Eqs. (30), (31), (32), (33) and (34) will be reported, in outline, in Appendix 2. For definiteness, we shall give below the explicit expression for T,, for N = 3:…”

Section: Functionmentioning

confidence: 99%

“…(43), (31),(32),(33), and(34) can be compared to the alternative quantum partition function, Z, , obtained issue of rotational invariance with another multiplicative potential V,,o, which, essentially, has the same properties and order of magnitude as V,. That is, V,,o does not contain any differential operator with respect to any angle, but it contains all terms of orderh z M .…”

mentioning

confidence: 99%

Hindered macromolecular chains: A quantum mechanical model

Alvarez‐Estrada

1998

Macromol. Theory Simul.

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A model for an open hindered three-dimensional macromolecular chain, based upon quantum mechanics, is proposed, which improves previous work. The chain is formed by N particles (so that all bond lengths between successive particles take on given values) and harmonic-like vibrational potentials in the high-frequency limit constrain all successive bond angles. This formulation leads, via a variational procedure and a suitable choice of variables, to a specific quantum Hamiltonian for the chain. Issues related to overall rotational invariance are clarified. Some properties of the resulting classical partition function are analyzed. Several checks of consistency are given.

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Quantum chemical PM‐3 study of the thermal stability of heterocyclic fragments of heteropolymers, 3. Thermal stabilities of different components of heteropolymer repeating units

Зубков

Bogdanova

Yakimansky

et al. 1995

Macro Theory & Simulations

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Dissociation energies (ED) of different components of repeating units of heteropolymers (HPs) have been calculated by the semiempirical PM-3 method. Comparison of ED values of heterocycles (HCs) and of single bonds contained in phenyl-substituted benzoheterocycles have shown that for polybenzazoles and HPs with carbonyl-containing HCs the initial degradation in the absence of weak links (uncyclized units, structural defects, etc.) preferably starts with HC homolytic decomposition. For these two groups of HCs the relationship between the E D of HCs and the initial degradation temperature of corresponding HPs is, on the whole, similar to the one found upon calculation of benzoheterocycles. In HPs based on quinoline and quinoxaline the single bond between HC and phenyl (Ph) group is less stable than the HC, and the breaking of that single bond can accompany the initial H P degradation. An analysis of relative stabilities of X-Ph bonds of Ph-X-Ph fragments of HPs with X = 0, S, CH,, CO and of the relationship between their stabilities and those of other fragments of the H P repeating unit has been performed by using both calculated ED values and those obtained from thermochemical data. ED values for Ph-X-Ph decompositions turned out to be close to those for some HCs.

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Quantum chemical PM‐3 study of the thermal stability of heterocyclic fragments of heteropolymers, 2. Six‐membered heterocycles

Cited by 5 publications

References 16 publications

Models of macromolecular chains based on Classical and Quantum Mechanics: comparison with Gaussian models

Models of macromolecular chains based on Classical and Quantum Mechanics: comparison with Gaussian models

Hindered macromolecular chains: A quantum mechanical model

Quantum chemical PM‐3 study of the thermal stability of heterocyclic fragments of heteropolymers, 3. Thermal stabilities of different components of heteropolymer repeating units

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