Conformational analysis of higher poly(oxyalkylenes) using empirical force field calculations

Miyasaka, Tsutomu; Yoshida, Takaichi; Imamura, Yosuke

doi:10.1002/macp.1986.021870620

Cited by 4 publications

(8 citation statements)

References 7 publications

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“…Besides the present study, only Miyasaka et al have reported explicit values for E χ ‘ ‘ , E χ ‘ , and E κ (see footnote f in Table ) for POM 3 . In close agreement, both studies find that E χ ‘ ‘ is small and positive while E χ ‘ is small and negative.…”

Section: Resultsmentioning

confidence: 53%

“…The energies listed in Table were all obtained from molecular mechanics calculations; hence it can be assumed that the E σ values do not reflect the extra stabilization of gauche states derived from the oxygen gauche effect. At the same time, the value E σ = −0.4 kcal mol -1 from Miyasaka et al . appears to factor in some portion of this observed effect.…”

Section: Resultsmentioning

confidence: 84%

“…The values of E ω for both POM 3 and PDMO vary considerably across the various studies. For POM 3 , the values range from 0.82 kcal mol -1 from ref to 2.36 kcal mol -1 from ref . The energy of this interaction appears to be sensitive to the choice of force field but not to the inclusion or exclusion of geometry optimization.…”

Section: Resultsmentioning

confidence: 97%

“…Rotation of the C−C bond in POM 3 and PDMO to a gauche conformation draws the O···CH 2 interaction into close proximity. Semiempirical force-field (molecular mechanics) calculations have found this interaction to be slightly attractive in both POM 3 and PDMO. − The van der Waals radius of the O atom is small (compared with the analogous CH 2 group in PE) to lessen steric repulsions, and the polarity of the C→O bond leads to an electrostatically attractive δ+ CH 2 ···O δ- interaction. Nevertheless, experimental evidence reveals that the C−C bond prefers gauche over trans even more than predicted on the basis of molecular mechanics calculations, by 0.4 kcal mol -1 in POM 3 , and by 0.3−0.7 kcal mol -1 in PDMO. ,, This preference is confirmed by the X-ray diffraction studies on POM 3 by Tadokoro et al, who identified ttgg as the most stable of three crystal modifications identified for the [−O−C−C−C] sequence.…”

Section: Introductionmentioning

confidence: 99%

“…Semiempirical force-field (molecular mechanics) calculations have found this interaction to be slightly attractive in both POM 3 and PDMO. [4][5][6][7] The van der Waals radius of the O atom is small (compared with the analogous CH 2 group in PE) to lessen steric repulsions, and the polarity of the CfO bond leads to an electrostatically attractive δ+ CH 2 ‚‚‚O δinteraction. Nevertheless, experimental evidence reveals that the C-C bond prefers gauche over trans even more than predicted on the basis of molecular mechanics calculations, by 0.4 kcal mol -1 in POM 3 4,8 and by 0.3-0.7 kcal mol -1 in PDMO.…”

Section: Introductionmentioning

confidence: 99%

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Conformational Characteristics and Unperturbed Chain Dimensions of the Oxygen-Containing Polymers [−OCH₂CR₂CH₂−]_n with R = H, CH₃, and CH₂CH₃

Welsh¹,

Abbassi²,

Galiatsatos³

et al. 1996

Macromolecules

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MM3 molecular mechanics calculations reveal that poly(3,3‘-diethyloxetane) (PDEO) differs sharply from poly(3,3‘-dimethyloxetane) (PDMO) and poly(trimethylene oxide) (POM3) in terms of conformational preferences, notwithstanding the similarity of these three polymers as successive members of the homologous series [OCH2CR2CH2] n where R = CH2CH3, CH3, and H, respectively. Within the four-bond repeat unit OCH2CR2CH2, POM3 and PDMO both prefer ttgg while PDEO prefers tttt. These conformational differences are reflected in the predicted values of the characteristic ratio CR = 〈r 2〉0/nl 2 for the unperturbed chain dimensions (after allowance for the oxygen gauche effect) obtained from rotational-isomeric-state (RIS) calculations: 3.9 for POM3, 4.7 for PDMO, and 23 for PDEO. These CR values for POM3 and PDMO are consistent with experiment (3.9 and 4.3, respectively) and with previous theoretical treatments. The larger R substituent of PDEO compared with PDMO and POM3 imposes steric demands that offset the otherwise strong preference of the C−C backbone bonds for gauche states. This reversal in preference from gauche to trans causes the abrupt increase in CR since now the almost exclusively all-trans backbone of PDEO lacks the distinctive conformational randomness of POM3 and PDMO. In terms of E σ = E t − E g for the focal C−C bond in these polymers, comparison of the MM2, MM3, and Discover (plus a variant Discover‘) force fields reveals a wide disparity of values for E σ and more so for the constituent energy components E stretch, E bend, E torsion, E vdW, and E electrostatics. The preference of the focal C−C bond in PDEO for trans over gauche involves a surprising degree of interplay among these energy components; hence the conformational analysis of PDEO would represent a stringent test of any existing or prospective force field.

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Section: Resultsmentioning

confidence: 53%

Section: Resultsmentioning

confidence: 84%

Section: Resultsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Conformational Characteristics and Unperturbed Chain Dimensions of the Oxygen-Containing Polymers [−OCH₂CR₂CH₂−]_n with R = H, CH₃, and CH₂CH₃

Welsh¹,

Abbassi²,

Galiatsatos³

et al. 1996

Macromolecules

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The conformations adopted by alkyl chains in α,ω-bis(aryl)alkanes in liquid-crystalline phases

Cheung¹,

Emsley²

1993

Liquid Crystals

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The conformations adopted by the alkyloxy chains in the u,~-bis(4-pheny1oxy)alkanes (PONOP) with 2, 3 and 4 methylene groups in the alkyl chain have been investigated for an isotropic solution in acetone for the compound with N = 2, and for samples dissolved in three nematic solvents for all three compounds.The energy difference, EEc, between gauche and trans conformers produced by rotation about the C-C bond in P 0 2 0 P dissolved in acetone was derived from the scalar coupling constants obtained by analysing the proton spectrum from molecules containing a 13C atom at one C, position. This gave EGc in the range -0.58 to 049 kJmol-'. The deuterium NMR spectra of fully deuteriated samples of the PONOP dissolved in the nematic solvents were used to obtain local order parameters from the quadrupolar splittings. These were compared with values calculated by the mean field method of Emsley, Luckhurst and Stockley (ELS) to give values of E F in the liquid-crystalline phases. The values obtained for Ecc change from being negative for P 0 2 0 P , through zero for P 0 3 0 P to 2.5 kJ mol for P 0 4 0 P . The deuterium NMR data obtained previously for the mesogenic molecules a,o-bis(4-cyanobiphenyloxy)alkanes in their nematic phases have been re-interpreted and it is shown that Egc in these compounds is also strongly dependent on chain length.

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The Model Compounds and Conformational Analysis of Poly(thiotrimethylene) Using Molecular Mechanics Method

Miyasaka¹,

Yoshida²

1988

Bulletin of the Chemical Society of Japan

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Several model compounds of poly(thiotrimethylene), including one to four thiotrimethylene units, were studied by means of a molecular mechanics method. The geometric and statistical weight parameters were directly derived from the results of molecular mechanics calculations concerning several conformers of these model compounds. Although the first-order interactions of poly(thiotrimethylene) were significantly larger than those of poly(oxyalkylenes), the second-order interactions of this polymer were much smaller. The “gauche effect” by sulfur atoms seemed to be mainly caused by small second-order interactions. By means of the model, compounds including more than three repeating units, the calculated configuration-dependent properties were in better agreement with the experimental ones than that calculated earlier. The better agreement was obtained by varying some of the geometric parameters. Compounds including more than three repeating units of the polymer were available as model compounds. Since this was also true in poly(oxyalkylenes), it was found that a combination of the methods of molecular and statistical mechanics was sufficiently effective to investigate the configurational properties of poly(thiotrimethylene).

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Conformational analysis of higher poly(oxyalkylenes) using empirical force field calculations

Cited by 4 publications

References 7 publications

Conformational Characteristics and Unperturbed Chain Dimensions of the Oxygen-Containing Polymers [−OCH₂CR₂CH₂−]_n with R = H, CH₃, and CH₂CH₃

Conformational Characteristics and Unperturbed Chain Dimensions of the Oxygen-Containing Polymers [−OCH₂CR₂CH₂−]_n with R = H, CH₃, and CH₂CH₃

The conformations adopted by alkyl chains in α,ω-bis(aryl)alkanes in liquid-crystalline phases

The Model Compounds and Conformational Analysis of Poly(thiotrimethylene) Using Molecular Mechanics Method

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Conformational analysis of higher poly(oxyalkylenes) using empirical force field calculations

Cited by 4 publications

References 7 publications

Conformational Characteristics and Unperturbed Chain Dimensions of the Oxygen-Containing Polymers [−OCH2CR2CH2−]n with R = H, CH3, and CH2CH3

Conformational Characteristics and Unperturbed Chain Dimensions of the Oxygen-Containing Polymers [−OCH2CR2CH2−]n with R = H, CH3, and CH2CH3

The conformations adopted by alkyl chains in α,ω-bis(aryl)alkanes in liquid-crystalline phases

The Model Compounds and Conformational Analysis of Poly(thiotrimethylene) Using Molecular Mechanics Method

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Conformational Characteristics and Unperturbed Chain Dimensions of the Oxygen-Containing Polymers [−OCH₂CR₂CH₂−]_n with R = H, CH₃, and CH₂CH₃

Conformational Characteristics and Unperturbed Chain Dimensions of the Oxygen-Containing Polymers [−OCH₂CR₂CH₂−]_n with R = H, CH₃, and CH₂CH₃