The effects of the correlation between vibration and rotation of partially oriented molecules on the N.M.R. parameters

Lounila, Juhani; Diehl, P.

doi:10.1080/00268978400101591

Cited by 79 publications

(46 citation statements)

References 18 publications

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“…͑1͔͒. Assuming that the ring structure of styrene is solvent independent, as found for benzene, 23 the values of proton coordinates can be obtained from a simultaneous fit to the values of the intraring D i j of C1 and C2 isotopomers of styrene in I35 and ZLI 1132. The use of the data from both the liquid crystals provides extra independent equations to the fitting procedure, making more reliable the structure obtained.…”

Section: B Geometry Of the Phenyl Ringmentioning

confidence: 99%

“…In the calculations by the AP method the location of the Gaussian functions is allowed to vary, but the values of D i j (vib) are still those calculated with 0 as 27°. The calculations proceeded again by fitting four data sets simultaneously ͑24 couplings for each isotopomer in each phase͒, varying aa (R), bb (R)Ϫ cc (R), CH (R), and CC as phase and isotopomer-dependent variables, 0 and h as only phase dependent, and the bond distance r 23 and angles ␣ and ␤ as identical in all phases and for each isotopomer. The results are given in Table VI, and Fig.…”

Section: ͑18͒mentioning

confidence: 99%

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Is styrene planar in liquid phases?

Celebre

Longeri

et al. 2004

The Journal of Chemical Physics

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The proton NMR spectra of two 13 C-labeled isotopomers of styrene dissolved in two liquid crystalline solvents have been obtained and analyzed to yield four sets each of 24 dipolar couplings. These couplings were then used to investigate the structure of the ring and the ene fragments of the molecule, and the position of the maximum, 0 , in the ring-ene bond rotational probability distribution. To do this, the effect on the dipolar couplings of small-amplitude vibrational motion was taken into account using vibrational wave functions calculated by molecular orbital and density functional methods. It is concluded that the NMR data are consistent with the ring fragment, averaged over the ring-ene rotation, planar, while the ene fragment is not. The value of 0 is found to be 18.0°Ϯ0.2°for the two solutions, compared with a value of 27°calculated by the molecular method MP2/6-31G*.

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Section: B Geometry Of the Phenyl Ringmentioning

confidence: 99%

Section: ͑18͒mentioning

confidence: 99%

Is styrene planar in liquid phases?

Celebre

Longeri

et al. 2004

The Journal of Chemical Physics

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“…Except for rotations about C-C bonds that are at the root of conformer changes, our treatment neglects non-rigid effects such as molecular vibrations [37][38][39] and interactions between these vibrations and molecular reorientations. [40][41][42] Both nonrigid effects have been shown to make significant contributions to dipolar couplings. For example, the splittings observed in the 1 H NMR spectrum of methane as solute in nematic solvents 43 are a dramatic example of the effect of vibrationreorientation interaction.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

A model-free temperature-dependent conformational study of n-pentane in nematic liquid crystals

Burnell

Weber

Dong

et al. 2015

The Journal of Chemical Physics

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The proton NMR spectra of n-pentane orientationally ordered in two nematic liquid-crystal solvents are studied over a wide temperature range and analysed using covariance matrix adaptation evolutionary strategy. Since alkanes possess small electrostatic moments, their anisotropic intermolecular interactions are dominated by short-range size-and-shape effects. As we assumed for n-butane, the anisotropic energy parameters of each n-pentane conformer are taken to be proportional to those of ethane and propane, independent of temperature. The observed temperature dependence of the n-pentane dipolar couplings allows a model-free separation between conformer degrees of order and conformer probabilities, which cannot be achieved at a single temperature. In this way for n-pentane 13 anisotropic energy parameters (two for trans trans, tt, five for trans gauche, tg, and three for each of gauche + gauche + , pp, and gauche + gauche − , pm), the isotropic trans-gauche energy difference E tg and its temperature coefficient E ′ tg are obtained. The value obtained for the extra energy associated with the proximity of the two methyl groups in the gauche + gauche − conformers (the pentane effect) is sensitive to minute details of other assumptions and is thus fixed in the calculations. Conformer populations are affected by the environment. In particular, anisotropic interactions increase the trans probability in the ordered phase. C 2015 AIP Publishing LLC. [http://dx

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“…The effects of the coupling between vibrational and reorientational motion on the determination of molecular geometries have been investigated by very few, specialized studies of highly symmetric "rigid" molecules [23,24] and, very recently, for the "flexible" ethane molecule. [25] The influence of the coupling on the calculated bond-length and angle values is small as far as high frequency vibrational modes are involved (the "rigid" molecule case), but could play a significant role in flexible molecules where large amplitude motions are present.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…The first minimum, corresponding to the most-abundant conformer, is used to derive the covariance matrices of Equa-tion (24) to calculate the vibrational corrections for the "ene" dipolar couplings. Since the s-trans conformer is by far the most abundant, the approximation used is expected to be without consequences; so, the small observed differences between the geometries of the averaged "ene" fragment and the values calculated for the whole molecule are likely to be due to the minimization process rather than a consequence of this approximation.…”

Section: Optimization Of the "Ene" Fragmentmentioning

confidence: 99%

Intrinsic Information Content of NMR Dipolar Couplings: A Conformational Investigation of 1,3‐Butadiene in a Nematic Phase

Celebre

Concistrè

et al. 2006

ChemPhysChem

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The conformational equilibrium of 1,3-butadiene in a condensed fluid phase is investigated by liquid-crystal NMR spectroscopy. The full set of D(HH) and D(CH) dipolar couplings is determined from the analysis of the (1)H spectra of the three 1,3-butadiene most-abundant isotopomers (i.e. the all (12)C and the two single-labeled (13)C isotopomers) for a total of 21 independent dipolar couplings. A very good starting set of spectral parameters for the analysis of the (1)H spectrum is determined in a semiautomated way by the analysis of the (N-1) (specifically, N=6, the number of 1/2 spin nuclei in the spin system) quantum refocused (5QR), and not (5Q), spectra. As an alternative approach, a Monte Carlo (MC) numerical simulation, capable of predicting the solute ordering, is tested to simulate the 5QR spectrum. The set of D(ij) couplings is very good, proving that the MC method can represent a novel, valid alternative to the existing spectral simplification procedures. The experimentally determined dipolar-coupling data set is fully compatible with the 1,3-butadiene conformational distribution reported in the literature for isolated molecules, indicating the presence of about 99 % of s-trans conformer. With regards to the remaining 1 %, in spite of the direct and very strong dependence of the observables on the molecular structure, it was not possible to discriminate between the planar s-cis and s-gauche forms, both of which produce a very good fit of the dipolar couplings. Vibrational corrections, up to the anharmonic term, were applied; the calculated geometrical parameters are in good- although not exact-agreement with those reported in the literature from experimental and theoretical investigations. This result can be considered as supporting the methodology used for obtaining the structure and conformational distribution of a flexible molecule in a liquid phase.

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The effects of the correlation between vibration and rotation of partially oriented molecules on the N.M.R. parameters

Cited by 79 publications

References 18 publications

Is styrene planar in liquid phases?

Is styrene planar in liquid phases?

A model-free temperature-dependent conformational study of n-pentane in nematic liquid crystals

Intrinsic Information Content of NMR Dipolar Couplings: A Conformational Investigation of 1,3‐Butadiene in a Nematic Phase

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