Characterisation of the structure, deuterium quadrupolar tensors, and orientational order of acenaphthene, a rigid, prochiral molecule, from the NMR spectra of samples dissolved in nematic and chiral nematic liquid crystalline solvents

Merlet, Denis; Emsley, J. W.; Jokisaari, Jukka; Kaski, Jaakko

doi:10.1039/b106069b

Cited by 25 publications

(52 citation statements)

References 7 publications

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“…It is noted that (i) according to the inversion symmetry properties of the coupling coefficients in eqs (2.6) and (2.10), inverting the chirality of the solvent has no effect on (2) (2) 02 , uu but inverts the sign of () With the numbering used in Figure 2, the enantiotopic deuterium pairs are {D19, D20} and {D21, D22} while the two pairs are related by a twofold rotation about the z axis and therefore the spectra of D19 and D21 are identical and so are those of D20 and D22. The relevant geometrical constants can be evaluated directly from the known geometry of the molecule [14]; these are 20 19 0.166 20 20 19 19 0.782 20 19 0.154…”

Section: Acenaphthenementioning

confidence: 99%

Molecular Interactions in Chiral Nematic Liquid Crystals and Enantiotopic Discrimination through the NMR Spectra of Prochiral Molecules I: Rigid Solutes

2016

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We have developed a molecular theory for enantiotopic discrimination in prochiral solutes dissolved in chiral nematic solvents by means of NMR spectroscopy. The leading rank tensor contributions to the proposed potential of mean torque include symmetric as well as antisymmetric terms with respect to spatial inversion; these lead to consistent determination of all prochiral solute symmetries for which enantiotopes are distinguishable by NMR and also to excellent quantitative agreement when tested against the available experimental data for the rigid solutes acenaphthene and norbornene as well as for the moderately flexible ethanol molecule.

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Section: Acenaphthenementioning

confidence: 99%

Molecular Interactions in Chiral Nematic Liquid Crystals and Enantiotopic Discrimination through the NMR Spectra of Prochiral Molecules I: Rigid Solutes

2016

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“…When, as usually happens, these data are not available from experiments, quantum-mechanical calculations can be used to provide reliable estimates of both quantities. [17,18,[27][28][29] Theoretical Calculation of the Force Field: The F used in the ensuing calculations was obtained with the density functional theory (DFT) method using the three-parameter Becke-Lee-Yang-Parr (B3LYP) exchange-correlation functional [30,31] and the 6-31G* standard Gaussian basis set. [32] The corresponding geometry was optimized after imposing planarity on the heavy-atom skeleton by constraining all the dihedral angles and the C=O fragment.…”

Section: Methodsmentioning

confidence: 99%

“…28 in the covariance matrix elements and using the geometry values given in column II of Table 5 for the phenyl ring and that of Table 4 for the acetyl moiety. Repeating the same calculations using the geometry values given in column I and including all the vibrational frequencies, a low RMS (0.33 Hz) was obtained with a too long r C5C8 = 1.586 AE 0.001 and a too small ff C5C8C9 = 110.9 AE 0.58.…”

Section: Structure Of the Heavyatom Skeleton Using The Rotational Isomentioning

confidence: 99%

NMR Spectroscopy Investigation of the Cooperative Nature of the Internal Rotational Motions in Acetophenone

Longeri

Pileio

et al. 2005

ChemPhysChem

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The proton NMR spectrum of the doubly enriched acetophenone-carbonyl,methyl-13C2 isotopomer dissolved in a liquid-crystalline solvent (LXNMR) was analyzed to yield a data set of 19 dipolar couplings. The presence of so many couplings, and in particular the dependence of some of them on the acetyl carbons enabled the investigation of the structure of the acetyl moiety and of possible cooperative motions about the aryl-carbonyl and carbonyl-methyl bonds. Methodological aspects, and approximations relating to the application of the vibrational correction procedure in the presence of large-amplitude torsional motions, are discussed. Results show that it is possible to discriminate between a continuous and a discrete conformer distribution about the angle phi(1) but not among a few proposed continuous shapes of U(iso)({phi}). In this study, the use of dipolar couplings with a non-negligible contribution from the indirect spin-spin coupling tensor J, (D(C8C9) in our case), for structural determination is extended from rigid to flexible molecules. The 1/2J(aniso)(C8C9) contribution was derived theoretically using the density functional theory linear response (DFT-LR) first-principles calculation of the J(C8C9) spin-spin coupling tensor.

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“…Even theoretical approaches at a relatively low level of approximation can be considered sufficiently precise for our purposes, since the vibrational corrections are usually smaller than 5 % of the dipolar couplings. [36][37][38] The precision should increase with the level of approximation and basis set used; for this reason, we opted for MP2/6-31G* for 1,3-butadiene, as a reasonable compromise between CPU time and accuracy. Moreover, we found [39] that at least for benzene, more accurate results were obtained if experimental vibrational frequencies, rather than the calculated ones, were used.…”

Section: Vibrational Averagingmentioning

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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Characterisation of the structure, deuterium quadrupolar tensors, and orientational order of acenaphthene, a rigid, prochiral molecule, from the NMR spectra of samples dissolved in nematic and chiral nematic liquid crystalline solvents

Cited by 25 publications

References 7 publications

Molecular Interactions in Chiral Nematic Liquid Crystals and Enantiotopic Discrimination through the NMR Spectra of Prochiral Molecules I: Rigid Solutes

Molecular Interactions in Chiral Nematic Liquid Crystals and Enantiotopic Discrimination through the NMR Spectra of Prochiral Molecules I: Rigid Solutes

NMR Spectroscopy Investigation of the Cooperative Nature of the Internal Rotational Motions in Acetophenone

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

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