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Intrinsic information content of NMR dipolar couplings: a conformational investigation of 1,3-butadiene in a nematic phase

Intrinsic information content of NMR dipolar couplings: a conformational investigation of 1,3-butadiene in a nematic phase
Intrinsic information content of NMR dipolar couplings: a conformational investigation of 1,3-butadiene in a nematic phase

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 DCH dipolar couplings is determined from the analysis of the 1H spectra of the three 1,3-butadiene most-abundant isotopomers (i.e. the all 12C and the two single-labeled 13C isotopomers) for a total of 21 independent dipolar couplings. A very good starting set of spectral parameters for the analysis of the 1H 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.

C satellite spectra, Conformation analysis, Liquid crystals, NMR spectroscopy, Vibrational corrections
1439-4235
1930-1943
Celebre, Giorgio
bffb0a16-65d1-44a2-93b4-c6f65d59d834
Concistré, Maria
8574cc9a-726e-49b7-b136-fe6bb043b424
De Luca, Giuseppina
8152f554-4aa6-42bf-af23-c0d74db9f69e
Longeri, Marcello
3b1f11d6-2c93-4221-898b-b85385f0b0ed
Pileio, Giuseppe
13f78e66-0707-4438-b9c9-6dbd3eb7d4e8
Celebre, Giorgio
bffb0a16-65d1-44a2-93b4-c6f65d59d834
Concistré, Maria
8574cc9a-726e-49b7-b136-fe6bb043b424
De Luca, Giuseppina
8152f554-4aa6-42bf-af23-c0d74db9f69e
Longeri, Marcello
3b1f11d6-2c93-4221-898b-b85385f0b0ed
Pileio, Giuseppe
13f78e66-0707-4438-b9c9-6dbd3eb7d4e8

Celebre, Giorgio, Concistré, Maria, De Luca, Giuseppina, Longeri, Marcello and Pileio, Giuseppe (2006) Intrinsic information content of NMR dipolar couplings: a conformational investigation of 1,3-butadiene in a nematic phase. ChemPhysChem, 7 (9), 1930-1943. (doi:10.1002/cphc.200600220).

Record type: Article

Abstract

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 DCH dipolar couplings is determined from the analysis of the 1H spectra of the three 1,3-butadiene most-abundant isotopomers (i.e. the all 12C and the two single-labeled 13C isotopomers) for a total of 21 independent dipolar couplings. A very good starting set of spectral parameters for the analysis of the 1H 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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More information

Published date: 11 September 2006
Keywords: C satellite spectra, Conformation analysis, Liquid crystals, NMR spectroscopy, Vibrational corrections

Identifiers

Local EPrints ID: 414790
URI: https://eprints.soton.ac.uk/id/eprint/414790
ISSN: 1439-4235
PURE UUID: 3eb7c350-206a-4a2a-9594-3b91ec8f7cb6
ORCID for Giuseppe Pileio: ORCID iD orcid.org/0000-0001-9223-3896

Catalogue record

Date deposited: 11 Oct 2017 16:31
Last modified: 14 Mar 2019 01:42

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