Measuring multiple 17O–13C J-couplings in naphthalaldehydic acid: a combined solid state NMR and density functional theory approach

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Rees, G.J., Day, S.P., Barnsley, K.E., Iuga, D., Yates, J.R., Wallis, J.D. ORCID: 0000-0001-7259-8783 and Hanna, J.V., 2020. Measuring multiple 17O–13C J-couplings in naphthalaldehydic acid: a combined solid state NMR and density functional theory approach. Physical Chemistry Chemical Physics, 22 (6), pp. 3400-3413. ISSN 1463-9076

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Official URL: https://doi.org/10.1039/c9cp03977e

Abstract

A combined multinuclear solid state NMR and gauge included projected augmented wave, density functional theory (GIPAW DFT) computational approach is evaluated to determine the four heteronuclear 1J(13C,17O) couplings in solid 17O enriched naphthalaldehydic acid. Direct multi-field 17O magic angle spinning (MAS), triple quantum MAS (3QMAS) and double rotation (DOR) experiments are initially utilised to evaluate the accuracy of the DFT approximations used in the calculation of the isotropic chemical shifts (diso), quadrupole coupling constants (CQ) and asymmetry (ZQ) parameters. These combined approaches give diso values of 313, 200 and 66 ppm for the carbonyl (CQO), ether (–O–) and hydroxyl (–OH) environments, respectively, with the corresponding measured quadrupole products (PQ) being 8.2, 9.0 and 10.6 MHz. The geometry optimised DFT structure derived using the CASTEP code gives firm agreement with the shifts observed for the ether (diso = 223, PQ = 9.4 MHz) and hydroxyl (diso = 62, PQ = 10.5 MHz) environments but the unoptimised experimental XRD structure has better agreement for the carbonyl group (diso = 320, PQ = 8.3 MHz). The determined diso and ZQ values are shown to be consistent with bond lengths closer to 1.222 Å (experimental length) rather than the geometry optimised length of 1.238 Å. The geometry optimised DFT 1J(13C,17O) coupling to the hydroxyl is calculated as 20 Hz and the couplings to the ether were calculated to be 37 (O–CQO) and 32 (O–C–OH) Hz. The scalar coupling parameters for the unoptimised experimental carbonyl group predict a 1J(13C,17O) value of 28 Hz, whilst optimisation gives a value of 27 Hz. These calculated 1J(13C,17O) couplings, together with estimations of the probability of each O environment being isotopically labelled (determined by electrospray ionisation mass spectrometry) and the measured refocussable transverse dephasing (T2 0) behaviour, are combined to simulate the experimental decay behaviour. Good agreement between the measured and calculated decay behaviour is observed.

Item Type:

Journal article

Publication Title:

Physical Chemistry Chemical Physics

Creators:

Rees, G.J., Day, S.P., Barnsley, K.E., Iuga, D., Yates, J.R., Wallis, J.D. and Hanna, J.V.

Publisher:

Royal Society of Chemistry

Date:

14 February 2020

Volume:

Number: