Nuclear magnetic shielding of monoboranes : calculation and assessment of 11B NMR chemical shifts in planar BX3 and in tetrahedral [BX4]- systems
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11B NMR chemical shifts of tricoordinated BX3 and tetracoordinated BX4- compounds (X = H, CH3, F, Cl, Br, I, OH, SH, NH2, and CH=CH2) were computed and the shielding tensors were explored not only within the nonrelativistic GIAO approach but also by applying both relativistic ZORA computations including spin-orbit coupling as well as by employing scalar nonrelativistic ZORA computations (BP86 level of density functional theory). The contributions of the spin-orbit coupling to the overall shieldings are decisive for X = Br and I in both series. No relationship was found between the 2p orbital occupancies or 1/∆E (difference between LUMO and suitably occupied MO that can be coupled with LUMO) with the shielding tensors (or their principal values) in the BX3 series. However, a multidimensional statistical approach known as factor analysis (frequently used in chemometrics) revealed that three factors account for 92 % of the cumulative proportion of total variance. The main components of the first factor are occupancies in the 2px and 2py orbitals and 1/∆E, the second factor is mainly the occupancy in the 2pz orbital and the inductive substituent parameters by Taft and, finally, the third factor consists exclusively (99.3 %) of the electrostatic potentials (Vmax), which is directly related to the so-called π-hole magnitudes.
Machacek , J , Buehl , M , Fanfrlik , J & Hnyk , D 2017 , ' Nuclear magnetic shielding of monoboranes : calculation and assessment of 11 B NMR chemical shifts in planar BX 3 and in tetrahedral [BX 4 ] - systems ' , Journal of Physical Chemistry A , vol. 121 , no. 50 , pp. 9631-9637 . https://doi.org/10.1021/acs.jpca.7b09831
Journal of Physical Chemistry A
© 2017 American Chemical Society. This work has been made available online in accordance with the publisher’s policies. This is the author created accepted version manuscript following peer review and as such may differ slightly from the final published version. The final published version of this work is available at: https://doi.org/10.1021/acs.jpca.7b09831
DescriptionThe financial support of the Czech Science Foundation (project No. 17-08045S) is gratefully acknowledged.
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