Nuclear magnetic shielding of monoboranes : calculation and assessment of 11B NMR chemical shifts in planar BX3 and in tetrahedral [BX4]- systems

The financial support of the Czech Science Foundation (project No. 17-08045S) is gratefully acknowledged.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.PostprintPeer reviewe

STRUCTURAL CHANGES AS A FUNCTION OF TORSIONAL MOTION

Author Institution: Department of Chemistry, Moscow State University; Department of Chemistry, Oslo College of Engineering.; Department of Chemistry., The University of TexasStructural changes as a function of the torsional angle about the central A-A bond have been studied for $X^{3}A-AX_{3}$ molecules with $A = C, Si, Ge$ and $X = H, F, Cl$ and for $X_{2}A=AX_{2}$ molecules with $A = N, P$ and $X = H, F, Cl$ by ab initio calculations. Double or triple zeta basis sets with added polarization functions have been used. The results are compared with experimental values where the latter are available. Simple empirical formulas are presented for simulation of the structure changes and the implications are discussed for analysis of experimental structural determinations by spectroscopy or electron diffraction

Géométrie et structure électronique (méthode CNDO/2) du triala-1,3,5-tris(diméthyl)triaza-2,4,6-cyclohexahetrane [(CH

La validité relative des deux géométries récemment proposées, l’une (A) par spectrographie de rayons X et l’autre (B) par diffraction électronique, pour la molécule [(CH3)2NAlH2]3 est testée au moyen de la méthode CNDO/2. On montre ainsi que l’énergie totale obtenue avec la seconde est quelque 122 kcal/mole inférieure à celle à laquelle conduit la première. Il apparaît lors du calcul une interaction transannulaire [math] liante qui stabilise la conformation privilégiée et dont l’importance numérique (sensiblement moitié de l’énergie EN.Al associée à l’une des liaisons du cycle) souligne la nécessité d’utiliser une description topologique pour décrire la structure électronique de cycles renfermant plus d’un atome de la 3e ligne du tableau périodique