Aromaticity of benzenoid hydrocarbons with inserted –B=B– and –BH–BH– groups : a comparison

Structures of selected polycyclic conjugated hydrocarbons with -B=B- and -BH-BH- moieties inserted in different places were calculated at the B3LYP/6-311++Glevel and their aromatic properties evaluated. HOMA, NICS(0), NICS(1)zz, Λ and PDI indices were used for studying their aromatic properties. Both optimized planar (as in parent hydrocarbons) and non-planar structures were taken into account. It is shown that insertion of both types of boron groups disturbs and decreases the aromaticity of the corresponding hydrocarbons. The decreasing effect of the -BH-BH- group is much stronger. What is quite intriguing is that it appears that non-planar structures of the studied compounds have a little higher aromaticity than the strictly planar ones. Mutual correlations between results obtained by different aromaticity indices are calculated and thoroughly discussed.We thank the Ministerio de Ciencia e Innovación (Project No. CTQ2012-35513-C02-02) and the Comunidad Autónoma de Madrid (Project MADRISOLAR2, ref. S2009/PPQ-1533) for their continuing support. Thanks are also given to “ICM” Warsaw (Project Number G17-8) and to the CTI (CSIC) computer centers for an allocation of computer time.Peer Reviewe

Activation of dinitrogen as a dipolarophile in 1,3-Dipolar Cycloadditions: A theoretical study using nitrile imines as “Octet” 1,3-Dipoles

Theoretical calculations at the G4MP2 level of theory demonstrate that it is possible to activate dinitrogen to make it react in dipolar cycloadditions using neutral beryllium derivatives and other neutral metallic compounds. For the particular case of beryllium, the barrier decreases more than 40 kJ·mol -1 with respect to the non-catalysed reaction. The activation achieved is lower than using diazonium salts (models of protonated N 2 ), but still in a range that can be experimentally attainableThis work was carried out with financial support from the Ministerio de Economía y Competitividad (Project No. CTQ2015-63997-C2-2-P) and Comunidad Autónoma de Madrid (Project FOTOCARBON, ref. S2013/MIT-2841). Computer, storage and other resources from the CTI (CSIC) are gratefully acknowledged. M. M. Montero-Campillo also thanks Project FOTOCARBON for her research contrac

Nucleophilicities of Lewis Bases B and Electrophilicities of Lewis Acids A Determined from the Dissociation Energies of Complexes B⋯A Involving Hydrogen Bonds, Tetrel Bonds, Pnictogen Bonds, Chalcogen Bonds and Halogen Bonds

It is shown that the dissociation energy D e for the process B⋯A = B + A for 250 complexes B⋯A composed of 11 Lewis bases B (N2, CO, HC≡CH, CH2=CH2, C3H6, PH3, H2S, HCN, H2O, H2CO and NH3) and 23 Lewis acids (HF, HCl, HBr, HC≡CH, HCN, H2O, F2, Cl2, Br2, ClF, BrCl, H3SiF, H3GeF, F2CO, CO2, N2O, NO2F, PH2F, AsH2F, SO2, SeO2, SF2, and SeF2) can be represented to good approximation by means of the equation D e = c ′ N B E A , in which N B is a numerical nucleophilicity assigned to B, E A is a numerical electrophilicity assigned to A, and c ′ is a constant, conveniently chosen to have the value 1.00 kJ mol−1 here. The 250 complexes were chosen to cover a wide range of non-covalent interaction types, namely: (1) the hydrogen bond; (2) the halogen bond; (3) the tetrel bond; (4) the pnictogen bond; and (5) the chalcogen bond. Since there is no evidence that one group of non-covalent interaction was fitted any better than the others, it appears the equation is equally valid for all the interactions considered and that the values of N B and E A so determined define properties of the individual molecules. The values of N B and E A can be used to predict the dissociation energies of a wide range of binary complexes B⋯A with reasonable accuracy

Unusual Complexes of P(CH)3 with FH, ClH, and ClF

© 2020 by the authors.Ab initio MP2/aug’-cc-pVTZ calculations have been performed to determine the structures and binding energies of complexes formed by phosphatetrahedrane, P(CH)3, and HF, HCl, and ClF. Four types of complexes exist on the potential energy surfaces. Isomers A form at the P atom near the end of a P-C bond, B at a C-C bond, C at the centroid of the C-C-C ring along the C3 symmetry axis, and D at the P atom along the C3 symmetry axis. Complexes A and B are stabilized by hydrogen bonds when FH and ClH are the acids, and by halogen bonds when ClF is the acid. In isomers C, the dipole moments of the two monomers are favorably aligned but in D the alignment is unfavorable. For each of the monomers, the binding energies of the complexes decrease in the order A > B > C > D. The most stabilizing Symmetry Adapted Perturbation Theory (SAPT) binding energy component for the A and B isomers is the electrostatic interaction, while the dispersion interaction is the most stabilizing term for C and D. The barriers to converting one isomer to another are significantly higher for the A isomers compared to B. Equation of motion coupled cluster singles and doubles (EOM-CCSD) intermolecular coupling constants J(X-C) are small for both B and C isomers. J(X-P) values are larger and positive in the A isomers, negative in the B isomers, and have their largest positive values in the D isomers. Intramolecular coupling constants 1J(P-C) experience little change upon complex formation, except in the halogen-bonded complex FCl:P(CH3) AThis work was carried out with financial support from the Ministerio de Ciencia, Innovación y Universidades of Spain (Project No. PGC2018–094644-B-C22) and Comunidad Autónoma de Madrid (P2018/EMT–4329 AIRTEC-CM)

A theoretical and experimental NMR study of the prototropic tautomerism of tris(tetrabutylammonium) hydrogen pyrophosphate salt in solution and in the solid-state

The structure of tris(tetrabutylammonium)hydrogen pyrophosphate(HPP) has been studied in solution and in the solid-state by 31P NMR. GIAO/DFT calculations of the isolated molecule in its open and closed conformations, of their water complexes and the solvent effects (continuum model) have been useful to discuss the experimental NMR data. Contrary to literature reports, the 31P NMR spectra of HPP in solution have a single band, that broadenedconsiderably when the temperature is lowered till 193 K without reaching the coalescence. In the solid-state, two very close signals are observed that the calculations do not reproduce adequately

Systematic behaviour of electron redistribution on formation of halogen-bonded complexes B⋯XY, as determined via XY halogen nuclear quadrupole coupling constants

Equilibrium nuclear quadrupole coupling constants associated with the di-halogen molecule XY in each of 60 complexes B⋯XY (where B is one of the Lewis bases N, CO, HCN, HO, HS, HCCH, CH, PH, NH or (CH)N and XY is one of the di-halogens Cl, BrCl, Br, ICl, IBr or I) have been calculated ab initio. The Townes-Dailey model for interpreting the changes in the coupling constants when XY enters the complex was used to describe the electron redistribution in the di-halogen molecule in terms of the fraction δ of an electron transferred from the Lewis base B to atom X and the fraction δ of an electron transferred simultaneously from atom X to atom Y. Systematic relationships between the δ values for the six series are established. It is shown that, in reasonable approximation, δ decays exponentially as the first ionisation energy I of the Lewis base B increases, that is δ = Aexp(-bI). It is concluded from the results for the series B⋯BrCl, B⋯Br, B⋯ICl, B⋯IBr and B⋯I that the coefficients A and b in regression fits to the corresponding logarithmic version ln(δ) = ln(A) - b(I) of the equation are not strongly dependent on either the halogen atom X directly involved in the halogen bond in B⋯XY or, for a given X, on the nature of Y. The behaviour of PH as a Lewis base appears to be anomalous. Values of δ and δ calculated by the quantum theory of atoms-in-molecules and natural bond orbital methodologies are very close to those from application of the Townes-Dailey approach described.IA thanks Ministerio de Ciencia, Innovación y Universidades (Project No. PGC2018-094644-B-C22) and Comunidad Auto´noma de Madrid (P2018/EMT-4329 AIRTEC-CM) for financial support. ACL thanks the University of Bristol for the award of a Senior Research FellowshipPeer Reviewe

Barriers about Double Carbon-Nitrogen Bond in Imine Derivatives (Aldimines, Oximes, Hydrazones, Azines)

The paper presents the results referring to the inversion mechanism of imines and their derivatives (hydrazones, oximes, azines). The calculated barriers [B3LYP/6-311++G(d,p) and G3B3)] are in good agreement with the scarce existing data. The transition states correspond in all cases to a pure nitrogen inversion except in the case of azines where they have some rotation character. The electron properties of the minima and the transition states have been characterized, allowing explanation of the geometrical changes observed in the process

The Structure of N-Benzylazoles from Pyrrole to Carbazole: Geometries and Energies

International audienceThe complete series of 18 parents N-benzylazoles (10 azoles and 8 benzazoles) have been calculated at the B3LYP/6-311++G(d,p) level. The geometries have been compared with the X-ray structures reported in the literature for six derivatives (1H-imidazole, 1H-1,2,3-triazole, 1H-1,2,3,4-tetrazole, 1H-benzimidazole, 1H-benzotriazole, and 9H-carbazole). Only one minimum has been found for the 18 molecules, but several transition states connecting them have been located. The calculated geometries agree well with those reported by X-ray crystallography

Cations brought together by hydrogen bonds: The protonated pyridine-boronic acid dimer explained

According to the Cambridge Structural Database, protonated pyridine-boronic acid dimers exist in the solid phase, apparently defying repulsive coulombic forces. In order to understand why these cation-cation systems are stable, we carried out M06-2X/6-311++G(3df,2pd) electronic structure calculations and used a set of computational tools (energy partitioning, topology of the electron density and electric field maps). The behavior of the charged dimers was compared with the corresponding neutral systems, and the effect of counterions (Br - and BF 4- ) and the solvent (PCM model) on the binding energies has been considered. In the gas-phase, the charged dimers present positive binding energies but are local minima, with a barrier (16-19 kJ mol -1 ) preventing dissociation. Once the environment is included via solvent effects or counterions, the binding energies become negative; remarkably, the strength of the interaction is very similar in both neutral and charged systems when a polar solvent is considered. Essentially, all methods used evidence that the intermolecular region where the HBs take place is very similar for both neutral and charged dimers. The energy partitioning explains that repulsion and electrostatic terms are compensated by the desolvation and exchange terms in polar solvents, thus giving stability to the charged dimerThis work was carried out with financial support from the Ministerio de Economía, Industria y Competitividad (Projects No. CTQ2015-63997-C2-2-P, CTQ2014-57393-C2-1-P and CTQ2017-85821-R FEDER funds) and Comunidad Autónoma de Madrid (S2013/MIT2841, Fotocarbon