Analysis of the H-bridge in Carboxyllic Acids in Terms of Stabilization Energy Derived from Bond Lengths. Non-Hammett Properties of p-Substituted Benzoic Acids in the Crystalline State

Harmonic oscillator stabilization energy (HOSE) is defined as the negative value of deformation energy necessary to transform a molecule from its natural geometry to its Kekule structure with purely single and double bonds. It was found that HOSE-values for dimers of carboxylic acids with centrosymmetric hydrogen bonds are well related (correlation coeff. r = 0.972) to the Ro . . . o distances for 19 species for which measurements were carried out in both the crystalline and gaseous states. Stability of many other Jt- systems, e. g. aromatic and unsaturated hydrocarbons, polymethine systems (e.g. cyanine dyes), EDA-complexes, quinoid systems, etc. are successfully described in terms of HOSE-values

Infrared and Raman Studies of Carbonyl Group Frequencies of p-Substituted Benzoic Acids in the Crystalline State

Infrared and Raman carbonyl stretching frequencies for p - substituted benzoic acids in the crystalline state were measured and discussed in terms of the Hammett equation and hydrogen · bond strength

Effect of the Orientational Disorder on the Observed Geometry of Carboxylic Group in Dimers of Carboxylic Acids in Crystalline State

Joint considerations of twofold symmetry axes producing various orientations of carboxylic groups and of non-coplanarity of these groups in a dimer lead to a new classification of orientational disorder in crystal s of cyclic dimers of carboxylic acids. Analysis of the geometry and particularly of the anisotropic thermal parameters of carboxylic atoms allows one to distinguish between the possible types of orientational disorder. Influences of dynamic disorder and mesomeric effects are discussed as well

Metal Complexation and H-bonding Effects on Electronic Structure of Cytosine Studied in the Gas Phase

The influence of H-bonding and complexation with cations (probed by HF, F–, Li+, Na+ and K+) on structural and π-electron changes in the six most stable cytosine tautomers has been studied in the gas phase using the B3LYP/6-311++G(2d,2p) computational level. The presence of two exo- groups (ami-no/imino and carbonyl/hydroxyl) in cytosine tautomers significantly increases their sensitivity to structur¬al changes due to intra- and intermolecular interactions. These interactions induce large changes in aroma¬ticity of the rings and in the CX (X = N, O) bond lengths of exocyclic groups. Three types of H-bonds, considering their strength, could be distinguished: (i) charge-assisted X–•••HF, X = N or O, as the strong¬est, (ii) neutral X•••HF, where X is the nitrogen atom of the ring or imino group or the keto form oxygen atom and (iii) also neutral X•••HF, where X being either amino N or alternatively hydroxylic O. Hydrogen bond energy decreases approximately twice in the above listed sequence of interactions. Structural conse¬quences of H-bonding and metal complexation have been observed not only in the immediate region of the interaction but also in other parts of the molecule (the shape of the amino group, changes in CO and CN bond lengths). Complexation of the cytosine tautomers with cations leads to monotonic changes in aromaticity in line with an increase of their ionic radii

Infrared and Raman Studies of Carbonyl Group Frequencies of p-Substituted Benzoic Acids in the Crystalline State

Infrared and Raman carbonyl stretching frequencies for p - substituted benzoic acids in the crystalline state were measured and discussed in terms of the Hammett equation and hydrogen · bond strength

Why 1,2‑quinone derivatives are more stable than their 2,3‑analogues?

In this work, we have studied the relative stability of 1,2- and 2,3-quinones. While 1,2-quinones have a closed-shell singlet ground state, the ground state for the studied 2,3-isomers is open-shell singlet, except for 2,3-naphthaquinone that has a closed-shell singlet ground state. In all cases, 1,2-quinones are more stable than their 2,3-counterparts. We analyzed the reasons for the higher stability of the 1,2-isomers through energy decomposition analysis in the framework of Kohn–Sham molecular orbital theory. The results showed that we have to trace the origin of 1,2-quinones’ enhanced stability to the more efficient bonding in the π-electron system due to more favorable overlap between the SOMOπ of the ·C4n−2H2n–CH·· and ··CH–CO–CO· fragments in the 1,2-arrangement. Furthermore, whereas 1,2-quinones present a constant trend with their elongation for all analyzed properties (geometric, energetic, and electronic), 2,3-quinone derivatives present a substantial breaking in monotonicity.European Union in the framework of European Social Fund through the Warsaw University of Technology Development Programme. O.A. S., H. S. and T.M. K

Substituent Constants (σp−) of the Rotated Nitro Group. The Interplay Between the Substituent Effect of a Rotated −NO2 Group and H-Bonds Affecting π-Electron Delocalization in 4-Nitrophenol and 4-Nitrophenolate Complexes: a B3LYP/6-311+G** Study

The geometries of a series of nine 4-substituted nitrophenols and 4-substituted nitrophenolates (X = H, CONH2, CHO, COOH, COCH3, COCl, CN, NO2, NO) and of their conformers, where the nitro group rotates by 10º from φ = 0° to φ = 90°, were optimized at the B3LYP/6-311+G** DFT level. These data were used to analyse the effect of rotating of the nitro group on π-electron delocalization in the ring. It has been shown that the substituent effect stabilization energy (SESE) estimated for p-substituted phenolates correlates very well with σp− constants. Based on this dependence the σp− constants for the nitro group as a function of the out-of-plane dihedral angle φ were obtained. Application of the model simulating varying strength of H-bond by approaching F− (HF) group to OH (O−) group of the 4-nitrophenol (4-nitrophenolate) with the rotating nitro group allowed to show interrelation between changes in aromaticity of the ring due to both rotation of the nitro group and changes in the strength of H-bonding. Two indices of aromaticity: Nucleus-Independent Chemical Shifts (NICS), and the Harmonic Oscillator Model of Aromaticity (HOMA) were used to quantify the aromatic character of the benzene fragment

The electron density of delocalized bonds (EDDB) applied for quantifying aromaticity

In this study the recently developed electron density of delocalized bonds (EDDB) is used to define a new measure of aromaticity in molecular rings. The relationships between bond-length alternation, electron delocalization and diatropicity of the induced ring current are investigated for a test set of representative molecular rings by means of correlation and principal component analyses involving the most popular aromaticity descriptors based on structural, electronic, and magnetic criteria. Additionally, a qualitative comparison is made between EDDB and the magnetically induced ring-current density maps from the ipsocentric approach for a series of linear acenes. Special emphasis is given to the comparative study of the description of cyclic delocalization of electrons in a wide range of organic aromatics in terms of the kekulean multicenter index KMCI and the newly proposed EDDBk indexThe research was supported in part by the Faculty of Chemistry at Jagiellonian University (grant K/DSC/001469, DS), Foundation for Polish Science (FNP START 2015, stipend 103.2015, DS), National Science Centre, Poland (NCN SONATA, grant 2015/17/ D/ST4/00558, DS) as well as the PL-Grid Infrastructure of the Academic Computer Centre CYFRONET with the calculations performed on the cluster platform ‘‘Prometheus’’. MS thanks for the support of the Ministerio de Economa y Competitividad of Spain (Project CTQ2014-54306-P), Generalitat de Catalunya (project number 2014SGR931, Xarxa de Refere`ncia en Qumica Teo`rica i Computacional, and ICREA Academia prize), and European Fund for Regional Development (FEDER grant UNGI10-4E-801