Weak C–H···O and Dipole–Dipole Interactions as Driving Forces in Crystals of Fluorosubstituted Phenylboronic Catechol Esters

The analysis of weak interactions in crystals of a series of fluorosubstituted phenylboronic catechol esters (fphb) supported by Hirshfeld surface analysis is presented. The influence of the number and positions of fluorine atoms on the molecular structure is discussed and compared with results of the DFT calculations for isolated molecules. The molecular symmetry breaking caused by the intermolecular interactions was detected. The substantial differentiation of the dipole moments generated by fluorine substitution and its consequence on molecular packing are analyzed. The presence of <i>ortho</i>-fluoro substituents was found to enhance the proton acceptor character of oxygen atoms. Consequently, the C–H···O hydrogen-bonded centrosymmetric dimer is the dominating motif for molecules with small dipole moments. Otherwise, the antiparallel dipole–dipole interactions are responsible for the supramolecular architecture

Dependence of the Substituent Effect on Solvent Properties

The influence of a solvent on the substituent effect (SE) in 1,4-disubstituted derivatives of benzene (BEN), cyclohexa-1,3-diene (CHD), and bicyclo[2.2.2]­octane (BCO) is studied by the use of polarizable continuum model method. In all X–R–Y systems for the functional group Y (NO₂, COOH, OH, and NH₂), the following substituents X have been chosen: NO₂, CHO, H, OH, and NH₂. The substituent effect is characterized by the charge of the substituent active region (cSAR­(X)), substituent effect stabilization energy (SESE), and substituent constants σ or <i>F</i> descriptors, the functional groups by cSAR­(Y), whereas π-electron delocalization of transmitting moieties (BEN and CHD) is characterized by a geometry-based index, harmonic oscillator model of aromaticity. All computations were carried out by means of B3LYP/6-311++G­(d,p) method. An application of quantum chemistry SE models (cSAR and SESE) allows to compare the SE in water solutions and in the gas phase. Results of performed analyses indicate an enhancement of the SE by water. The obtained Hammett-type relationships document different nature of interactions between Y and X in aromatic and olefinic systems (a coexistence of resonance and inductive effects) than in saturated ones (only the inductive effect). An increase of electric permittivity clearly enhances communications between X and Y for BEN and CHD systems