The effect of benzoannulation on the transition state and the proton transfer equilibrium in di(2-pyridyl)methane derivatives

Abstract

The tautomeric properties of di(2-pyridyl)methane and its benzoannulated derivatives were studied using a computational approach (M05/6-31G(2d,p)). Our analysis showed that the degree of cyclic p-electron delocalization in benzene and pyridine rings is directly connected to the effect of resonance present in quasi-rings formed by intramolecular hydrogen bonds of the N-HÁ Á ÁN type. This direct relation can be explained using two concepts, namely, the concept of Clar's aromatic sextet and the Leffler-Hammond concept originally developed for the explanation of the energy relation between ground-state and transition-state structures corresponding to proton transfer in H-bridges. Application of these two different concepts allows us to explain in detail the role of intramolecular hydrogen bonding in polycyclic aromatic hydrocarbons containing N heteroatoms. w Electronic supplementary information (ESI) available: Cartesian coordinates, computed total energies of optimized structures, aromaticity indices, densities of total electron energy at the ring critical points, and definitions of aromaticity indices. See

Association ofN-(Pyridin-2-yl),N′-substituted Ureas with 2-Amino-1,8-naphthyridines and Benzoates: NMR and Quantum Chemical Studies of the Substituent Effect on Complexation

“…Interactions such as XH···O (X = N, O, C), − FH···F, CH···F and NH···F, NH···O and OH···O, and FH···N have been used to test and develop this methodology. We have successfully used this approach to describe and explain the properties of intramolecular NH···N and intermolecular , hydrogen bonding.…”

“…92,93 Originally Espinosa used the properties of H-BCP (hydrogen bond critical point) for various hydrogen bond bridges except the 92 and FH•••N 97 have been used to test and develop this methodology. We have successfully used this approach to describe and explain the properties of intramolecular NH•••N 98 and intermolecular 37,48 hydrogen bonding.…”

The influence of CH bond polarization on the self-association of 2-acylaminopyrimidines by NH/CH···O/N interactions: XRD, NMR, DFT, and AIM study

“…Moreover, the same approach has been used to study the hydrogen bond bridges in which the hydrogen bond acceptor carries three (FHÁÁÁFF [58], NHÁÁÁF, CHÁÁÁF [59]), two (NHÁÁÁO, or OHÁÁÁO [54]), and one lone electron pair (FHÁÁÁNH 3 [59]). This method have also been used in explaining the properties of intramolecular hydrogen bonds (NHÁÁÁN [60]) and intermolecular ones that stabilize dimer, trimers and tune the properties of rotamers in supramolecular assemblies [16,61]. It is fair to mention that we used this approach to highlight the differences in energy of interactions between NHÁÁÁN/O and CHÁÁÁN/O contacts, while the QTAIM was shown to be applicable for many structures where the hydrogen bonding is described as purely non-covalent interaction (even a weak one [62]) or it is considered as partially covalent one with relatively high bond orders [63].…”

Photophysical Properties of Phenacylphenantridine Difluoroboranyls: Effect of Substituent and Double Benzannulation

“…The fusion of benzo ring(s) with the central core of a conjugated molecule can greatly impact its properties, as demonstrated by several studies on various compounds, including polyacenes. − In addition, benzannulation may change the energy of the transition state in proton transfer reaction, tune the position of the proton (enol carrying OH group or enamine carrying NH group) in a series of tautomerizable CH-acids, ,, as well as the photophysical properties of organic compounds. For instance both blue- and red-shifts of the absorption spectra have been observed depending on the position of the benzannulation .…”