Intramolecular hydrogen bond directed distribution of conformational populations in the derivatives ofN′-benzylidenebenzohydrazide

Abstract

The extensive NMR investigations reveal the presence of E-isomers in the derivative of N′-benzylidenebenzohydrazide. The different conformer populations are controlled by the strength of intramolecular hydrogen bonds.

Competing HB acceptors: an extensive NMR investigations corroborated by single crystal XRD and DFT calculations

“…However, in many earlier reports, this coupling completely vanished 45,46,48,49 in DMSO except in molecules where the structural restraint resists the complete breaking of HB by DMSO. 26,44 The retention of the 1h J FH for molecule 2 in the DMSO-d 6 is due to the favorable cis geometry (Fig.…”

“…9d), whose value is similar to those observed for other reported molecules. 45,46,[48][49][50][51][52] All these in-depth NMR studies leads to the conclusion that the N-H/X interactions are inuenced by strong pC]O/H HB, which is also reected in the shielding of NH 1 proton and reduced value of 1h J FH in the molecule 2. These narrations suggest that the competitive equilibrium between N-H/X and pC]O/H-N type HBs debilitate with each other and is the possible reason for the shielding of NH 1 proton in the molecules 2 and 3 compared to 1.…”

“…3). 8,44,46 The deshielding in the NH 1 proton chemical shi is inversely proportional to the strength of intramolecular HB in such systems 44,46 because the intramolecular HB minimizes the accessibility of sites for DMSO around the acidic proton. The small change in chemical shis upon DMSO-d 6 addition could possibly be attributed to the favorable near planar geometry of these molecules which also limits the accessibility of the sites for the association of DMSO by creating hindrance.…”

Retention of strong intramolecular hydrogen bonds in high polarity solvents in binaphthalene–benzamide derivatives: extensive NMR studies

“…The energy of HB can be calculated by using experimentally measured chemical shis employing the relation E HB (kcal mol À1 ) ¼ Dd + (0.4 AE 0.2), where Dd pertains to the difference in the chemical shi of proton between the substituted and unsubstituted molecules. 12,33 The calculated E HB for the molecules 1-3 are compiled in Table 1.…”

“…11 The strength of intramolecular HBs also can control the population of different conformers for a molecule. 12 The uorine is one of the essential atoms presents in majority of the drugs due to its bio-availability and stability. On an average nearly 30% of commercial drugs contain at least one uorine atom to enhance the metabolic stability, binding affinity and to alter physicochemical properties.…”