C_Ar–H···O Hydrogen Bonds in Substituted Isobenzofuranone Derivatives: Geometric, Topological, and NMR Characterization

Abstract

Substituted isobenzofuranone derivatives <b>1a</b>–<b>3a</b> and bindone <b>4</b> are characterized by the presence of an intramolecular C_Ar–H···O hydrogen bond in the crystal (X-ray), solution (¹H NMR and specific and nonspecific IEF-PCM solvation model combined with MP2 and B3LYP methods), and gas (MP2 and B3LYP) phases. According to geometric and AIM criteria, the C_Ar–H···O interaction weakens in <b>1a</b>–<b>3a</b> (independent of substituent nature) and in <b>4</b> with the change in media in the following order: gas phase > CHCl₃ solution > DMSO solution > crystal. The maximum value of hydrogen bond energy is 4.6 kcal/mol for <b>1a</b>–<b>3a</b> and 5.6 kcal/mol for <b>4</b>. Both in crystals and in solutions, hydrogen bond strength increases in the order <b>1a</b> < <b>2a</b> < <b>3a</b> with the rising electronegativity of the ring substituents (H < OMe < Cl). The best method for calculating ¹H NMR chemical shifts (δ^calcd – δ^expl < 0.7 ppm) of hydrogen bonded and nonbonded protons in <b>1a</b>–<b>3a</b> and <b>1b</b>–<b>3b</b> (isomers without hydrogen bonds) is the GIAO method at the B3LYP level with the 6-31G** and 6-311G** basis sets. For the C–H moiety involved in the hydrogen bond, the increase of the spin–spin coupling constant ¹<i>J</i>(¹³C–¹H) by about 7.5 Hz is in good agreement with calculations for C–H bond shortening and for blue shifts of C–H stretching vibrations (by 55–75 cm^–1)