C_Ar-H⋯O hydrogen bonds in substituted isobenzofuranone derivatives: Geometric, topological, and nmr characterization

Substituted isobenzofuranone derivatives 1a-3a and bindone 4 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 1a-3a (independent of substituent nature) and in 4 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 1a-3a and 5.6 kcal/mol for 4. Both in crystals and in solutions, hydrogen bond strength increases in the order 1a < 2a < 3a 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 1a-3a and 1b-3b (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 ¹J(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).