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Intra‐ and Intermolecular C(sp 2 )–H···O Hydrogen Bonds in a Series of Isobenzofuranone Derivatives: Manifestation and Energetics
Author(s) -
Niebel Claude,
Lokshin Vladimir,
Sigalov Mark,
Krief Pnina,
Khodorkovsky Vladimir
Publication year - 2008
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200800357
Subject(s) - intramolecular force , chemistry , hydrogen bond , intermolecular force , chloroform , hydrogen atom , chemical shift , computational chemistry , hydrogen , solvent , molecule , binding energy , crystallography , stereochemistry , group (periodic table) , organic chemistry , physics , nuclear physics
Derivatives 2 – 6 were prepared as models for studying intra‐ and intermolecular C(sp 2 )–H ··· O hydrogen bonding. Their X‐ray structures confirm the presence of intramolecular hydrogen bonds in derivatives of the “ a ” series: the corresponding C ··· O distances vary between 2.91 and 2.97 Å. The corresponding 13 C– 1 H coupling constants are increased by about 7.5 Hz, and the 1 H chemical shifts in CDCl 3 are 9.1–10.7 ppm. No intramolecular hydrogen bonds can form in derivatives of the isomeric “ b ” series. In this series, the chemical shifts of the corresponding aromatic protons exhibit strong solvent dependency; in particular, they are as sensitive as the proton in chloroform to the presence of DMSO. The vinylic protons activated by the electron‐accepting COOR groups behave similarly. Quantum mechanical calculations in the gas phase and in DMSO reproduce the experimental observations. Energies of the intramolecular hydrogen bonds evaluated by two independent approaches vary between 3.7 and 4.4 kcal mol –1 in the gas phase and still amount to at least 2.5 kcal mol –1 in 2a in DMSO. These estimates are practically independent of the computational method (HF, MP2, and DFT B3LYP were employed for derivatives 2 ). We conclude that the behavior of both activated aromatic and vinylic C(sp 2 )–H atoms in the studied derivatives is qualitatively and quantitatively similar to the behavior of the C(sp 3 )–H atom in chloroform. The existence of hydrogen bonds involving these atoms can easily be detected by NMR spectroscopy.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)