Aromatic C−H^...O Interactions in a Series of Bindone Analogues. NMR and Quantum Mechanical Study

Abstract

The aromatic C-H...O hydrogen bonding within the series of the structurally relative indenone derivatives has been studied. The presence of the hydrogen bonds is corroborated by the large low-field chemical shifts of the protons involved in the hydrogen bond observed experimentally and reproduced by quantum mechanical calculations. Further confirmation is provided by analysis of the orbital overlap coefficients, (13)C NMR chemical shifts, and one-bond spin-spin coupling constants J((13)C-(1)H). The relationship between molecular geometry and (1)H NMR chemical shifts of involved protons has a complex nature, but the C-H...O distance is the principal factor.

Direct Evidence for Methyl Group Coordination by Carbon-Oxygen Hydrogen Bonds in the Lysine Methyltransferase SET7/9

“…1) (23, 66 -69); thus, we sought to verify our experimental chemical shift change using quantum chemistry calculations. Although this combination of techniques has been used to identify CH⅐⅐⅐O hydrogen bonds in small organic molecules (37,70,71) and in computational biology (68), it has, to our knowledge, not yet been applied experimentally in biological macromolecules. Using this combination of techniques, we reasoned that it should be possible to solve for the hydrogen positions and, thus hydrogen bonding patterns, of the AdoMet methyl group within the SET7/9 active site.…”

“…Previous studies of CH⅐⅐⅐O hydrogen bonding in small organic molecules showed that the chemical shift calculations of hydrogen were usually accurate to 0.1 ppm of the experiment (37,70,71). Error in biological molecules could arise from many sources, including but not limited to implicit solvation modeling and large or truncated molecules used in calculations.…”

Inter‐ and Intramolecular C–H···O Bonding in the Anions of 1,3‐Indandione Derivatives

“…[18] However, the hydrogens at the sp 2 carbon atoms in anions 2a and 3a meet the above-mentioned criteria [20] and are hydrogen bonded. This is supported by an increase in the respective one-bond coupling constants 1 J( 13 C, 1 H) from 164.1 Hz for C-2 in 1a to 172.7 Hz for C-11 in 2a, and to 177.5 Hz for C-11 in 3a ( Table 1).…”

“…Recently, we demonstrated [18] that the geometry of the C-H···O=C fragments of derivatives 2-4 meet the criteria, which set the limits for possible C-H···O hydrogen bonding occurrence. [20] A detailed NMR spectroscopic and quantum mechanical study revealed the following manifestations of hydrogen bonding: (1) large low-field chemical shifts of the protons and carbon atoms involved, (2) increase in the onebond ( 13 C, 1 H) spin-spin coupling constants, and (3) non-zero positive values of the overlap coefficients between the orbitals involving the interacting oxygen and hydrogen atoms.…”

“…Recently, we demonstrated [18] that the molecular geometry of derivatives 2-4 allows formation of intramolecular hydrogen bonds between the aromatic C-H atoms and oxygen atom of one of the carbonyl groups. At the same time, when the 1 H and 13 C NMR spectra of these derivatives were studied in polar solvents, we observed a number of irregularities (e.g., signal broadening), which can stem from partial ionization of the neutral species.…”