β-Diketone interactions. Part 8. The hydrogen bonding of the enol tautomers of some 3-substituted pentane-2,4-diones

Abstract

Three new derivatives of pentane-2,4-dione (PD) have been synthesized: 3-(4-nitrophenyl), 3-(4-phenoxyphenyl) and 3-(4-isopropylphenyl). The X-ray crystal structures of these compounds show them to have very short hydrogen bonds with R(O ⋯ O)= 2.445, 2.443, and 2.419 Å, respectively. Those parameters most sensitive to hydrogen bonding—¹H chemical shift, change in chemical shift on deuteriation [Δδ(H, D)], and stretching frequencies [ν_CO and ν_max.(OHO)]—have been measured for these, and other 3-derivatives of PD, with a view to probing the potential energy well of this type of bond. The conclusion is that in all of the compounds with R(O ⋯ O) < 2.45 Å, the hydrogen bonding is very strong with the proton zero point energy above the internal barrier.