Conformational and electronic interaction studies of some p-substituted α-methylsulfonyl-α-diethoxyphosphorylacetophenones

The analysis of the IR carbonyl band of the α-methylsulfonyl-α-diethoxyphosphoryl p-substituted acetophenones p-Y-Ph-C(O)CH(SO2Me)[P(O)(OEt)2] (Y = OMe 1, H 2, F 3, Cl 4, Br 5 and NO26) supported by HF/6-31G(d,p) ab initio calculations of the α-methylsulfonyl-α-diethoxyphosphoryl acetophenone 2, indicated the existence of a single stable c1 conformer in gas phase and in solvents of increasing polarity, along with the presence of second less stable conformation in gas phase. The c1 conformer present the (SO2Me) group and the [P(O)(OEt2)] groups in a syn-clinal (gauche) geometry and is stabilised through of the Oδ−(CO)...Pδ+(PO), Oδ−[PO(OEt)]...Cδ+(CO), Oδ−(PO)…Cδ+(CO), Oδ−(CO)…Sδ+(SO2Me) and Oδ−(SO2)...Cδ+(CO) electronic interactions along with Hδ+(SO2Me)…. Oδ−(CO), Hδ+(CH2)[POEt]…. Oδ−(SO2Me), Hδ+(o-Ph)…. Oδ−(CO) and Hδ+(o′-Ph)…. Oδ−(PO) intramolecular hydrogen bonds. The almost constant negative carbonyl frequency shifts (Δν) for the title compounds 1-6 with respect to the parent acetophenones 7-14 corroborates the prevalence of the electronic interactions over the −Iσ inductive effect of the α-substituents for the title compounds and gives strong support for the existence of the crossed Oδ−(CO)…Sδ+(SO2Me) and Oδ−(SO2)...Cδ+(CO) (charge transfer and electrostatic); Oδ−(CO)...Pδ+(PO) and Oδ−[PO(OEt)]...Cδ+(CO), (electrostatic) interactions.