33509-38-5Relevant academic research and scientific papers
17O and 13C NMR Spectra of Stable Simple Enols
Frey, Joseph,Eventova, Irina,Rappoport, Zvi,Mueller, Thomas,Takai, Yoshio,Sawada, Masami
, p. 621 - 638 (2007/10/02)
17O NMR spectra of twelve stable simple enols 1 t, m- and p-substituted aryl, mesityl> were measured in CDCl3 and od six of them in DMSO. 13C spectra of all the enols were measured in both solvents.These are the first values measured for enols not strongly intramolecularly hydrogen bonded.The δ(17O) values in CDCl3 are divided into three groups which parallel the steric bulk of R: (i) 70.5-74.9 when R = H; (ii) 84.1-87.4 when R = m- and p-substituted aryl; (iii) 93.0-98.5 ppm for R = But, mesityl (Mes). ΔδO = δ(17O) DMSO> - δ(17O) = 7-10 for group (i), ca. 3 for group (ii) and -17 for trimesitylethenol 1l.IGLO calculations on CH2=CHOH (4) give a shallow parabola for the δ(17O) vs. the C=C-O-H torsional angle θ plot, with maxima at θ = 0 and 180 deg (syn and anti planar conformations) and a minimum at θ = 90 deg. δ(13C-2) values show an approximate mirror-image change while δ(13C-1) changes slightly with θ.Calculation on the solvates 4*O=SH2 with syn, anti and perpendicular conformations show trends similar to those for uncomplexed 4 with upfield shifts of δ(17O, 13C-2) and downfield shift of δ(13C-1, 1H) in all conformations.When the calculations also included the effect of the reaction field, the δ(17O) values of the perpendicular and anti conformations differ little from those of uncomplexed 4.PM3 calculations for four enols including 1c and 1l also show a minimum at θ = 90 deg and the plot of ΔfH for 1c and 1l vs. θ resemble the calculated energy (by MP2/6-311G**) vs. θ plot for 4.No correlation exists between the Ar-C=C torsion angles or λmax of the enols with δ(17O), but the polar effect of the α-substituent affects the δ(17O) values.The solvent effect is ascribed to OH-DMSO hydrogen bonding, accompanied by a conformational change from syn-periplanar in CDCl3 to mainly anti-clinal in DMSO.A lower association with DMSO for bulkier Rs and an accompanying change of θ towards 90 deg qualitatively account for the ΔδO values.Several correlations between the δ(17O), δ(1H) and δ(13C) shifts or of δ(13C) and Hammett's ? values were found.
