21127-91-3Relevant articles and documents
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Newman,Deno
, p. 3644,3645 (1951)
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Conformational studies by dynamic NMR.78.1 Stereonmutation of the helical enantiomers of trigonal carbon diaryl-substituted compounds: Dimesitylketone, dimesitylthioketone, and dimesitylethylene
Grilli,Lunazzi,Mazzanti,Casarini,Femoni
, p. 488 - 495 (2007/10/03)
The free energies of activation for the enantiomerization of the title compounds (Mes2C=X, Mes = 2,4,6,-trimethylphenyl) were determined by dynamic NMR to be 4.6, 6.5, and 9.2 kcal mol-1 for X= O, S, and CH2, respectively. Single-crystal X-ray diffraction showed that the structure of dimesitylketone is that of a propeller (C2 symmetry) with the mesityl rings twisted by 50° with respect to the plane of carbonyl. The same structure was predicted by molecular mechanics calculations, which also produced good agreement between computed and experimental barriers for a dynamic process where a disrotatory one-ring flip pathway reverses the helicity of the conformational enantiomers. Solid-state NMR spectra indicated that the enantiomerization barrier in the crystal must be much higher (at least 19 kcal mol-1) than that in solution. Contrary to the case of dimesitylketone, the calculated barrier of dimesitylethylene agrees better with the experimental value if the enantiomerization process is assumed to be a conrotatory two-ring flip pathway.
Resolution and Enantiomerization Barrier of Tetramesitylethylene
Gur, Erez,Kaida, Yuriko,Okamoto, Yoshio,Biali, Silvio E.,Rappoport, Zvi
, p. 3689 - 3693 (2007/10/02)
The 1H NMR spectrum of tetramesitylethylene (2) was analyzed, and the signals were assigned by means of a 2D NOESY spectrum.Attempts to observe anisochrony of the enantiotopic groups of a racemic mixture of 2 in a chiral solvent by 1H NMR were unsuccesful.Molecular mechanics and MNDO calculations satisfactorily reproduce the ground-state conformation.The calculated barrier for the enantiomerization process is 21.8 (MM2) and 28.2 (MNDO) kcal mol-1. 2 was chromatographically resolved on a (+)-poly(triphenylmethyl)methacrylate (PTrMA) column.Its specific rotation is 25 = -12100 deg at 365 nm and -2300 deg at 589 nm (D line).The activation parameters for the enantiomerization of 2 in perhydrofluorene are ΔG = ΔH = 39.6 kcal mol-1 and ΔS = 0 cal mol-1 K-1.The barrier for 2 is the highest determined experimentally for a correlated rotation.
