Methyl shift 3-Methylstyrene

Anomalies are also present in the spectrum of poly-a-methylstyrene (Fig. 12 a), in which the oc-methyl resonance is shifted to fields nearly 1.3 p.p.m. higher than that of the methyl groups of the small-molecule... 

Jenner and Kellou recently studied the pressure effect on azeotropy in free-radical terpolymerization of MA with acrylonitrile, dielthyl fumarate, methyl acrylate, methyl methacrylate, methyl vinyl ketone, vinylidene chloride, norbornene, a-methylstyrene, indene, and vinyl acetate, with styrene as the second comonomer common in all cases. It was found that ternary azeotropes were only possible for those systems where the first comonomers had positive e values, i.e., diethyl fumarate, acrylonitrile, methyl acrylate, methyl methacrylate, methyl vinyl ketone, and vinylidene chloride. Surprisingly, the coordinates of the ternary azeotropes were very little affected by variations of the pressure from 1-3,000 bars. Since reactivity ratios in multi-component polymerizations are sensitive to pressure, causing terpolymer composition to also be pressure dependent, a shift of the ternary azeotropic point would be expected. Why this occurs awaits further clarification. 

The stereochemical assignments deserve special comments. The geometries of produds (4) were determined on the basis of the chemical shifts in H-NMR spectra (CDCb) (Figure 1). In a similar manner to /3-methylstyrene (46), (Z)-4a shows the vinylic proton at higher field (4.8 ppm). Likewise, ( )-4b shows the vinylic methyl group at higher field (1.7 ppm). The absolute configuration of (E)-4b was determined to be R by Mosher s method the chemical shift of vinylic methyl proton in H-NMR spectra (CDCb) of MTPA ester of (E)-4b 1.60 ppm (5), 1.36 ppm (R) bs-bR = positive (47),... 

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