Carboalkoxy group, 131 Table

The lesser stereoselectivity observed for the acrylate dimers [2c] in THF is readily understood in terms of the lesser coordinative ability of the carboalkoxy group compared to that of pyridine ( 7) (Table 3). 

The reverse anomeric effect was postulated for the carboalkoxy group (29,37,42) in an O—C—COOR system, but it was proved (38) (see also Table 4) that in fact one deals here with a normal anomeric effect. Recent calculations by Altona s group (72) on the conformation of molecules of the type X—CH2—OCH3 (X = COOH, COO , C N, C=CH) revealed that the changes in bond lengths on going from the ap to the sc conformation... 

The variation of vf values shown in Table II indicates that 2 prefers different microenvironments within a family of polymers. In PMMA, PMA and PVAc matrices, 2 is basically located in the vicinity of the polymer backbone (the polar carboalkoxy group). This is confirmed by the low vf values (20325-20408 cm-1) observed in these three polymers, which have an effective dielectric constant of 20. The 4>f of 2 in PMMA, PMA and PVAc are 0.0123, 0.013 and 0.011, respectively, despite their large differences in Tg values. The similar < if values in these three polymers suggests that the polymer chain flexibility (or free volume) around the polymer backbones of PRMA, PRA and probably poly(vinyl alkanoate) is probably very similar. 

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