APPLICATION OF F1-DECOUPLED 2D-NMR METHODS FOR CHARACTERIZING THE STEREOCHEMICAL STRUCTURE OF TERT-BUTYL ACRYLATE OLIGOMERS

The stereochemical structure of tert-butyl acrylate (tBuA) oligomers p repared in tetrahydrofuran with tert-butyl-alpha-lithioisobutyrate ini tiation was studied by NMR methods. By combination of various types of one- and two-dimensional NMR methods, resonance lines could be assign ed in H-1 and C-13 NMR spectra of tBuA oligomers (dimer, trimer, tetra mer and pentamer) in C6D6 solution. The unequivocal assignment of NMR resonance lines to various stereoisomers in the tBuA tetramer and pent amer was achieved by means of the f1-decoupled COSY experiment. The tw o isomers present in the sample of tBuA tetramer could be identified a s m (major form) and r (minor form) by means of the f1-decoupled NOESY experiment; their populations amounted to 0.78 and 0.22, respectively . In the sample of tBuA pentamer, the populations of the stereoisomers were mm: mr: rm = 0.635:0.185: 0.180; the population of the rr stereo isomer is negligible (does not exceed 0.05). These stereoisomer popula tions in the tBuA pentamer conform to Bernoullian statistics.