Proton and 13C NMR spectra of substituted methyl cyanopropionates: Effects of molecular asymmetry

The proton NMR spectra at 220 MHz of two series of substituted cyanopropionates, have been investigated. In addition the 13C spectra at 15 MHz of the series I were also studied. In I, where the R groups are diastereotopic, differences are observed in the proton chemical shifts of the CH3 groups in R for R = CH3, C2H5, n-C3H7, i-C3H7, n-C4H9, n-C5H11 and n-C6H13. In II [R′ = n-C3H7, CH(CH3)2, CH2CH(CH3)2 and C(CH3)3] diastereoisomers are found with substantial differences in chemical shifts between corresponding protons. Coupling constants are interpreted in terms of conformational preferences for certain molecules in both series.