The 1H NMR data for the two anomers included very comparable peaks in the d 2.0-5.6 region but differed in that, as their highest δ peaks, anomer V had a doublet at d 5.8 (1H, J = 12 Hz) while anomer VI had a doublet at d 6.3 (1H, J = 4 Hz).
(a) Which proton in these anomers would be expected to have these highest δ values?
(b) Why do the signals for these protons appear as doublets?
(c) The relationship between the magnitude of the observed coupling constant and the dihedral angle (when measured using a Newman projection) between C--H bonds on the adjacent carbons of a C--C bond is given by the Karplus equation. It indicates that an axial-axial relationship results in a coupling constant of about 9 Hz (observed range is 8-14 Hz) and an equatorial-axial relationship results in a coupling constant of about 2 Hz (observed range is 1-7 Hz). Which of V and VI is the a anomer and which is the β anomer?
(d) Draw the most stable conformer for each of V and VI.