Q2. What is the effect of the equatron on the vicinal coupling?
By studying the conformational changes due to different substituents in a series of closely related compounds, most of the uncertainties in the constants in the Karplus equation and in the other factors (e.g. bond lengths, bond angles), influencing the vicinal coupling constants, are largely eliminated.
Q3. What is the effect of the ring oxygen on the doublets of the anomeric?
As a consequence of the strong deshiekling effect of the ring oxygen, the doublets of the anomeric protons (H-l) are found between 6 = 4-3 and 5-7 ppm.
Q4. What is the vicinal coupling constant for the three rotamers?
An indication, that the parallel 1,3-interaction is a very important factor in disfavouring a rotamer, is given by the negligible amounts of rotamer 3 in the o-galactopyranose units of 5, 6, 9 and IO (n3 - 0, columns a and b).
Q5. What are the mole fractions of the l-thiopentakis-OA?
For the compound l-thiopentakis-OAc-/3-D-galactopyranose the following mole fractions were found n, = O-09, nz = 0.91 and rz3 = 003, in which n, and n2 can be interchanged.
Q6. What is the average distortion of the ring fragments?
Although the axial group at C-l has only the ring oxygen at the adjacent place, it is still likely that the overall effect is a less pronounced flattening of this ring fragment (Fig 5) and a decreasing of 4.
Q7. What is the tbis value of the chi-osi?
J”H’= (7~8-l~cos#~+5~6cos2~)(1-O~lAX) (2)*A value of 3.5 for )(oTLbs was used; tbis value was calculated by the method of Cavanaugb and Dailey” from PMR data of CHs-CHI-OSi(CH$s.16
Q8. What is the spectral structure of the glucopyranose unit?
In the glucopyranose unit the protons H-3, H-4, H-5 and H-6 give rise to a complex multiple& which could not be analyzed further.
Q9. What is the likely reason why the TMS-D-galactopyranose?
This result reinforces the conclusions about the TMS-D-galactopyranoses, because it is likely to assume that the TMS- andAC-derivatives of D-galactopymnose do not differ greatly with respect to the conformational preferences of the C-5-C-6 fragment.
Q10. what is the effect of a tronegative group on vicinal coupling?
An elecpresent when 0 = 0” (Fig 3b); if 0 = 60” the effect is tronegative group R has its maximum effect when R nearly absenP (Fig 3~).