(a) Heating d-altrose with dilute acid produces a nonreducing anhydro sugar (C6H10O5). Methylation of the anhydro sugar followed by acid hydrolysis yields 2, 3, 4-tri-O-methyl- D-altrose. The formation of the anhydro sugar takes place through a chair conformation of β-D-altropyranose in which the --CH2OH group is axial. What is the structure of the anhydro sugar, and how is it formed?
(b) D-Glucose also forms an anhydro sugar but the conditions required are much more drastic than for the corresponding reaction of D-altrose. Explain.