91Ó°ÊÓ

Two of the four \(\mathrm{D}\) aldopentoses yield \(\mathrm{D}\) -threose on Wohl degradation. What are their structures?

Show how \(N\) -acetylneuraminic acid can arise by an aldol reaction of \(N\) -acetylmannosamine with pyruvate, \(\mathrm{CH}_{3} \mathrm{COCO}_{2}^{-}\).

Write open-chain structures for the following (a) A ketotetrose (b) A ketopentose (c) A deoxyaldohexose (d) A five-carbon amino sugar

Draw Fischer projections of the following molecules: (a) The \(S\) enantiomer of 2 -bromobutane (b) The \(R\) enantiomer of alanine, \(\mathrm{CH}_{3} \mathrm{CH}\left(\mathrm{NH}_{2}\right) \mathrm{CO}_{2} \mathrm{H}\) (c) The \(R\) enantiomer of 2 -hydroxypropanoic acid (d) The \(S\) enantiomer of 3 -methylhexane

Draw Fischer projections for the two \(\mathrm{D}\) aldoheptoses whose stereochemistry at \(\mathrm{C} 3, \mathrm{C} 4, \mathrm{C} 5,\) and \(\mathrm{C} 6\) is the same as that of \(\mathrm{D}\) -glucose at \(\mathrm{C} 2, \mathrm{C} 3, \mathrm{C} 4,\) and \(\mathrm{C} 5\).

Draw D-ribulose in its five-membered cyclic \(\beta\) -hemiacetal form.

Draw structures for the products you would expect to obtain from reaction of \(\beta\) -D-talopyranose with each of the following reagents: (a) \(\mathrm{NaBH}_{4}\) in \(\mathrm{H}_{2} \mathrm{O}\) (b) Warm dilute \(\mathrm{HNO}_{3}\) (c) \(\mathrm{Br}_{2}, \mathrm{H}_{2} \mathrm{O}\) (d) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}, \mathrm{HCl}\) (e) \(\mathrm{CH}_{3} \mathrm{I}, \mathrm{Ag}_{2} \mathrm{O}\) (f) \(\left(\mathrm{CH}_{3} \mathrm{CO}\right)_{2} \mathrm{O}\), pyridine

All aldoses exhibit mutarotation. For example, \(\alpha\) -D-galactopyranose has \([\alpha]_{\mathrm{D}}=+150.7,\) and \(\beta\) -D-galactopyranose has \([\alpha]_{\mathrm{D}}=+52.8 .\) If either anomer is dissolved in water and allowed to reach equilibrium, the specific rotation of the solution is \(+80.2 .\) What are the percentages of each anomer at equilibrium? Draw the pyranose forms of both anomers.

What other \(\mathrm{D}\) aldohexose gives the same alditol as \(\mathrm{D}\) -talose?

Which of the other three \(\mathrm{D}\) aldopentoses gives the same aldaric acid as D-lyxose?