28. Carbohydrates

Determine the structure of the alditol formed when b-D-xylofuranose is treated with NaBH4 and then water. Explain how NaBH4 can reduce the hemiacetal group of the furanose. 

Identify the sugar in each description.

a. An aldopentose that is not d-arabinose forms d-arabinitol when it is reduced with NaBH4.

Identify the sugar in each description.

c. A ketose that, when reduced with NaBH4, forms d-altritol and d-allitol.

b. What monosaccharide is reduced to two alditols, one of which is the alditol obtained from the reduction of

1. d-talose? 

2. d-allose?

When D-glucose is reduced with sodium borohydride, optically active glucitol results. When optically active D-galactose is reduced, however, the product is optically inactive. Explain this loss of optical activity.