Deck 23: Carbohydrates

Question 1

Which one of the following describes the furanose forms of carbohydrates?

A) a six-membered ring consisting of all carbons
B) a six-membered ring consisting of five carbons and one oxygen
C) a five-membered ring consisting of all carbons
D) a five-membered ring consisting of four carbons and one oxygen

Answer 1

a five-membered ring consisting of four carbons and one oxygen

Question 2

What are the configurations of carbon atoms 2 and 3, respectively, of D-threose, shown below?

A) R,R
B) R,S
C) S,R
D) S,S

Answer 2

S,R

Question 3

The major form of D-glucose in aqueous solution is

A) the open-chain form.
B) $\alpha$ -D-glucopyranose.
C) $\beta$ -D-glucopyranose.
D) $\alpha$ -D-glucofuranose.

Answer 3

$\beta$ -D-glucopyranose.

Question 4

The $\alpha$ and $\beta$ forms of $D$ -glucopyranose can be described as

A) constitutional isomers.
B) enantiomers.
C) different conformations of the same compound.
D) anomers.

Question 5

Identify the $\beta$ -pyranose form of $D$ -glucose.

A)

B)

C)

D)

Question 6

The $\alpha$ - and $\beta$ -pyranose forms of $D$ -glucose interconvert by

A) "ring-flipping" between the two chair conformations.
B) ring-opening and ring-closing through the open-chain aldehyde form.
C) epimerization through the enol tautomer.
D) $\mathrm{S}_{\mathrm{N}} 2$ inversion with nucleophilic hydroxide ion.

Question 7

Which of the following statements is(are) true concerning the equilibrium between the $\alpha$ - and $\beta$ -pyranose forms of D-glucose?
I. The interconversion is acid-catalyzed.
II. Both anomers are equally stable.
III. Both anomers are optically active.

A) only III
B) II and III
C) I and III
D) I, II, and III

Question 8

Identify the anomeric carbon in the following carbohydrate.

A) A
B) B
C) C
D) D

Question 9

The principal difference between amylose (from starch) and cellulose is

A) amylose has exclusively $\alpha(1,4)$ -linked glucose and cellulose has exclusively $\beta(1,4)$ -linked glucose.
B) amylose has exclusively $\alpha(1,6)$ -linked glucose and cellulose has exclusively $\beta(1,4)$ -linked glucose.
C) amylose has $\alpha(1,4)$ -linked glucose with $\alpha(1,6)$ branches and cellulose has exclusively $\beta(1,4)$ -linked glucose.
D) amylose has exclusively $\alpha(1,4)$ -linked glucose and cellulose has $\beta(1,4)$ -linked glucose with $\alpha-(1,6)$ branches.

Question 10

Which of the following give an optically inactive compound when reacted with sodium borohydride, $\mathrm{NaBH}_{4}$ ?

A) I and II
B) II and III
C) III and IV
D) I and IV

Question 11

The following series of reactions was done on a monosaccharide. What information does this give about the monosaccharide?

A) The monosaccharide was in the open-chain form.
B) The monosaccharide was in the furanose form.
C) The monosaccharide was in the pyranose form.
D) The monosaccharide was the $\alpha$ anomer.

Question 12

The $\alpha$ - and $\beta$ -pyranose forms of $D$ -glucose can be described as

A) cyclic acetals formed between the aldehyde and the hydroxy group on carbon-5.
B) cyclic hemiacetals formed between the aldehyde and the hydroxy group on carbon-5.
C) cyclic acetals formed between the aldehyde and the hydroxy group on carbon-6.
D) cyclic hemiacetals formed between the aldehyde and the hydroxy group on carbon-6.

Question 13

Which one of the following is L-(-)-glucose?

A) I
B) II
C) III
D) IV

Question 14

Which statement is not true of the $D$ and $L$ stereoisomers of any given sugar?

A) they have equal but opposite optical rotations
B) they both form cyclic hemiacetals in solution
C) they both undergo the same enzymatic digestion process
D) they can both undergo the $\alpha$ - and $\beta$ -anomer equilibration process

Question 15

What results from the reaction shown?

A)

B)


C)

D)