
Concept explainers
(a)
Interpretation: The number of stereogenic centers present in
Concept introduction: Carbohydrates are naturally occurring compounds. Carbohydrates are polyhydroxy

Answer to Problem 21.39P
There are five stereogenic centers present in
Explanation of Solution
The stereogenic centers in
Figure 1
The stereogenic centers are marked by star. There are five stereogenic centers present in
There are five stereogenic centers present in
(b)
Interpretation: The hemiacetal carbon in
Concept introduction: Carbohydrates are naturally occurring compounds. Carbohydrates are polyhydroxy aldehydes and ketones. Galactose is a aldohexose as it contains six carbon atoms as well as an aldehyde functional group. The molecular formula of galactose
Aldehydes or ketones on reaction with one equivalent of alcohol form hemiacetal and on reaction with two equivalents of alcohol it forms acetals. This is nucleophilic addition reaction. These reactions takes place in presence of acids, commonly
Ethers contain only one alkoxy group on a carbon atom while acetals contain two alkoxy groups on a single carbon atom.
Hemiacetals contains one alkoxy group and one hydroxyl group attached to same carbon atom.

Answer to Problem 21.39P
The hemiacetal carbon in
Explanation of Solution
The hemiacetal carbon in
Figure 2
The highlighted carbon contains alkoxy group and hydroxyl group. Hence, this carbon is labeled as hemiacetal carbon.
The hemiacetal carbon in
(c)
Interpretation: The structure of
Concept introduction: Carbohydrates are naturally occurring compounds. Carbohydrates are polyhydroxy aldehydes and ketones. Galactose is a aldohexose as it contains six carbon atoms as well as an aldehyde functional group. The molecular formula of galactose

Answer to Problem 21.39P
The structure of
Explanation of Solution
In
Figure 3
The structure of
(d)
Interpretation: The structure of poly hydroxy aldehyde that cyclizes to
Concept introduction: Carbohydrates are naturally occurring compounds. Carbohydrates are polyhydroxy aldehydes and ketones. Galactose is a aldohexose as it contains six carbon atoms as well as an aldehyde functional group. The molecular formula of galactose
Aldehydes or ketones on reaction with one equivalent of alcohol form hemiacetal and on reaction with two equivalents of alcohol it forms acetals. This is nucleophilic addition reaction. These reactions takes place in presence of acids, commonly
In

Answer to Problem 21.39P
The structure of poly hydroxy aldehyde that cyclizes to
Explanation of Solution
The cyclization of poly hydroxy aldehyde results in the formation of hemiacetal. The hydroxyl group on
Figure 4
The structure of poly hydroxy aldehyde that cyclizes to
(e)
Interpretation: The products formed when
Concept introduction: Carbohydrates are naturally occurring compounds. Carbohydrates are polyhydroxy aldehydes and ketones. Galactose is a aldohexose as it contains six carbon atoms as well as an aldehyde functional group. The molecular formula of galactose
Aldehydes or ketones on reaction with one equivalent of alcohol form hemiacetal and on reaction with two equivalents of alcohol it forms acetals. This is nucleophilic addition reaction. These reactions takes place in presence of acids, commonly

Answer to Problem 21.39P
The products formed when
Explanation of Solution
Cyclic hemiacetals can be converted to acetals by treatment with alcohol in presence of acid. The hydroxyl group of hemiacetal is converted to alkoxy group. The
Figure 5
The products formed when
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Chapter 21 Solutions
ORGANIC CHEMISTRY
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