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Chapter 28: Problem 18

The following terms are all related to optical isomers. Explain the meaning of each: (a) diastereomers; (b) enantiomers; (c) \((-) ;\) (d) D configuration.

Short Answer

Expert verified
Diastereomers are non-mirror image stereoisomers of a compound, and they can have different physical properties. Enantiomers are mirror-image isomers, have the same physical properties but can differ in biological activity. A \(-\) sign indicates that a compound is levorotatory, meaning it rotates plane-polarized light to the left. The D-configuration refers to a compound that rotates plane-polarized light to the right.

Step by step solution

01

Definition of Diastereomers

Diastereomers are a type of stereoisomer. They refer to non-mirror image stereoisomers of a compound. That is, diastereomers are stereoisomers that are not enantiomers. Different diastereomers of a compound can have different physical properties, like melting point, boiling point, and solubility.
02

Definition of Enantiomers

Enantiomers also fall under the category of stereoisomers. Specifically, they are mirror-image isomers of a compound. These pairs of isomers are non-superimposable, meaning they cannot be perfectly aligned even if rotated. They have the same physical properties, but they can interact differently with plane-polarized light and often have different biological activity.
03

Meaning of \(-\)

A \(-\) sign in a compound's name denotes that it is a 'levorotatory' compound. This means that the compound is able to rotate plane-polarized light to the left when it is passed through a solution of the compound.
04

Definition of D-configuration

The D-configuration (or 'Dextrorotatory configuration') of a compound indicates that it rotates plane-polarized light to the right. This is not the same as being an R-configuration compound, as the R and S system is based on the absolute configuration of the molecule, while the D and L system is based on the compound's optical activity.

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Most popular questions from this chapter

The pure \(\alpha\) and \(\beta\) forms of \(\mathrm{D}\) -glucose rotate the plane of polarized light to the right by \(112^{\circ}\) and \(18.7^{\circ},\) respectively (denoted as +112 and +18.7 ). Are these two forms of glucose enantiomers or diastereomers?

The amino acid ( \(R\) )-alanine is found in insect larvae. Draw the Fischer projection of this amino acid.

The term "epimer" is used to describe diastereomers that differ in the configuration about a single carbon atom. Which pairs of the eight possible aldopentoses are epimers?

Describe what is meant by each of the following terms, using specific examples where appropriate: (a) polypeptide; (b) protein; (c) N-terminal amino acid; (d) \(\alpha\) helix; (e) denaturation.

Refer to a typical Escherichia coli bacterium. This is a cylindrical cell about \(2 \mu\) m long and \(1 \mu\)m in diameter, weighing about \(2 \times 10^{-12}\)g and containing about \(80 \%\) water by volume. Calculate the number of lipid molecules present, assuming their average molecular mass to be 700 u and the lipid content to be \(2 \%\) by mass.
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