Question

The optically active tartaric acid is named as \(\mathrm{D}-(+)\) tartaric acid because it has a positive (a) Optical rotation and is derived from D-glucose (b) \(\mathrm{pH}\) in an organic solvent (c) Optical rotation and is derived from D-(+)glyceraldehyde (d) Optical rotation only when substituted by deuterium

Short answer

The correct answer is (c): Optical rotation and derived from D-(+)glyceraldehyde.

Step-by-step solution

Understanding Optical Activity

Optical activity refers to the ability of a chiral substance to rotate the plane of polarization of a beam of light that passes through it. Substances that rotate light clockwise (to the right, or dextrorotatory) are labeled as "+". This aligns with option (c), where D-(+) indicates positive optical rotation.

Exploring Derivation from Reference Compounds

The label 'D' in carbohydrate chemistry refers to the configuration of the chiral center farthest from the carbonyl group and is based on its relation to D-(+)-glyceraldehyde. This means the configuration of hydroxyl groups in D-(+)-tartaric acid is similar to that in D-(+)-glyceraldehyde, thus supporting option (c).

Analyzing Other Options

Option (a) states that D-(+)-tartaric acid is derived from D-glucose, which describes a common pathway for sugars but doesn't directly relate to derivation definition from a reference compound like glyceraldehyde. Option (b), mentioning pH, and option (d), involving substitution by deuterium, are unrelated to optical rotation and stereochemistry. Thus, they can be excluded.

Key concepts

Tartaric Acid

Tartaric acid is a naturally occurring organic acid that is most commonly associated with grapes and is a crucial component in winemaking. This acid is responsible for the tart taste in many wines and is used in a variety of food industries due to its ability to regulate acidity.

Among its unique properties, tartaric acid is known for its ability to exist in different stereoisomeric forms. These forms include

• D-(+)-tartaric acid
• L-(-)-tartaric acid
• meso-tartaric acid
• racemic mixture (DL-tartaric acid)

These isomeric forms have important practical ramifications, particularly in the field of stereochemistry, affecting both physical properties and biological functions. The optically active isomers, such as D-(+)-tartaric acid, possess chiral characteristics that allow them to rotate plane-polarized light.

Chiral Substances

Chirality is a geometric property of some molecules and ions. A chiral molecule is one that is not superimposable on its mirror image. Such molecules typically have at least one carbon atom bonded to four different atoms or groups, creating a chiral center.

Chiral substances are crucial in chemistry because they can influence biological activity significantly. For instance, enantiomers (non-superimposable mirror images) of a chiral compound may differ drastically in their effects on the human body.

• An example is the medication Thalidomide, where one enantiomer has therapeutic effects, while the other caused birth defects.
• Chirality also explains why D-(+)-tartaric acid, with a specific chiral configuration, exhibits optical activity.

Chiral substances and their rotations (either to the right or left) are foundational concepts in both organic chemistry and biochemistry.

Dextrorotatory Compounds

Dextrorotatory compounds are those that can rotate plane-polarized light to the right, or clockwise. This optical activity is measured using a polarimeter and is a characteristic property of substances that possess chirality.

To denote dextrorotatory compounds in chemical notation, the prefix '(+)' is used. This is to indicate the direction of light rotation, not to confuse with the '(-)' prefix which indicates rotation to the left or levorotatory orientation.
For students learning about optical activity:

• Remember that the specific rotation is an intrinsic property of the compound's molecular structure.
• D-(+)-tartaric acid is dextrorotatory, implying it has a positive specific optical rotation.

Identifying whether a compound is levorotatory or dextrorotatory is an important part of understanding stereochemistry.

Derivation from D-(+)-glyceraldehyde

The chiral nature of tartaric acid is determined by its derivation from simpler molecules like D-(+)-glyceraldehyde. This molecule is used as a standard reference point in stereochemistry for determining the configuration of chiral centers in sugars.

Carbohydrates, including tartaric acid, have their chiral centers defined using a comparison to D-(+)-glyceraldehyde, which possesses one chiral center itself. In this reference system:

• If the configuration around a designated chiral center matches that of D-(+)-glyceraldehyde, the compound is given the label 'D'.
• This is important not just for nomenclature but for predicting the biological activity and synthesis of related compounds.

This derivation system underscores how molecular chirality is crucial for understanding both chemical reactivity and metabolic pathways.