Problem 73 - A Complete Resource Book in Chemistry for JEE Main

Question

The compound (1) and (2) can be regarded as CC(C)C(O)C(C)O CC(O)C(C)O (1) (2) (a) enantiomers (b) diastereomers (c) mesomers (d) geometrical isomer

Step-by-Step Solution

Answer

The compounds (1) and (2) are diastereomers.

Step 1: Understand the Definitions

Enantiomers are non-superimposable mirror images; diastereomers are non-mirror image stereoisomers that are not enantiomers; mesomers (or resonance structures) have different arrangements of electron pairs but are the same molecule; geometrical isomers have different spatial arrangements around a double bond or ring.

Step 2: Analyze the Molecular Structures

The molecular structure given in SMILES of (1) is CC(C)C(O)C(C)O and of (2) is CC(O)C(C)O. Both represent different arrangements of carbon and hydroxyl groups, indicating stereochemistry needs consideration.

Step 3: Evaluate Chiral Centers

For compound (1), identify chiral centers, noting CC(C)C(O) group has a chiral center at the carbon bonded to the OH. Compound (2) has a simpler structure with hydroxyls on adjacent carbon atoms, which also may indicate chiral centers.

Step 4: Determine Stereoisomeric Relationship

Compound (1) may not simply mirror compound (2) given differences in substituent arrangements. Analyze if they are arranged in fixed spatial direction (diastereomers) or if they can be considered mirror images (enantiomers).

Step 5: Conclude Based on Stereochemistry

Since compound (1) cannot be superimposed on compound (2) and possess different spatial arrangements of groups around chiral centers without being mirror images, they are diastereomers.

Key Concepts

Chirality

Chirality is an essential concept in stereochemistry and refers to the property of a molecule having a non-superimposable mirror image, much like how our left and right hands are mirror images but not identical. This concept is significant because molecules with chiral centers often exhibit different behaviors in biological and chemical contexts. A molecule with chirality has at least one carbon atom with four different substituents attached, making it a chiral center, also known as a stereocenter. This results in two possible configurations for each chiral center, usually designated as "R" and "S" configurations based on specific priority rules.

• Chiral molecules lack a plane of symmetry.
• They usually involve carbon atoms bonded to four different groups.
• Such molecules often interact differently with other chiral environments, such as enzymes or receptor sites.

Enantiomers

Enantiomers are a type of stereoisomer that are mirror images of each other but cannot be superimposed. This means that even though they have the same molecular and structural formula, they are different in terms of spatial arrangement. Each chiral molecule has a pair of enantiomers with opposite configurations at all chiral centers. The presence of enantiomers is crucial in the pharmaceutical industry because each enantiomer can have very different effects in biological systems. Identification of enantiomers typically involves techniques like polarimetry, which measures the direction and degree to which each enantiomer can rotate plane-polarized light.

• Enantiomers share identical physical properties, such as melting points and boiling points, in non-chiral environments.
• They differ in their optical activity, with one enantiomer rotating plane-polarized light clockwise (dextrorotary) and the other counterclockwise (levorotary).

Diastereomers

Diastereomers are stereoisomers that are not related as mirror images; they differ in configuration at one or more chiral centers. Unlike enantiomers, diastereomers have different physical properties, such as melting points, boiling points, and solubilities, which make them easier to separate in a laboratory setting.

• They have different chemical reactivity and physical properties.
• They can differ at one or more, but not all, chiral centers in molecules with multiple chiral centers.

Diastereomers include a subclass known as epimers, where there is a difference in configuration at only one chiral center between two compounds. Separation techniques for diastereomers include crystalization and various forms of chromatography. Recognizing diastereomers is essential in stereochemistry to understand molecule behavior beyond simple mirror image scenarios.

Geometrical Isomers

Geometrical isomers, also known as cis-trans isomers, are a type of stereoisomerism arising from restricted rotation around a bond, usually a double bond or a cyclic structure. These isomers do not involve chiral centers but instead differ in the spatial arrangement of substituents.

• Cis isomers have substituents located on the same side of the double bond or ring, whereas trans isomers have substituents on opposite sides.
• They exhibit different physical and chemical properties, like polarity and boiling points, due to different spatial orientations.
• Applications include the design of materials and pharmaceuticals that exploit the unique aspects of these arrangements for specific functions.

Geometrical isomerism plays a prominent role in the chemistry of alkenes and complex compounds, where the spatial arrangement of atoms profoundly influences properties and reactivity.