Question

'All attempts to prepare and study optically active 2 -naphthalenesulfinic acid are doomed to failure." What possible justification could be made for this prediction?

Short answer

The prediction that attempts to prepare and study optically active 2-naphthalenesulfinic acid will fail can be justified based on the molecular structure of the compound. Optical activity is exhibited by chiral molecules, which have an asymmetric carbon atom with four different substituents. Analyzing the structure of 2-naphthalenesulfinic acid, there is no carbon atom with four different substituents. Therefore, it does not possess the necessary molecular structure to exhibit chirality, and consequently, cannot show optical activity.

Step-by-step solution

Understand Optical Activity

Optical activity is a property of chiral molecules. Chiral molecules are not superimposable on their mirror images. To show optical activity, a molecule must have an asymmetric carbon atom, which means that the carbon has four different substituents attached to it.

Analyze 2-naphthalenesulfinic acid structure

The 2-naphthalenesulfinic acid has the molecular formula C10H8SO3. Its chemical structure consists of a naphthalene ring (a fused benzene ring) with a sulfinic acid group (-SO2H) attached to one of its carbon atoms.

Identify the asymmetric carbon atom

To show optical activity, 2-naphthalenesulfinic acid must have at least one asymmetric carbon atom with four different substituents. Inspecting the structure, we can see that there is no carbon atom that has four different substituents. The carbon atoms in the naphthalene ring have two carbon substituents and two hydrogen substituents, and the carbon atom attached to the sulfinic acid group has two carbon substituents, one hydrogen substituent, and the sulfinic acid substituent.

Conclude the prediction

Since there is no asymmetric carbon atom in 2-naphthalenesulfinic acid, it cannot show optical activity. Therefore, all attempts to prepare and study an optically active form of this compound are doomed to failure, as it does not have the necessary molecular structure to exhibit chirality.

Key concepts

Chirality and Asymmetric Carbon Atoms

Chirality is a geometric property of some molecules, indicating that the structure of a molecule cannot be superimposed onto its mirror image. Just like your hands are mirror images but not identical, chiral molecules have this 'handedness'. An asymmetric carbon atom, often called a chiral center, is a carbon atom that is attached to four different atoms or groups of atoms.

Understanding chirality begins with recognizing the central role of the asymmetric carbon. When a carbon atom is bonded to four distinct substituents, it forms two non-superimposable configurations known as enantiomers. These enantiomers are chiral because they differ in spatial arrangement and cannot be superposed, even when rotated. The existence of these enantiomers is essential for optical activity, a property in which a chiral molecule can rotate plane-polarized light.

In the context of an exercise, if a molecule such as 2-naphthalenesulfinic acid is being inspected for chirality, one would look for the presence of an asymmetric carbon. If such a carbon is absent, as in the case of 2-naphthalenesulfinic acid, no amount of effort would result in an optically active compound. This fundamental understanding is crucial as it guides the entire process of analyzing molecules for optical activity.

2-Naphthalenesulfinic Acid Structure

2-Naphthalenesulfinic acid, which has the molecular formula C10H8SO3, is composed of a naphthalene skeleton and a sulfinic acid group attached to it. The naphthalene part of the molecule consists of two fused benzene rings, creating a two-ring system that is planar and aromatic.

Because the molecule's structure forms part of the fundamental knowledge in organic chemistry, understanding it is vital for various analysis, including the assessment of chirality. However, despite its seemingly complex structure replete with carbon and hydrogen atoms, none of the carbons in 2-naphthalenesulfinic acid meet the criterion of an asymmetric carbon atom. This is because none of the carbon atoms carry four different groups. Specifically, the carbon atoms in the naphthalene rings share double bonds and are bound to hydrogens or other carbons, failing to provide the necessary diversity for asymmetry.

Therefore, even if one apprentice might anticipate otherwise based on the molecule's intricate architecture, the lack of an asymmetric carbon atom dooms any attempts to produce an optically active form of 2-naphthalenesulfinic acid.

Properties of Chiral Molecules

Chiral molecules exhibit a set of intriguing and valuable properties. Most notably, they are capable of existing in two forms that are mirror images of each other but not superimposable, similar to a pair of hands. This characteristic is termed enantiomerism. Enantiomers often have identical physical and chemical properties except when interacting with other chiral substances, including biological systems or polarized light.

One of the most remarkable traits of chiral molecules is their ability to demonstrate optical activity. When a beam of plane-polarized light passes through a solution containing a chiral molecule, the plane of polarization is rotated. The direction and magnitude of the rotation depend on the nature of the chiral molecule and its concentration. This property is critical in fields such as pharmaceuticals, where the different enantiomers of a drug can have very different therapeutic effects.

For students cross-examining a molecule like 2-naphthalenesulfinic acid for such properties, recognizing that the absence of a chiral center means that optical activity is not possible, elucidates the key concept: not all molecules with complex structures exhibit chirality, and thus, not all possess the associated properties of chiral molecules.