Which of the following pairs of compounds could be separated by recrystallization or distillation?
a. meso-tartaric acid and (±)-tartaric acid (HOOC—CHOH—CHOH—COOH)

Verified step by step guidance

1. Step 1: Understand the physical properties of the compounds in question. Meso-tartaric acid and (±)-tartaric acid are stereoisomers. Meso-tartaric acid is achiral due to internal symmetry, while (±)-tartaric acid is a racemic mixture of two enantiomers.
2. Step 2: Consider recrystallization as a separation method. Recrystallization relies on differences in solubility. Meso-tartaric acid and (±)-tartaric acid may have different solubility profiles in a given solvent, allowing for separation through selective crystallization.
3. Step 3: Evaluate distillation as a separation method. Distillation separates compounds based on differences in boiling points. Since both compounds are solid at room temperature and have similar functional groups, distillation is unlikely to be effective for their separation.
4. Step 4: Focus on recrystallization. To separate these compounds, dissolve the mixture in a solvent where one compound is more soluble than the other at a given temperature. Upon cooling, the less soluble compound will crystallize out first.
5. Step 5: Confirm the separation method. Analyze the crystallized product using techniques like melting point determination or spectroscopy to ensure successful separation of meso-tartaric acid and (±)-tartaric acid.

Key Concepts

Recrystallization

Recrystallization is a purification technique used to separate compounds based on their solubility differences. In this process, a solid compound is dissolved in a hot solvent and then allowed to cool, leading to the formation of pure crystals. The impurities remain in the solution, allowing for the isolation of the desired compound. This method is particularly effective for compounds with different solubility profiles.

Distillation

Distillation is a separation technique that exploits differences in boiling points of compounds. In this process, a mixture is heated to vaporize the more volatile component, which is then condensed back into a liquid. This method is commonly used for separating liquids or volatile substances, making it useful for purifying solvents or separating liquid mixtures with distinct boiling points.

Stereoisomers

Stereoisomers are compounds that have the same molecular formula and connectivity of atoms but differ in the spatial arrangement of their atoms. Meso compounds, like meso-tartaric acid, possess an internal plane of symmetry, making them achiral, while their enantiomers, such as (±)-tartaric acid, are chiral and exist as non-superimposable mirror images. Understanding the differences in chirality is crucial for determining the separation methods applicable to these compounds.