Question

Product of D-aldotetroses with conc. \(HNO_3\) gives optically inactive dicarboxylic acid. Which among the following will be D-Aldotetrose in the given structures? 

• A. Structure (1)
• B. Structure (2)
• C. Structure (3)
• D. Structure (4)

Answer 1

The Correct Option is A

Concept: Oxidation of aldoses with concentrated nitric acid converts both the aldehyde group \((-CHO)\) and the terminal alcohol group \((-CH_2OH)\) into carboxylic acids. \[ CHO \xrightarrow{HNO_3} COOH \] \[ CH_2OH \xrightarrow{HNO_3} COOH \] Thus an aldose forms a dicarboxylic acid. If the product is optically inactive, it must be a meso compound.
Step 1: Structure of D-aldotetrose Aldotetrose contains: \[ CHO-(CHOH)_2-CH_2OH \] After oxidation: \[ COOH-(CHOH)_2-COOH \]
Step 2: Condition for optical inactivity The resulting dicarboxylic acid will be optically inactive only if it possesses a plane of symmetry (meso form). This occurs when the two middle chiral centers have identical substituent orientation.
Step 3: Check structures In structure (1), the two \(OH\) groups are arranged symmetrically. After oxidation the product becomes: \[ COOH-CH(OH)-CH(OH)-COOH \] This molecule has an internal plane of symmetry, hence it is optically inactive.
Step 4: Conclusion Thus the correct D-aldotetrose is: \[ \boxed{\text{Structure (1)}} \]