Which of the following compounds is classified as an acetal?

• A. A molecule with two hydroxyl groups ($\mathrm{OH}$) attached to the same carbon atom
• B. A molecule with a carbonyl group ($C=O$) bonded to two alkyl groups
• C. A molecule with two ${\mathrm{OR}}_1$ and ${\mathrm{OR}}_2$ groups attached to the same carbon atom
• D. A molecule with a hydroxyl group ($\mathrm{OH}$) and an ether group ($\mathrm{OR}$) attached to the same carbon

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the definition of an acetal. An acetal is a functional group where a single carbon atom is bonded to two alkoxy groups (\( OR_1 \) and \( OR_2 \)) and typically also bonded to two other substituents, often hydrogens or alkyl groups. This carbon is usually derived from the reaction of an aldehyde or ketone with alcohols under acidic conditions.
2. Step 2: Analyze the options given. The first option describes a carbon with two hydroxyl groups (\( OH \)) attached, which corresponds to a geminal diol, not an acetal.
3. Step 3: The second option describes a carbonyl group (\( C=O \)) bonded to two alkyl groups, which defines a ketone, not an acetal.
4. Step 4: The third option describes a carbon atom bonded to two alkoxy groups (\( OR_1 \) and \( OR_2 \)), which matches the definition of an acetal.
5. Step 5: The fourth option describes a carbon with one hydroxyl group (\( OH \)) and one ether group (\( OR \)), which is a hemiacetal, an intermediate between aldehydes/ketones and acetals.