Enumerating structural isomers of esters with formula C4H8O2

Steps:

• Esters follow RCOOR' formula; total carbons in R + R' +1 (carbonyl) =4.
• Formate esters (R=H, R'=C3H7): n-propyl formate (HCOOCH2CH2CH3) and isopropyl formate (HCOOCH(CH3)2).
• Acetate esters (R=CH3, R'=C2H5): ethyl acetate (CH3COOCH2CH3).
• Propanoate esters (R=C2H5, R'=CH3): methyl propanoate (CH3CH2COOCH3).
• No other combinations yield C4H8O2 for saturated carboxylate esters.

Why C is correct:

• Exactly four structural isomers exist, as confirmed by partitioning the carbon chain across acid and alcohol moieties.

Why the others are wrong:

• A. 2: Underestimates by ignoring chain and branching variants.
• B. 3: Misses isopropyl formate isomer.
• D. 5: Overcounts; no additional saturated ester fits the formula.

Final answer: C