Which of the following molecules cannot undergo an intramole

Which of the following molecules cannot undergo an intramolecular aldol condensation when treated with NaOH? IV

Solution

Option 5 is the right answer. Compound 1 to compound 4 forms 5 membered 5 on undergoing intramolecular aldol condensation. But compound 5 will form 4 membered ring which is unstable. Hence compound 5 donot show intramolecular aldol condensation.