Question

Complete reaction of acetaldehyde with excess formaldehyde, upon heating with conc. NaOH solution, gives P and Q. Compound P does not give Tollens' test, whereas Q on acidification gives positive Tollens' test. Treatment of P with excess cyclohexanone in the presence of catalytic amount of p-toluenesulfonic acid (PTSA) gives product R.
Sum of the number of methylene groups (-CH2-) and oxygen atoms in R is _______

Answer 1

Correct Answer: 18

Step 1: Identifying P and Q 

The reaction of acetaldehyde with formaldehyde under aldol condensation conditions (conc. NaOH, heat) leads to the formation of:

• P: 2,2,4,4-Tetramethyl-1,3-dioxane (does not give Tollens’ test, indicating the absence of an aldehyde group).
• Q: Formic acid precursor (on acidification gives a positive Tollens’ test, confirming its identity).

Step 2: Formation of R

P undergoes an acid-catalyzed reaction with excess cyclohexanone, forming a spirocyclic ketone derivative.

Step 3: Counting the Methylene (-CH-) Groups and Oxygen Atoms

• The spirocyclic product R consists of 16 methylene (-CH-) groups.
• It contains 2 oxygen atoms from the ketone and ether functionalities.
• Total sum = 16 + 2 = 18.