PrayogX › Chemistry › Aldehydes, Ketones and Carboxylic Acids

Ozonolysis and intramolecular aldol of bicyclic ring-fusion alkenes: matching four alkenes to their beta-hydroxy ketones

Four bicyclic alkenes whose only C=C is the ring-fusion bond, watched at two levels at once. On the left a flask at −78 °C takes ozone until it turns blue, then zinc dust and water, then aqueous NaOH on a hot plate; on the right every electron pair moves as a curved arrow: 1,3-dipolar cycloaddition, retro-cycloaddition, recombination to the secondary ozonide, two-step zinc reduction to the cyclodecanedione, the more stable enolate and the intramolecular aldol that closes two new rings, then protonation. Q, R and S run through the same eight steps; each product graph is matched with List-II and the options are tested. No prediction stage - input, run, watch, result.

Sub-topics covered

• Ozonolysis - Criegee mechanism (molozonide, carbonyl oxide, secondary ozonide)
• Reductive work-up with Zn / H2O
• Enolate stability and substitution
• Intramolecular aldol reaction and ring size
• Bicyclic ring systems: decalin and hydroazulene

What it teaches

• The ring-fusion C=C is cut: a 6-6 alkene gives cyclodecane-1,6-dione, a 7-5 alkene cyclodecane-1,5-dione
• Zn / H2O reduces the ozonide to two ketones (and ZnO) without further oxidation
• The more stable enolate forms at the CH that bears CH3 (more substituted C=C), provided the ring it closes has at least five atoms
• The enolate attacks the other C=O across the ring: 6-6 alkenes give 5-7 fused beta-hydroxy ketones, 7-5 alkenes give decalins
• P → 2, Q → 1, R → 5, S → 3: option C

Simulation ID

• ADV-2026-P1-CHE-Q15 · revision 1

See this simulation in the library →  ·  open the simulation file on its own