Forward ozonolysis: Alkene + O3 → ozonide → Zn/H2O (reductive) → aldehydes/ketones. H2O2 (oxidative) → carboxylic acids/ketones.

Rules:

• Each C of the C=C becomes a C=O in the product
• R2C= → R2C=O (ketone); RHC= → RCHO (aldehyde); H2C= → HCHO (formaldehyde)
• With oxidative workup: RCH= → RCOOH; H2C= → HCOOH → CO2 + H2O

Reverse ozonolysis (deduce original alkene from products):

1. Write both carbonyl products
2. Remove =O from each and join the two C atoms with =C
3. Reconstruct the alkene

Example: Products are CH3CHO + (CH3)2CO → alkene is CH3-CH=C(CH3)2 (2-methylbut-2-ene)