In the Cannizzaro reaction, aldehydes that do not possess an $\alpha$-hydrogen atom undergo self-oxidation and reduction (disproportionation) upon treatment with a concentrated alkali to form a primary alcohol and a carboxylic acid salt. No new carbon-carbon bonds are formed in this process.

In contrast:

• The Wurtz reaction couples two alkyl halides in the presence of sodium to form a higher alkane, creating a new C-C bond.
• Friedel-Crafts acylation introduces an acyl group ($\text{R-CO-}$) to an aromatic ring, creating a new C-C bond.
• The Reimer-Tiemann reaction introduces a formyl group ($\text{-CHO}$) to a phenol ring, also creating a new C-C bond.