Reference Reaction Summary Tables Addition vs. Substitution at Carbonyls — A Direct Comparison
Addition vs. Substitution at Carbonyls — A Direct Comparison
Estimated reading time: 1 min
In this section
- Overview
- Substitution and Elimination (SN1, SN2, E1, E2)
- Addition to Alkenes and Alkynes
- Nucleophilic Addition to Aldehydes and Ketones
- Nucleophilic Acyl Substitution (Carboxylic Acid Derivatives)
- Enols, Enolates, and Carbon–Carbon Bond Formation
- Electrophilic Aromatic Substitution
- Addition vs. Substitution at Carbonyls — A Direct Comparison
- Cross-References
This is one of the most frequently confused pairs in Organic Chemistry II. Both reactions begin identically — a nucleophile attacks the electrophilic carbonyl carbon, forming a tetrahedral intermediate — but what happens next depends entirely on what else is attached to that carbon.
| Aldehydes/Ketones (Chapter 12) | Carboxylic Acid Derivatives (Chapter 13) | |
|---|---|---|
| Leaving group on carbonyl carbon? | No (only H or R groups) | Yes (Cl, OR, OCOR, NR₂) |
| Fate of the tetrahedral intermediate | Protonated to give a stable alcohol (or hemiacetal) | Collapses, ejecting the leaving group and reforming C=O |
| Net transformation | Addition (C=O becomes C–OH, no atoms lost) | Substitution (one heteroatom group replaces another) |
Reasoning through this table only requires one question: is there a leaving group already attached to the carbonyl carbon? If not, addition is the outcome; if so, substitution is.