Deep-Dive Guides · Reactions & Functional Groups
Reactions & Functional Groups — the complete deep dive
There are thousands of organic reactions but only four core reaction types: substitution, elimination, addition, and rearrangement.
Free extract — the opening section of the guide, in full.
0. The four reaction types — the master map
Before any specific reaction, fix the framework. Every reaction rearranges bonds in one of four ways, and the "type" tells you what to look for.
| Type | Net change | Mechanistic sub-classes | Diagnostic question |
|---|---|---|---|
| Substitution | one group replaced by another (σ→σ) | SN1, SN2, SNAr, SRN1, radical | How good is the leaving group? Nucleophile strength? Substrate class? |
| Elimination | two groups lost, π-bond formed | E1, E2, E1cb, Ei (syn) | Base strength/bulk? Anti-periplanar geometry? Acidic β-H? |
| Addition | π-bond consumed, two σ-bonds formed | electrophilic (C=C), nucleophilic (C=O/C≡N), radical, pericyclic | Is the π-bond electron-rich (alkene → electrophile first) or electron-poor (C=O → nucleophile first)? |
| Rearrangement | skeleton/connectivity changes | 1,2-shifts, sigmatropic, ring expansion/contraction | Is there a more stable intermediate one shift away? |
The polarity compass. Alkenes/alkynes are electron-rich (π HOMO high) → they are attacked by electrophiles first (Markovnikov, halogenation). Carbonyls/nitriles are electron-poor at carbon (π* LUMO low, C is δ+) → they are attacked by nucleophiles first. Alkyl halides/tosylates are σ-electrophiles at the carbon bearing the leaving group. Getting the polarity right immediately tells you which mechanism family applies.
Read the rest of this guide
The remaining 8 sections — Nucleophilic substitution, Elimination (E1 / E2 / E1cb) & the E–S competition, Addition reactions, Functional-group interconversions (the FGI map) and more — are part of ChemVidya Full Access, along with the other guides, the books, the study notes and 6,000+ practice questions with worked solutions.