Chemistry Named Reactions: The Families That Repeat
JEE does not test the names for their own sake. It tests the structural transformation attached to each name, and the names are just signposts for which mechanism to run.
A topic note grouping the organic chemistry named reactions by transformation family — substitution, elimination, addition, rearrangement — and the JEE pattern each family follows.
How this actually works
Why named reactions exist in JEE
The named reactions fall into four families that the exam recycles year after year: substitution, elimination, addition, and rearrangement. Learning the family a reaction belongs to is more useful than memorising each reaction in isolation, because the exam almost never asks "name this reaction" — it gives you a substrate and asks for the product.
The substitution family
SN2 flips the configuration and proceeds through a single backside attack, so it is blocked by branching near the reaction centre. SN1 proceeds through a carbocation, so it is blocked by rearrangement and favoured by polar protic solvents. Gabriel synthesis makes a primary amine without rearrangement. Hoffmann elimination gives the least-substituted alkene and demands heat and a bulky base. The test pattern: give the substrate, ask for the product with inversion or elimination. The cue is the geometry of the leaving group's position, not the name.
The elimination and addition families
For elimination, Saytzeff gives the more substituted alkene unless the base is bulky, in which case the Hofmann product flips the selectivity. For addition, the deciding question is always whether the first bond made is to an electron-rich or an electron-poor partner: Markovnikov if rich, anti-Markovnikov if the peroxide effect applies to a hydrogen halide. The named variants — hydroboration-oxidation, ozonolysis — are just signposts for which mechanism story to tell.
The rearrangement family
Wittig replaces a carbonyl with an alkene, with the geometry set by the stability of the ylide. Pinacol moves an OH and a group across a vicinal diol, and the migratory aptitude decides which group moves. In JEE, the question gives a diol and asks which group migrates, and the answer comes from the aptitude order rather than from memory of the named reaction.
How to study them in the time you have
There are around twenty named reactions that appear in the syllabus, and a student with a month cannot memorise twenty mechanism stories. The workable approach is to learn four archetypes — one substitution, one elimination, one addition, one rearrangement — and then reconstruct each named reaction from its reagents. If you know what the reagents do, you can derive the product even if the name has faded.
Chemistry Named Reactions: The Families That Repeat: the facts to keep
| The four families | Substitution, elimination, addition and rearrangement |
|---|---|
| Substitution | SN2 inverts the configuration and is blocked by branching; SN1 goes through a carbocation and rearranges |
| Elimination | Saytzeff gives the more substituted alkene; a bulky base flips it to the Hofmann product |
| Addition | The first bond decides: Markovnikov for an electron-rich partner, anti-Markovnikov under peroxides |
| Rearrangement | Wittig sets alkene geometry from ylide stability; pinacol migration follows migratory aptitude |
| Study advice | Learn four archetypes, one per family, and reconstruct each named reaction from its reagents |
| Migratory aptitude | Aryl > hydride > tertiary alkyl > secondary alkyl > primary alkyl |
Questions students ask about this
How many named reactions do I actually need?
Learn the five that appear in more than one family — SN2, SN1, E1, E2 and Markovnikov — plus the two rearrangements, Wittig and pinacol. The exam asks one substitution, one elimination or addition, and one rearrangement each January, so seven mechanisms cover most of the paper.
What is migratory aptitude?
The order in which groups migrate in a rearrangement. The general order is aryl > hydride > tertiary alkyl > secondary alkyl > primary alkyl, and knowing the order is more reliable than remembering which specific pinacol product forms.