ChemistryHaloalkanes and haloarenesClass 12

Organic reaction mechanisms (SN1 & SN2): interactive simulation

Nucleophilic substitution and elimination reactions form the core of organic reaction mechanisms in JEE and NEET. Subtle changes in substrate branching, nucleophile strength, base size and solvent completely pivot the reaction pathway.

Useful for: JEE Main, JEE Advanced, NEET, CBSE Boards · 3 modes in one lab

What you can explore

  1. 1

    SN1 vs SN2 Substitution Race

    Concerted backside attack with inversion vs carbocation intermediate with racemization.
  2. 2

    E1 vs E2 Elimination (Saytzeff)

    Saytzeff more substituted alkene vs Hofmann bulky base elimination.
  3. 3

    Markovnikov vs Anti-Markovnikov

    Electrophilic addition of HBr to propene with and without organic peroxides.

Try this

Explore concerted backside attacks in SN2 that flip molecular stereochemistry like an umbrella, step-by-step carbocation intermediates in SN1 that yield racemic mixtures, and Saytzeff versus Hofmann elimination selectivity.

  1. 1

    Switch from SN2 to SN1.

    What you should see

    SN2 shows a single-step concerted backside attack with Walden inversion, while SN1 produces a planar sp² carbocation open to front and back attack (racemization).

  2. 2

    In Elimination, switch base from Small Base (alc. KOH) to Bulky Base (t-BuOK).

    What you should see

    Major product flips from But-2-ene (Saytzeff, 81%) to But-1-ene (Hofmann, 80%) because the bulky base cannot access the crowded secondary carbon.

  3. 3

    In Alkene addition, toggle Organic Peroxide on.

    What you should see

    Addition of HBr to propene flips from 2-bromopropane (Markovnikov) to 1-bromopropane (Anti-Markovnikov Kharasch effect).

Formulas behind it

SN2 rate law (Bimolecular)

Rate=k[Substrate][Nucleophile](Order: CH3X>1∘>2∘≫3∘)\text{Rate} = k [\text{Substrate}] [\text{Nucleophile}] \quad (\text{Order: } \text{CH}_3\text{X} > 1^\circ > 2^\circ \gg 3^\circ)

SN1 rate law (Unimolecular)

Rate=k[Substrate](Order: 3∘>2∘>1∘)\text{Rate} = k [\text{Substrate}] \quad (\text{Order: } 3^\circ > 2^\circ > 1^\circ)

Saytzeff alkene stability (Hyperconjugation)

Stability∝Number of α-hydrogens\text{Stability} \propto \text{Number of } \alpha\text{-hydrogens}

Common mistakes

  • Applying the peroxide effect to HCl or HI. Kharasch peroxide effect works ONLY for HBr, because H-Cl bond is too strong (step 1 endothermic) and I· radical prefers dimerization over alkene addition.
  • Assuming SN1 always gives 100% racemic mixture — slight excess of inversion is often observed due to intimate ion-pair shielding.
  • Using polar protic solvents for SN2. Protic solvents hydrogen-bond to nucleophiles, reducing their nucleophilicity; polar aprotic solvents (Acetone, DMSO) accelerate SN2.
Stuck on a organic reaction mechanisms (sn1 & sn2) question?Snap it and get a whiteboard video solution.

FAQ

Why do tertiary halides undergo SN1 so rapidly?

Because the 3° carbocation intermediate is strongly stabilized by 9 hyperconjugative α-hydrogens and inductive (+I) donation.

What is Walden inversion?

The stereochemical inversion of configuration occurring during SN2 reactions when a nucleophile attacks from the side opposite to the leaving group.

What is the role of alcoholic KOH in dehydrohalogenation?

Alcoholic KOH provides ethoxide ions (C₂H₅O⁻), a much stronger base than aqueous OH⁻, favoring E2 elimination over substitution.

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