Question

Difference between sn1 reaction and se1 reaction

Answer 1

Distinction between SN2 and SN1reactions 

Factors

SN2 Reactions

SN1 Reactions

1. Number of steps

                              Θ                          Θ

One: R : L + : Nu → R : Nu + L

                                Slow

Two: 1. R : L ————→ R+ + : L

                                       Fast

2.      R+ + Nu– ———→ R : Nu

3. Reaction rate and order

Second order:

Rate ∝ [Substrate] [Nucleophile] or Rate = K2[RL][:Nu]

First order:

Rate ∝ [Substrate] or Rate = K1[RL]

4. Molecularity

          Bimolecular

                  Unimolecular

5. TS of slow step

    δ–                              δ–

: Nu – – – C – – – : L

                     δ+             δ–

: Nu – – – C – – – : L – – – Nu :

6. Reacting nucleophile

The carbon of the substrate is attacked by the nucleophile, exclusively from the back side.

The nucleophile can attack the carbon of the substrate from both sides. However, the attack from the back side predominates.

7. Stereochemistry

Complete inversion of configuration takes place.

Inversion and retention takes place.

8. Reactivity order of alkyl halides

Methy l>1°>2°>3° halides. (I>Br>Cl>F)

3°>2°>1° > methyl halides. (I>Br>Cl>F)

9. Rearrangement

No rearranged product is formed (except for allylic).

Rearranged products can be formed.

10. Nature of nucleophiles

Favoured by strong and high concentration of nucleophiles.

Favoured by mild and low concentration of nucleophiles.

11. Polarity

Favoured by solvents of low polarity.

Favoured by solvents of high polarity.

12. Reaction rate determining factor

By steric hindrance.

                                                             ⊕

By electronic factor (stability of R).

13. Catalysis

Not catalysed by any catalyst (phase transfer).

Catalysed by Lewis and Bronsted acids, e.g.,

⊕ Ag, AlCl3, ZnCl2 and strong HA.