| SN1 |
SN2 |
| 1. These are first order reactions. |
These are second order reactions. |
| 2. The nucleophile can attack from the back side as well as from the front side, however the former predominates. |
The nucleophile can attack only from the back side. |
| 3. Partial recemisation takes place in case of optically active alkyl halides. |
Walden inversion takes place. |
| 4. Reaction rate is influenced by electronic factors. |
Reaction rate is determined by steric factors. |
| 5. Rearrangement is possible. |
Rearrangement is not possible. |
| 6. The order of reactivties of alkyl halides is : Benzyl, Allyl > 3° > 2° > 1° > Methyl halides |
Rearrangement is not possible. : The order of reactivities is: Methyl > 1° deg > 2° deg > 3° deg halides |
| 7. Tertiary alkyl halides are the common substrates, i. e. the presence of bulky groups facilitates SN1 reaction. |
Primary alkyl halides are the common substrates, i. e. the presence of simple and fewer R groups facilitates SN2 reaction. |
| 8. Favoured by mild nucleophiles e.g. alcohols, water, etc. |
Favoured by strong nucleophilies, e.g. alkoxide ion. |
| 9. Favoured by the low concentration of the nucleophiles. |
Favoured by the high concentration of the nucleophiles. |
| 10. Favoured by polar solvents. |
Favoured by non-polar or low polarity solvents. |
| 11. Favoured by the presence of electrophilic cataysts. |
Favoured by the absence of electrophilic catalysts. |
