SN1 reactions follow first-order kinetics. They proceed through a carbocation intermediate and can undergo carbocation rearrangement. The reaction is non-stereospecific, resulting in a racemic mixture of products with 50% inversion and 50% retention of configuration. Carbocation stability is influenced by inductive, hyperconjugation, and resonance effects. The reactivity of the substrate depends on the stability of the carbocation and follows the order of tertiary > secondary > primary > methyl substrates. The reaction requires a good leaving group and is favored in polar protic solvents.

1. MR.DHIRAJKUMAR S.NIKAM
ASST.PROFESOR
Pharmaceutical Chemistry
Bharati Vidyapeeth College of
Pharmacy Navi Mumbai
India
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SN1 Reaction

2. SN1 Reaction
 Contents :
• Features of SN1 reaction
• SN1 Mechanism
• Stereochemistry
• Carbocation stability
• Carbocation rearrangement
• Factors affecting SN1 reaction
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3. SN1 Reaction
 Features:
• Follows first order kinetics
• Racemization
• Non-stereospecific
• Carbocation rearrangement
• Reactivity sequence of substrate 3o > 2o > 1o > CH3W
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4. SN1 Reaction Mechanism
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Example
Rate= k[RBr] follows first order kinetics
Mechanism

5. SN1 Stereochemistry
Step 1
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Step 2

6. SN1 Reaction Mechanism
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Energy diagram

7. Carbocation stability
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Structure of carbocation : Trigonal Planar
Stability of carbonations

8. Carbocation stability
• Three factors affects carbocation stability:
1. Inductive effect
2. Hyper conjugation effect
3. Resonance
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9. Carbocation stability
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Stability order
Resonance

10. Carbocation Rearrangement
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Alkyl Shift
Hydride Shift

11. Carbocation Rearrangement
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Alkyl shift ring expansion
Aryl Shift

12. Factors affecting SN1 reaction
All carbocations are very good electrophiles and even weak
nucleophile will react quickly with them.
e.g. H2O and CH3OH
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SN1 relative reactivity
R3CX >R2CHX > RCH2X > CH3
3o 2o 1o Methyl
Relative rate >106 1 < 10-4 < 10-5
I. Nature of substrate
II. Nature of nucleophile

13. Factors affecting SN1 reaction
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III. Effect of leaving group
IV. Solvent effect

14. Factors affecting SN1 reaction
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V. Order of leaving group
H
O
H
water
CH3
O
HO
acetic acid
H3C OH
methanol
H2
C
CH3
HO
ethanol
H
C
O
HO
formic acid
> > > >
V. Order of polar protic solvents

15. Summary SN1 reaction
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Overall summary
Kinetics Follow first order kinetics
Rearrangement Undergoes carbocation rearrangement
Product 50 % Inversion
50 % Retention
Forms racemic mixture
Nucleophile Unimportant, any weak nucleophile can perform
reaction
Leaving group Important , requires best leaving group
Solvents Important , requires polar protic solvent

16. References
1. Organic Chemistry by R.T. Morrison and R. N.
Boyd, 7th edition.
2. Organic Chemistry by Pine, Stanley H.;
Hendrickson, James B.; Cram, Donald J.;
Hammond, George S., 5th edition.
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