Organic chemistry Presentations

2. Nucleophilic substitution
reactions
• In the C-X bond there is a partial +ve
charge on the carbon atom and -ve on the
halogen atom. Thus nucleophilies attack the
electron deficient carbon resulting in the
displacement of the weaker nucleophile, the
halide ion.

3. The halide ions are substituted only
if the attacking nucleophile is
stronger. As the halide ion itself is a
very weak nucleophile, the
attacking nucleophile should be
stronger than it. The order of
reactivity of various alkyl halides
towards nucleophilic substitution
is:
RI > RBr > RCl > RF

4. SN
1 reaction (substitution
nucleophilic, first order).

5. The first step is slow and is the rate-determining step. As the
nucleophile (Z-) is not involved in the rate-determining step, the
reaction depends only upon the concentration of alkyl halide (RX)
and is, therefore, a first order reaction.
Rate = k [RX]
The order of reactivity depends upon the stability of
carbonium ion formed in the first step. Since the 3°
carbonium ion is most stable, the ionization of tertiary alkyl
halide is favored. The order of reactivity for SN
1 reaction is,
tertiary > secondary > primary

6. SN
2 reaction (substitution
nucleophilic, second order).
This type of reaction occurs in one step through the
formation of transition state as:

7. Here, the rate of reaction depends upon the concentration of
both the alkyl halide and the nucleophile.
The transition state from tertiary alkyl halide is less stable due
to steric hindrance i.e., crowding of bulky groups. The order
of reactivity is: primary > secondary > tertiary.
Nucleophilic reactions of haloalkanes

8. 2.Replacement by alkoxy group
(Formation of ethers) - Williamson Synthesis

9. 3.Substitution by cyano group

10. 4.Substitution by isocyanide
group

11. 5.Substitution by nitrite group

12. 6.Substitution by nitro group

13. 7.Substitution by amino group
(formation of amines)

15. 8.Substitution by carboxyl
group (formation of esters)

16. 9.Substitution by
hydrosulphide group

17. 10.Substitution by mercaptide
group

18. 11.Substitution by alkynyl
group (formation of alkynes)

19. Haloarenes are lesser reactive towards nucleophilic
reactions than haloalkanes due to following reasons :
1.Resonance effect