Addition rxns of c c multiple bond

1. Department of Chemistry
University of Kashmir
Topic:-Addition Reactions of C-C Multiple Bond
Aadil Ali WAni
Roll no: 16062120001
Teacher Incharge
Prof. Syed Wajahat Amin Shah

2. Addition Reactions of C-C Multiple bond
A chemical reaction of two or more reacting molecular entities,
resulting in a single reaction product containing all atoms of all
components, with formation of two chemical bonds and a net
reduction in bond multiplicity in at least one of the reactants. The
reverse process is called an elimination reaction.
The addition may occur at only one site (α-addition, 1/1/addition),
at two adjacent sites (1/2/addition) or at two non-adjacent sites
(1/3/- or 1/4/addition, etc.). For example:

3. Addition Reaction of Alkene with HBr

4. Addition of HX to Alkenes: Markovnikov’sRule
Markovnikov'srule:in the addition of HX to an alkene, the
hydrogen atom adds to the carbon atom of the double bond that
already has the greater number of hydrogen atoms.

5.  Addition of HX to Alkenes: Markovnikov’sRule

6. Addition of HX to Alkenes: Markovnikov’sRule
Modern statement of
Markovnikov'srule:In the ionic
addition of an unsymmetrical
reagent to a double bond, the
positive portion of the adding
reagent attaches itself to a carbon
atom of the double bond so as to
yield the more stable carbocation
as an intermediate.

7.  Stereochemistry of the Addition of HX to Alkenes

9. Reason
• H-Cl bond is stronger than H-Br Bond. H-Cl is not decomposed by
peroxide-free radical.
• Iodine free radical formed as H-I bond is weaker but iodine-free
radicals readily combine with each other to form iodine molecules
rather than to attack the double bond.
• In H-Br both the chain propagation steps are exothermic and hence
peroxide effect is observed, while in HCl (or HF) the second step is
Endothermic and in HI the first step is endothermic therefore ,
peroxide effect is not observed in HCl or HI.
X ̇ +CH₂=CH₂ CH₂̇ ̶ CH ̶ X (I) X
ΔH(KJ/mole)
Cl -67.0
Br -25.1
I +46.o
Cl +12.6
H ̶ X + X ̶ CH₂ ̶ CH₂̇ X ̶ CH₂ ̶ CH₂ ̶ H +X ̇ (II) Br -
50.2

10. Addition of Sulfuric Acid to Alkenes

11. Addition of Water to Alkenes: Acid-Catalyzed Hydration

12.  Addition of Water to Alkenes: Rearrangement

13. Oxymercuration-Demercuration
 This is another alternative for converting alkenes to alcohols with Markovnikov
orientation. This method has the advantage of not involving free carbocationic
species, and thus removes the possibility of rearrangements.
The reagent is called mercuric acetate, and is usually abbreviated to Hg(OAc)2. In
solution it ionizes into acetate ion and a positively charged mercury species which
is very electrophilic
Oxymercuration is the electrophilic
attack of this species on a double
bond, giving a 3 membered ring
compound called a mercurinium ion.
Oxymercuration-demercuration also gives Markovnikov orientation of the alcohol.

14. Hydroboration of Alkenes
 We have studied three ways of hydrating alkenes to give
Markovnikov orientated alcohols.
 There is also a way to obtain anti-Markovnikov oriented alcohols:
hydroboration.
Borane adds to alkenes with anti-Markovnikov orientation, and these alkylboranes
can then be oxidized to alcohols.
Borane (BH3) itself is unstable, and
exists either as a dimer or as a complex
with THF.

15. Halohydrin Formation
 When the halogenation reaction takes place in the presence of a
nucleophilic solvent, a nucleophile different from the halide can
open the halonium ring.
If the reaction is performed in the presence of water, Halohydrins are produced.
The stereochemistry of the intermediate bromonium ring determines that the final product
must be of anti addition, since ring opening must occur via backside attack.
Orientation of Halohydrin Formation
When propene reacts with chlorine water, the major product has the Cl bound to the less
highly substituted carbon, and hydroxyl to the most highly substituted carbon

16. Addition Reactions of Alkynes
 Many of the reactions of alkynes are similar to those of alkenes
since they both type of compound involve π bonds.
Catalytic Hydrogenation to Alkanes
 Under normal conditions, the reaction cannot be stopped,
producing the alkane.

17. Hydrogenation to cis-Alkenes
 However, It is possible to add only one equivalent of hydrogen to
the triple bond and produce cis alkenes.
 The catalyst used to perform this reaction is known as the
Lindlar’s catalyst.

18.  The mechanism is the same as for hydrogenation of alkenes, but
the catalyst is not active enough (we say that the catalyst is
poisoned) to carry out the hydrogenation of the resulting alkene.
 Gives cis-alkenes since hydrogenation is syn reaction (same side
of triple bond)

19. Reduction to trans-Alkenes
 It is also possible to form trans-alkenes from alkynes. In this case
hydrogen is not involved, and the reduction is carried out with
sodium metal (or lithium) in liquid ammonia by a radical
mechanism)

20. Addition of Halogens
You might expect the mechanism to be similar to the
halogenation of alkenes, yet stereochemical evidence suggests
otherwise.
● The halogenation of an alkene undergoes anti addition ONLY.
● The mechanism for alkyne halogenation is not fully elucidated.

21. Addition of Hydrogen Halides
Similar to the reaction we have seen for alkenes,
When the reaction is performed with a terminal
alkyne, the orientation follows Markovnikov (i.e.
most substituted carbocation is formed).
• Peroxides can be used in the hydrohalogenation of alkynes to
promote anti‐Markovnikov addition just like with alkenes.

22. Addition Reactions ‐ hydration of alkynes
 Internal alkynes undergo hydration with concentrated acid to
form ketones.
• Terminal alkynes require the presence of an additional Hg2+
catalyst (usually HgSO4) to yield methyl ketones by Markovnikov
addition of water.

23. Oxidation
The same reagents that oxidized alkenes
can oxidize alkynes in a similar way.
Using KMnO4 under neutral conditions, a
vicinal diketones are obtained with
internal alkynes.