Chemistry Class 11 Chapter 13. Hydrocarbons | Page 9

Structure of double bond : -
Preparation : -
From Alkynes : - Alkynes on partial reduction with Partially deactivated palladised charcoal known as Lindlar ’ s catalyst give alkynes .
From Haloalkanes : - dehydrohalogenating ( E 2 or 1,2-elimination or Bita-elimination )
H
2
CH
2
1
CH
2
Alc . KOH
CH
2
CH
2
+ KBr + H O
2
Br
H OH H H OH H H H
CC
H H Br H
Slow
–
C C
CC + Br - + H 2O H H H H
H
Br – Transition state
3 . From Dihaloalkanes : - dehalogenation
Zn / HOAC H
H
H
H C
H
C
H
Na
C
H
C
H
+ ZnBr 2
Br
Br
acetone
H
C
H
H
C
H
+ I2 + 2 NaBr