4 . From Alcohols : - Dehydration ( E1 - elimination )
CH3CH2CH2OH
Conc . H2SO4 CH3CH = CH2 + H2O 160 °
CH3CH2CH2CH2OH Al 2 O 3
CH3CH2CH CH2
Mechanism
300 ° C
H +
- OH + CH3 - CH2 - CH2 - OH CH3 - CH2 - CH2 -H2O CH CH CH
2 3 2 2
CH3 CH CH2 H CH3 CH CH2 1 propene
H loss of H 2O OH CH3 C CH CH3 from 1 , 2
1 2
H3C C CH CH position
CH3
2 3
( major )
CH 3 loss of H 2O
CH 3
C
3
CH 2 CH 3 from 1 , 3 position
CH 2 ( Minor )
Chemical Properties : - Addition Reaction : - Alkene show electrophilic addition reaction . 1 . Addition of Hydrogen : -
RCH = CH2
H2 / Ni
RCH2CH3
2 . Addition of Halogens : -
CH2 = CH2 + Br2
CH2 CH2 Br2
CH2 - CH2 | |
CCl4
Br Br
Solvent H2O Solvent
Br — CH2 — CH2 — OH HBr
( Brown colour ) ( Colourless )
3 . Addition of hydrogen halides Addition reaction of HBr to symmetrical alkenes
Addition reaction of HBr to unsymmetrical alkenes takes place according to Markovnikov Rule
Markownikov rule : - negative part of the addendum ( adding molecule ) gets attached to that carbon atom which possesses lesser number of hydrogen atoms . e g