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