ALKENES AND CYCLOALKENES
Most of the addition reactions is regio a stereospecific, but some of them are not stereospecific.
Addice of H2O  /  H+
Markovnikov  rule (regioselective reaction)
Adice H2SO4
Markovnikov  rule (regioselective reaction)
Similarly also addition of hydrohalogenates
nonstereospecific
nonstereospecific
nonstereospecific

ALKENES AND CYCLOALKENES
nonstereospecific
Ozonization
Reaction examples:
The ozonides are decomposed by catalytic hydrogenation or by treatment by dimethylsufide

ALKENES AND CYCLOALKENES
Stereospecific reactions  cis- (syn)-
Hydrogenation
during reaction enantiomers    are formed
Olefin may attack the catalyst also by the other side

ALKENES AND CYCLOALKENES
Stereospecific reactions  cis- (syn)-
Oxidation by KMnO4   or  OsO4
enantiomers
Similar is reaction with OsO4

Stereospecific reactions  cis- (syn)-
ALKENES AND CYCLOALKENES
Epoxidation
Peroxyacid may come also  from the other side
epoxide
Epoxides are not stable  =  reactive  compounds – in an acidic medium we are able to transfer them
to dioles
The splitting of the epoxides proceeds under formation of trans- dioles

ALKENES AND CYCLOALKENES
Stereospecific reactions  cis- (syn)-
Hydroboration        B2H6                      2 BH3
The result of the reaction is the same as after addition of water in an acidic medium but the
regioselectivity is contrary
+ enantiomer
Markovnikov rule (regioselective reaction)

ALKENES AND CYCLOALKENES
Stereospecific reactions  cis- (syn)-


ALKENES AND CYCLOALKENES
Stereospecific reaction cis- (syn)-
Oxymercuration – demercuration   (reaction with mercury acetate, Hg2+ is the electrophile)
Demercuration is carried out by NaBH4
Markovnikov rule (regioselective reaction)

ALKENES AND CYCLOALKENES
!! Under radical conditions the regioselectivity during addition of hydrohalogens is changing!!!
KHARASH  phenomenon  =  antimarkovnikov  rule
catalysis by UV light ( hn) , radicals, heat
more stable than
initiation
propagation

ALKENES AND CYCLOALKENES
At radical conditions you can expect also additions of :
chlorine, bromine, sulfane, thioles a polyhalogenated alkanes
iniciation

ALKENES AND CYCLOALKENES
POLYMERIZATION
mechanism: radical polymerization
                       ionic polymerization  -  kationic
          - anionic
iniciation
propagation
termination

ALKENES AND CYCLOALKENES
POLYMERIZATION
Kationic polymerizations, catalysis by BF3, TiCl4, R3Al ……
Monomers for the most important polymers

ALKENES AND CYCLOALKENES
POLYMERIZATION
Anionic polymerizations, catalysis by strong bases: BuLi, NaNH2…
This method is suitable for alkenes with electronwithdrawing groups, where that group enables
entrance of the base and stabilisation of formed anion.
mechanism of the second glue action

ALKENES AND CYCLOALKENES
Notice higher reactivity of hydrogenatoms  at Csp3 in neighbourghood of double bond
Hydrogen atoms at allylic position are reactive in radical reactions (the formed radical is
stabilized by the double bond next to it)
In allylic position you can realize halogenation without loss of double bond (without addition)
The suitable halogenation agent is NBS (NCS)
~