Reactions of Unsaturated Hydrocarbons

Combustion

• Complete combustion

C3H6 + O2 → CO2 + H2O

• Incomplete combustion

C3H6 + O2 → C + CO + CO2 + H2O

Combustion

• Complete combustion

2 C3H6 + 9 O2 → 6 CO2 + 6 H2O

• Incomplete combustion

C3H6 + 3 O2 → C + CO + CO2 + 3 H2O

Addition Reactions• Take place on unsaturated compounds because

they contain double or triple bond

• Two atoms are added to carbons joined in multiple bond

• What can be added?– X2 H2 H2O HX

Addition

• Addition of halogen– Alkenes form dihaloalkanes

CH3 – CH = CH – CH3

CH3 – CH = CH2

+ Cl2

+ Br2

Solution is on the next slide

Addition on Alkene

Addition on Alkyne

• Alkynes produce dihaloalkenes or tetrahaloalkanes

CH3 – C ≡ C – CH3

CH3 – CH2 – C ≡ CH

+ Cl2

+ Br2

Solution is on the next slide

Addition on Alkyne

Addition

• Addition of Hydrogen– Catalysts normally used such as Pt, Pd or Ni

• Known as Hydrogenation– Alkene becomes an alkane– Alkyne becomes and alkene or alkane

H2C=CH2 + H2 Heat, catalyst

H HH-C-C-H H H

Hydrogenation

CH3 – C ≡ C – CH3

CH3 – CH2 – C ≡ CH

CH3 – CH = CH2 + H2

+ H2

+ H2

Solution is on the next slide

Hydrogenation

Addition

• Addition of Water– Occurs in the presence of acid (H+)

• Known as Hydration– Alkene becomes an alcohol– Alkynes do not produce alcohols this way! (produces ketone or aldehyde)

Hydration

CH3 – CH = CH – CH3 + H2O

Addition of H2O on Asymmetrical Alkenes

• Asymmetrical alkenes – an alkenes that has different groups on either side of the double bond

CH3 – CH = CH – CH3 symmetric

CH3 – CH2 – CH = CH2 asymmetric

Markovnikov’s Rule

• States that the carbon with most hydrogen atoms receives even more hydrogen atoms in an addition reaction

• According to the Markovnikov’s rule, the addition of two asymmetrical reactants forms primarily one product.

• Only small amount of the other isomer is found.

CH3 – CH2 – CH = CH2 + H2O

CH3 – CH = CH2 + H2O

Solution is on the next slide

Hydration

Addition

• Addition of Hydrogen Halides (HX)– HX = HCl, HBr, HI (Not HF)– Alkene becomes an alkyl Halide– Alkynes form monohalo alkenes or dihaloalkanes with the halogens on the same carbon

H2C=CH2 + HX H HH-C-C-H H X

HC=CH + HX

H-C=C-H H X

H XH-C- C-H H X

+ HX

Addition of HX on Asymmetrical Alkenes

• Markovnikov’s Rule applies

CH3 – CH2 – CH = CH2 + HBr