Reactions of Unsaturated Hydrocarbons

Combustion Complete combustion C 3 H 6 + O 2 → CO 2 + H 2 O Incomplete combustion C 3 H 6 + O 2 → C + CO + CO 2 + H 2 O

Combustion Complete combustion 2 C 3 H O 2 → 6 CO H 2 O Incomplete combustion C 3 H O 2 → C + CO + CO H 2 O

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? – X 2 H 2 H 2 OHX

Addition Addition of halogen – Alkenes form dihaloalkanes CH 3 – CH = CH – CH 3 CH 3 – CH = CH 2 + Cl 2 + Br 2 Solution is on the next slide

Addition on Alkene

Addition on Alkyne Alkynes produce dihaloalkenes or tetrahaloalkanes CH 3 – C ≡ C – CH 3 CH 3 – CH 2 – C ≡ CH + Cl 2 + Br 2 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 H 2 C=CH 2 + H 2  Heat, catalyst H H H-C-C-H H H

Hydrogenation CH 3 – C ≡ C – CH 3 CH 3 – CH 2 – C ≡ CH CH 3 – CH = CH 2 + H 2 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 CH 3 – CH = CH – CH 3 + H 2 O

Addition of H 2 O on Asymmetrical Alkenes Asymmetrical alkenes – an alkenes that has different groups on either side of the double bond CH 3 – CH = CH – CH 3 symmetric CH 3 – CH 2 – CH = CH 2 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.

CH 3 – CH 2 – CH = CH 2 + H 2 O CH 3 – CH = CH 2 + H 2 O 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 H 2 C=CH 2 + HX  H H H-C-C-H H X HC=CH + HX  H-C=C-H H X H-C- C-H H X + HX 

Addition of HX on Asymmetrical Alkenes Markovnikov’s Rule applies CH 3 – CH 2 – CH = CH 2 + HBr