Chapter 11 Unsaturated Hydrocarbons 11 3 Addition Reactions

Chapter 11 Unsaturated Hydrocarbons 11. 3 Addition Reactions 1

Addition Reactions In alkene and alkynes • The double or triple bond is easily broken, which makes double and triple bonds very reactive. In addition reactions, reactants are added to the carbon atoms in the double or triple bond. 2

Hydrogenation In hydrogenation, • Hydrogen atoms add to the carbon atoms of a double bond or triple bond. • A catalyst such as Pt or Ni is used to speed up the reaction. 3

Hydrogenation of Oils Adding H 2 to double bonds in vegetable oils produces • Compounds with higher melting points. • Solids at room temperature such as margarine, soft margarine, and shortening. 4

Learning Check Write an equation for the hydrogenation of 1 -butene using a platinum catalyst. 5

Solution Write an equation for the hydrogenation of 1 -butene using a platinum catalyst. Pt CH 2=CH─CH 2─CH 3 + H 2 CH 3─CH 2─CH 3 6

Trans Fats In vegetable oils, the unsaturated fats usually contain cis double bonds. • During hydrogenation, some cis double bonds are converted to trans double bonds (more stable) causing a change in the fatty acid structure. • If a label states “partially” or “fully hydrogenated”, the fats contain trans fatty acids. 7

Learning Check (1) True or (2) False A. ____ There are more unsaturated fats in vegetable oils. B. ____ Hydrogenation converts some cis-double bonds to trans- double bonds. C. ____ Animal fats have more unsaturated fats. 8

Solution (1) True or (2) False A. 1 There are more unsaturated fats in vegetable oils. B. 1 Hydrogenation of oils converts some cis-double bonds to trans- double bonds. C. 2 Animal fats have more unsaturated fats. 9

Learning Check Write the product of each the following. Pt CH 3─CH=CH─CH 3 + H 2 Pt + H 2 10

Solution Pt 1. CH 3─CH=CH─CH 3 + H 2 2. + H 2 CH 3─CH 2─CH 3 Pt 11

Hydration In the addition reaction called hydration, • an acid H+ catalyst is required. • water (HOH) adds to a double bond. • an H atom bonds to one C in the double bond. • an OH bonds to the other C. H OH H+ │ │ CH 3─CH=CH─CH 3 + H─OH CH 3─CH─CH─CH 3 12

Hydration When hydration occurs with a double bond that has an unequal number of H atoms, • the H atom bonds to the C in the double bond with the more H. • the OH bonds to the C in the double bond with the fewer H atoms. OH H H+ │ │ CH 3─CH=CH 2 + H─OH CH 3─CH─CH 2 13

Learning Check Write the product for the hydration of each of the following: H+ 1. CH 3─CH 2─CH=CH─CH 2─CH 3 + HOH CH 3 │ H+ 2. CH 3─C=CH─CH 2─CH 3 + HOH H+ 3. + HOH 14

Solution 1. 2. H OH │ │ CH 3─CH 2─CH─CH─CH 2─CH 3 │ CH 3─C─CH─CH 2─CH 3 │ │ OH H OH 3. H 15