Fatty Acids Unbranched carboxylic acids with 12-20 carbons. Most contain an even number of carbons because they are built from acetic acid units. Melting points increase with increasing molecular weights. Unsaturation greatly lowers the melting point. => Chapter 25 6
Chapter 25 6 Fatty Acids • Unbranched carboxylic acids with 12-20 carbons. • Most contain an even number of carbons because they are built from acetic acid units. • Melting points increase with increasing molecular weights. • Unsaturation greatly lowers the melting point. =>
Melting Points A cis double bond bends the molecule so it cannot pack efficiently. A trans double bond has less effect. COOH COOH stearic acid,mp 70C oleic acid.mp 4C > Chapter 25 7
Chapter 25 7 Melting Points • A cis double bond bends the molecule so it cannot pack efficiently. • A trans double bond has less effect. =>
Fats and Oils Most fats have saturated fatty acids. Most oils have unsaturated fatty acids. CH,-0-C CHO CH2-0一C tristearin,mp 72C CH2O CH,一0 => triolein,mp-4C Chapter 25 8
Chapter 25 8 Fats and Oils • Most fats have saturated fatty acids. • Most oils have unsaturated fatty acids. =>
Saponification ·“Soap-making' ● Base-catalyzed hydrolysis of ester linkages in fats and oils. 0 CH2-OH -o-(CHCH CH-OH H-0-C-CH6CH3】 CH2-OH +3 NaOH 0 CH2-0-C一(CH2)16CH3 +3Na+0-C-(CH2)16CH => Chapter 25 A soap 9
Chapter 25 9 Saponification • “Soap-making” • Base-catalyzed hydrolysis of ester linkages in fats and oils. CH O C O (CH2 )16CH3 CH2 O C O (CH2 )16CH3 CH2 O C O (CH2)16CH3 + 3 NaOH CH2 CH CH2 OH OH OH + 3 Na+ - O C O (CH2 )16CH3 A soap =>