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Chemistry 2000 Spring 2016 Organic bases (Chapter 16, Sections 16.116.4, 16.7) Tracey Roemmele 1 Organic bases (amines) When you hear the term “organic base”, it’s generally referring to an amine. Amines are readily protonated by acids: H .. N R R base R + ..+ H O H acid N H R + R R conjugate acid + H .. O .. H conjugate base The basicity of amines is due to the lone pair on the nitrogen atom which makes all amines (R = H, alkyl or combination) Lewis bases. 2 Organic bases (amines) We have seen one other functional group containing nitrogen. Why is an amine considered a good base, but an amide is not? The nitrogen atom of an amide is so weakly basic that the oxygen of the carbonyl group will be protonated over it. 3 Quantifying basicity H N H H + H N H pKa = 9.3 H3C + H H pKa = 10.6 4 Quantifying basicity H .. N R R R H + .. O .. H N R + R R .. H .. .. N N H -.. O.. + H H pKb = 4.7 H3C H H pKb = 3.4 5 Calculating pH of a basic solution 6 Calculating pH of a basic solution 7 Amino acids: acid and base ..O .. .. H N H .. C C R H ..O .. H H N H O .. + H C C R .. .O .. . H 8 Amino acids: acid and base 9 Beyond water: implications of acid-base chemistry H C H H .. . O. + .. H C H H .. . ..I . H C H H .. O .. H C H .. + .. ..I .. H 10 Beyond water: implications of acid-base chemistry 11