2 2-1 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Introduction to Organic Chemistry 2 ed William H. Brown

2 2-2 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. AcidsandBases

2 2-3 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Brønsted-Lowry Definitions Acid: a proton donor Base: a proton acceptor

2 2-4 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Conjugate Acids & Bases When an acid donates a proton, it is converted to its conjugate base When a base accepts a proton, it is converted to its conjugate acid

2 2-5 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Strong Acids and Bases Strong acid - completely ionized in aqueous solution. Examples are: HCl, HBr, HI, HNO 3, HClO 4, and H 2 SO 4 Strong base - completely ionized in aqueous solution. Examples are: LiOH, NaOH, KOH, Ca(OH) 2, and Ba(OH) 2

2 2-6 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Weak Acids and Bases Acetic acid is a weak acid it is incompletely ionized in aqueous solution

2 2-7 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Weak Acids and Bases The equation for the ionization of a weak acid, HA, in water and the acid ionization constant, K a, for this equilibrium are

2 2-8 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Weak Acids and Bases

2 2-9 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Structure & Acidity Electronegativity the relative acidity of HA within a period is determined by the stability of A - the greater the electronegativity, the greater the stability of A -

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Structure & Acidity Resonance - delocalization of charge in A - carboxylic acids and alcohols both contain an -OH group a carboxylic acid is a stronger acid than an alcohol

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Structure & Acidity Resonance - delocalization of charge in A - delocalization of charge stabilizes the carboxylate ion relative to the alkoxide ion

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Structure & Acidity Inductive effect the electron-withdrawing inductive effect of the adjacent carbonyl group weakens the O-H bond of the carboxylic acid Carboxylic acids are more acidic than alcohols delocalization of charge in the carboxylate ion electron-withdrawing inductive effect of adjacent C=O

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Position of equilibrium Favors reaction of the stronger acid and stronger base to give the weaker acid and weaker base

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Position of equilibrium Stronger acid and stronger base react to give weaker acid and weaker base

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Position of equilibrium Stronger acid and stronger base react to give weaker acid and weaker base

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Lewis Acids and Bases Lewis acidLewis acid: accepts a pair of electrons to form a new covalent bond Lewis baseLewis base: donates a pair of electrons to form a new covalent bond

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Lewis Acids and Bases

Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Acids and Bases End Chapter 2