272_acidity

# 272_acidity - 55.5 K eq = K a = [H 3 O + ][A-] [AH] pK a =...

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Chain Chem 272 Acidity/pKa • Acidity, basicity, and pKa - pKa tells us how acidic (or not) a given hydrogen atom in a compound is, relative to protonated solvent (medium) - More stable conjugate base = stronger acid - Ways to stabilize the conjugate base: • have the charge on an electronegative atom • delocalization of charge over several atoms (better yet, EN atoms) • spread charge over electron-withdrawing groups by induction (polarization) • having the negative charge in an orbital with more s character • gaining aromaticity - It is important to have a working knowledge of some pKa's (table 8.1 in book) AH (aq) + H 2 O (l) H 3 O + (aq) + A - (aq) acid base conjugate acid conjugate base K eq = [H 3 O + ][A - ] [AH][H 2 O] Since [H 2 O] is approx. constant [55.5M], the equation becomes:
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Unformatted text preview: 55.5 K eq = K a = [H 3 O + ][A-] [AH] pK a = –log K a Acid HCl H 2 SO 4 HSO 4-CH 3 CO 2 H NH 4 + CH 3 OH OH H 3 C CH 3 O H NH 3 CH 4 H pKa –7 –3 2.0 4.8 9.2 10.0 15.5 20.0 25 38 ~44 >50 conj. base Cl HSO 4 SO 4 –2 CH 3 CO 2 NH 3 CH 3 O O H 3 C CH 2 O NH 2 CH 3 Rank the following in order of increasing acidity: (1 = least, 4 = most) H 3 C OH O F 3 C OH O OH O Cl F 3 C OH A. B. C. H 3 C OH CH 3 F 3 C OH CF 3 F 3 C OH H 3 C CH 3 NH 2 H 3 C O CH 3 H 3 C O H H 3 C O N(CH 3 ) 2 H 3 C O OCH 3 Where does the equilibrium lie? Label acids and conjugate bases. O OCH 3 H 3 C N Li H 3 C CH 3 H 3 C CH 3 OLi OCH 3 N H H 3 C CH 3 H 3 C CH 3 CH 3 OH KOH OK H 2 O KOH H 2 O O OCH 3 H 3 C OK OCH 3 CH 3 1 2 4 3 1 2 4 3 1 2 4 3...
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## This note was uploaded on 03/07/2011 for the course CHEM 272 taught by Professor Jarrett,j during the Spring '08 term at University of Hawaii, Manoa.

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