Acid-Base and Donor-Acceptor Chemistry

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Acid-Base and Donor-Acceptor Chemistry

• Chapter 6

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Acids and Bases

• The Major Acid-Base Definitions

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Acids and Bases

• ArrheniusAcid is proton source in water, base
  is hydroxide sourceAcid Base Salt Water
  HCl NaOH ? NaCl H2OWorks in aqueous
  solutions only
• Brønsted-LowryAcid is proton donor, base is
  proton acceptorAcid(1) Base(1) ? Acid(2)
  Base(2) Can this happen without water?
• Conjugate acid-base pairsReaction favors the
  weaker acid/base pairNon-aqueous solvents, gas
  and solid phase reactions

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Acids and Bases

• Solvent system definition If a species can
  autoionize (autodissociate, form a cation and an
  anion), the cation is an acid and the anion is a
  base
• In this system, an acid increases cation and a
  base increases anion
• Water 2 H2O ? H3O OH
• HCl is an acid in this solvent system (increases
  cation) HCl H2O ? H3O Cl

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Protic Acids and Bases
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Protic Acids and Bases

• Kion is K for the autoionization of the pure
  solvent
• Solvent Acid Base pKionH2SO4 H3SO4 HSO4 3.
  4 at 10 ºCH2O H3O OH 14NH3 NH4 NH2 2
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• Acetic acid is acid in water, but base in H2SO4
• CH3CO2H H2SO4 ? HSO4 CH3CO2H2
• Urea is a base in water, but an acid in liquid
  NH3
• (NH2)2CO NH3 ? NH4 (NH2)(NH)CO

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Aprotic Acids and Bases
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Aprotic Acids and Bases

• Aprotic solvent systems BrF3, PCl52 NH3 ? NH4
  NH2-
• 2 BrF3 ? BrF2 BrF42 PCl5 ? PCl4 PCl6
• In BrF3, SbF5 is an acid and KF is a base
• SbF5 BrF3 ? SbF6 BrF2KF BrF3 ? K
  BrF4
• In this definition, Acid Base Solvent
• BrF2 BrF4 ? 2 BrF3Acid Base
  Solvent
• Broader definition - acid/base character is
  related to the solvent

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Lewis Acid-Base TheoryFrontier Orbitals HOMO
and LUMO
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Lewis Acid vs. Lewis Base vs. Oxidation vs.
Reduction
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Lewis Acid vs. Lewis Base vs. Oxidation vs.
Reduction
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Lewis Acid vs. Lewis Base vs. Oxidation vs.
Reduction
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Lewis Acid vs. Lewis Base vs. Oxidation vs.
Reduction
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Measuring Lewis Acid-Base Interaction Strength
via Electronic Spectra
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Hard and Soft Acids and BasesExamples Ionic
Compound Solubility
AgF(s) H2O(l) ? Ag(aq) F-(aq) Ksp
205 AgCl(s) H2O(l) ? Ag(aq) Cl-(aq)
Ksp 1.8 x 10-10 AgBr(s) H2O(l) ? Ag(aq)
Br-(aq) Ksp 5.2 x 10-13 AgI(s) H2O(l)
? Ag(aq) I-(aq) Ksp 8.3 x
10-17 Similarly, solubility Hg2F2 gt Hg2Cl2 gt
Hg2Br2 gt Hg2I2 BUT, LiF lt LiI
MgF2 is less soluble than MgCl2 AlF3 is
less soluble than AgCl3
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Hard and Soft Acids and BasesExamples
Complexation
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Hard and Soft Acids and BasesExamples
Thiocyanate Bonding to Metals
SCN- can bond through S or N S-binding with M
large, polarizable metals like Hg2, Au,
Pd2 N-binding with M smaller, less
polarizable metals Zn2, Ni2
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Hard and Soft Acids and BasesDefinitions
Hard base small, not polarizable Soft base
large, highly polarizable
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Hard and Soft Acids and BasesDefinitions
Hard acid small, not polarizable Soft acid
large, highly polarizable
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Relate to oxoanions.
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