Using Structure to Predict AcidityBasicity Using Structure to Predict AcidityBasicity Strong acid relatively unstable acid relatively stable conjugate base Weak acid relatively stable acid relatively
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Using Structure to Predict AcidityBasicity Using Structure to Predict AcidityBasicity Strong acid relatively unstable acid relatively stable conjugate base Weak acid relatively stable acid relatively

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Using Structure to Predict AcidityBasicity Using Structure to Predict AcidityBasicity Strong acid relatively unstable acid relatively stable conjugate base Weak acid relatively stable acid relatively




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Presentation on theme: "Using Structure to Predict AcidityBasicity Using Structure to Predict AcidityBasicity Strong acid relatively unstable acid relatively stable conjugate base Weak acid relatively stable acid relatively"— Presentation transcript:


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Using Structure to Predict Acidity/Basicity Using Structure to Predict Acidity/Basicity Strong acid relatively unstable acid relatively stable conjugate base Weak acid relatively stable acid relatively unstable conjugate base Strong base relatively unstable base relatively stable conjugate acid Weak base relatively stable base relatively unstable conjugate acid Effect of Structure on Effect of Structure on 2. Electronegativity of the atom attached to H the more EN the attached atom, the more acidic the molecule C < N < O < F relative electronegativity CH < NH < HO < F relative stability of conjugate bases CH < NH < H O < HF relative acidity 1. Charged vs. noncharged species a charged molecule is more acidic than a neutral molecule = 15.5 = 40 CH OH CH NH vs a = 36 = 9.4 NH 4 + NH 3 NH 3 NH 2 + + + + 1
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Effect of Structure on Effect of Structure on II II 3. Size of attached atom the larger the attached atom, the more acidic (down column) I > Br > Cl > F relative size > Br > Cl > F relative stability of conjugate bases HI > HBr HCl > HF relative acidity 4. Inductive electron withdrawal a. Magnitude of electronegativity (the more EN, the more acidic) b. Distance away from (-) charged conjugate base (closer = more acidic) = 4.76 = 3.15 = 2.86 = 2.81 = 2.66 O C O C 2 I O C 2 r O C 2 l O C 2 F Example: N vs O vs S Example: N vs O vs S Nitrogen is most effective at stabilizing a positive charge and least effective at stabilizing a negative charge Sulfur is most effective at stabilizing a negative charge and least effective at stabilizing a positive charge C S H H C O H H C N H H H C N H H C O C S H = -6.8 = -2.4 = 9.8 = 10.6 = 15.9 = 35 2
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Effect of Structure on Effect of Structure on III III 5. Hybridization ( sp , sp , sp ) sp 50% character sp 2 33% character sp 3 25% character > > Relative Acidity C H C H C H H C C H > > = 25 = 44 = 50 Conjugate base has negative charge, which is stabilized by orbitals with greater character Effect of Structure on Effect of Structure on IV IV electron delocalization 6. Resonance resonance stabilizes the negative charge of the conjugate base the more resonance contributors, the more stable the molecule C O C C + + O C O C + + = 15.9 = 4.76 3