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R-H + Base  R: - + H-Base

Slides 2 through 6 introduce students to the acidity of terminal alkynes compared to other C-H bonds. R-H + Base  R: - + H-Base. hybridization sp 3 sp 2 sp s character is increasing … a. left to right b. right to left c. no change with hybridization.

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R-H + Base  R: - + H-Base

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  1. Slides 2 through 6 introduce students to the acidity of terminal alkynes compared to other C-H bonds.

  2. R-H + Base  R:- + H-Base hybridization sp3 sp2sp s character is increasing … a. left to right b. right to left c. no change with hybridization

  3. R-H + Base  R:- + H-Base hybridization sp3 sp2sp Stability increasing is … a. left to right b. right to left c. no change with hybridization

  4. R-H + Base  R:- + H-Base hybridization sp3 sp2sp Acidity of the hydrocarbons in blue is increasing …. a. left to right b. right to left c. no change with hybridization

  5. R-H + Base  R:- + H-Base hybridization sp3 sp2sp Basicity of the carbanions is increasing … a. left to right b. right to left c. no change with hybridization

  6. Acid-Base Reactions For H-X the acidity order (ease of giving up a H+) is H-I > H-Br > H-Cl. What is the explanation for this order? a. Electronegativity increases in this order, which means that bond polarity increases in this order. b. Atom size increases causing bond strength to decrease. c. Acid strength decreases with increasing negative charge d. Increasing resonance stabilization

  7. Acid-Base Reactions When an alkene reacts wit H-X, this is also a Lewis Acid-Base reaction. Which is the Lewis acid and which is the Lewis base? • alkene = Lewis acid, H-X Lewis base • alkene = Lewis base, H-X = Lewis acid

  8. Conjugate acids and bases are related through loss and gain of H+ H-Cl ____________________________ of Cl- a. is the conjugate acid b. is the conjugate base c. there is not a conjugate acid-base relationship

  9. Cl- _______________________ of H-Cl • is the conjugate acid • is the conjugate base • there is not a conjugate acid-base relationship

  10. Given the above pKa’s, will the equilibrium for the this reaction be … a. Shifted to the right K >> 1 b. Shifted to the left K << 1 • K ~ 1

  11. Given the above pKa’s, will the equilibrium for the this reaction be … a. Shifted to the right K >> 1 b. Shifted to the left K << 1 • K ~ 1

  12. Which alcohol is more acidic? a. ethanol b. 1,1,1-trifluoroethanol c. approximately equal

  13. Which alcohol would be predicted to be most acidic?

  14. Acid-Base Review • Ka= acid ionization constant (specific property of molecule) • Henderson-Hasselbalch Equation pKa=pH – log [Base] / [Acid] • What does pKa equal when the ratio of base to acid is 1 ? pKa = pH

  15. Lewis Acids and Bases In many cases in this chapter, lone pair electrons will be donated to an “empty orbital”.

  16. Lewis Acids and Bases In the reactions, which are the Lewis bases and which are the Lewis Acids? a. F- and CH3+ are the Lewis acids and H- and BF3 are the Lewis bases. b. F- and H- are the Lewis bases and CH3+ and BF3 are the Lewis acids. c. F- and H- are the Lewis acids and CH3+ and BF3 are the Lewis bases. d. F- and CH3+ are the Lewis bases and H- and BF3 are the Lewis acids.

  17. Interactions of MO’s • Why wouldn’t 2 filled orbitals in the reaction interact? a. There is an orthogonal interaction. b. The overlap would be poor. c. Both a bonding and antibonding orbital would form and they would be filled. There would be no net stabilization. d. They are both antibonding.

  18. Interactions of MO’s • Why wouldn’t 2 filled orbitals in the reaction interact?

  19. Lewis Acids and Bases For this Bronsted Acid – Base reaction, identify the HOMO and LUMO.  a. The LUMO is the filled n orbital on Cl in H-Cl, and the HOMO is the empty s* of the H-O bond. b. The HOMO is the filled n orbital on Cl in H-Cl, and the LUMO is the empty s* of the H-O bond. c. The LUMO is the filled n orbital on O in HO-, and the HOMO is the empty s* of the H-Cl bond. d. The HOMO is the filled n orbital on O in HO-, and the LUMO is the empty s* of the H-Cl bond.

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