Chapter 3: Acids and Bases 3.1 Introduction to Brønsted- Lowry Acids and Bases Arrhenius definition

Acid - substance that ionizes to give a proton (H+) when dissolved in water Base - substance that ionizes to give hydroxide (HO-) when dissolved in water

Bronsted-Lowry definition Acid - proton donor Base - proton acceptor

B: + H–A +B–H + :A– base acid conjugate conjugate

acid base

H2O: + H–Cl H2O–H + :Cl– hydronium

ion

+

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B: + H–A +B–H + :A– base acid

H2O: + H–Cl H2O–H + :Cl– +

3.2 Flow of Electron Density: Curved- Arrow Notation

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3.3 Brønsted- Lowry Acidity: Quantitative Perspective H2O + H–A H3O + A– +

Keq= __________ [H3O+] [A−] [H-A] [H2O]

Keq [H2O] = = Ka acid dissociation constant __________ [H3O+] [A−] [H-A]

pKa = –log Ka

pH = –log [H3O+]

In dilute solution, the H2O concentration is constant (~55.5 M) and is therefore incorporated into the Ka

The lower the pKa value, the stronger the acid strength.

The conjugate base of a weak acid is a strong base.

The conjugate base of a strong acid is a weak base. 45  

Table 3.1 (p. 102)

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Henderson-Hasselbalch Equation: Relates pKa with pH

pH = pKa + log   [A−] [H-A] ______

pKa and the position of equillibrium

(H3C)3C-O–H + –OH (H3C)3C–O– + H–OH pKa= 18 pKa= 15.7

HC≡C–H + –OH HC≡C– + H–OH pKa= 25 pKa= 15.7

O-H

+ –OH + H–OH pKa= 10 pKa= 15.7  

O

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3.4 Brønsted- Lowry Acidity: Qualitative Perspective

H–A H+ + :A– The acidity of an acid H-A is reflective of the stability of the conjugate base A–. Consider the atom bearing the negative charge. The ability of an atom to stabilize negative charge increases across a row (from left to right), and down a period.

H–F H–Cl H–Br H–I pKa 3.1 -3.9 -5.8 -10.4

            H–CH3 H–NH2 H–OH H–F

pKa ~50 38 5.7 3.1

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Resonance. Resonance delocalization of negative charge is stabilizing. Inductive effects. Electron withdrawing groups can stabilize negative charge.

H3C H2C O H + H2O H3C H2C O + H3O

H3C CO

O H+ H2O H3C C

O

O+ H3O

pKa ~4.7

pKa ~16

H3C H2C O HpKa ~16

F3C H2C O HpKa ~11.3

H3C CO

O HpKa ~4.7

F3C CO

O HpKa ~0.5

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Orbitals that holds the electron pair. Orbitals with greater S-character are better able to stabilized the negative charge.

sp > sp2 > sp3

C C

H

H H

H

HC C H H3C CH2 H

pKa 25 44 ~50

3.5 Position of Equilibrium and Choice of Reagents (Please read) 3.6. The Leveling Effect (Please read)

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3.7 Solvating Effects. The efficiency by which H2O can solvate H+ and A– can affect the pKa of H–A 3.8 Counterions (please read) 3.9 Lewis Acids and Bases

Acid - an electron pair acceptor Base - an electron pair donor.  

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Chapter 4: Alkanes and Cycloalkanes 4.1 Introduction to alkanes Hydrocarbon: molecules that contain only carbon and hydrogen

1. Aliphatic – open chain hydrocarbons a. alkanes - contain C-C single bonds - CnH(2n+2) b. alkenes - contain C=C double bonds - CnH(2n) c. alkynes - contain CΞC triple bonds - CnH(2n-2)

2. Cycloalkanes - CnH(2n)

3. Arenes (aromatics) - cyclic hydrocarbons with alternating C-C single and double bonds

C C CC

H

H H

H

C

H

H

H

H

H

H

H

H

hexane 1-hexene1-hexyne benzenecyclohexane

saturated hydrocarbons

unsaturated hydrocarbons

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