8A, Chapter 2

CHEM 8A, Lecture 3 – Acid-Base Chemistry - Lewis & Bronsted-Lowry Acids & Bases - Curved Arrow Mechanisms - Products of Acid-Base Reactions & Direction of Equilibrium - Acid Strength

Acid-Base Reactions  fastest reactions in organic chemistry!

Bronsted-Lowry Lewis Proton (H+) movement Electron (e-) movement

Acids Donate H+ Accept Electrons

Bases Accept H+ Donate e-

Simple inorganic titrations…

HCl + NaOH  H2O + NaCl

Full ionic equation & curved arrow notation (reaction mechanism)

Ka, acid-dissociation constant, HA  H+ + A- pKa, affinity of an acid for its proton pKa = - log Ka stronger acid weaker acid  pKa =  affinity for its proton  pKa,  affinity for its proton doesn’t need its proton needs its proton more stable conjugate base less stable conjugate base

Acid-base reaction in cookies!

+ + + NaHCO3 + H  Na + H2CO3  Na + H2O + CO2

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8A, Chapter 2

ORGANIC ACID-BASE REACTION

O H + HN(CH3)2 O dimethylamine acetic acid

Equilibrium favors weaker acid ( pKa when comparing acid vs. conjugate acid)

pKa’s to Memorize

Explaining relative acidity

Compare HCl HAc H2O

Conjugate base

Predicting Products in Acid-Base Reactions - Use pKa’s to identify acid & base, where applicable - Remove most acidic H+ from acid, give it to the base - Add formal charges where appropriate

HCl + HAc 

CH3OH + CH3NH2 

CH3OH + H2SO4 

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8A, Chapter 2

Ranking Acids

1. Organize / categorize by pKa reference standard (functional group)

O OH OH OH F 2 F F Ex. OH F

2. Within each category from #1, organize by stability of conjugate base

Increasing Conjugate Base (CB) Stability ☹ Destabilizing CB

- Stabilize (-) charge on larger atom - Donate more e- into negative charge or with nearby EN atoms ** Alkyl groups inductively donate - Stronger acids have more stable CB - Weaker acids have less stable CB

Size EN

HCl vs. HF O O O O F Cl OH OH OH OH

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8A, Chapter 2 pKa Game Color each box in the indicated color. Indicate the relative acidity of each by labeling each as < or > the pKa standard in that family.

Color water & alcohols in pink:

H2O

(pKa 16)

Color haloacids (inorganic) in green:

HCl HBr HF HI (pKa -7)

Color carboxylic acids in yellow:

Next time… - Functional groups, alkane nomenclature, conformational analysis ** Take ~30 min to skim Chapter 3, use Reading Questions!

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