Topic 4: Acids & Bases pt2

Question 1

How to determine Organic Acids & Bases Strength

Answer 1

No math, No calculation, just pure logic

Question 2

How to determine Organic Acids & Bases Strength pt2

Answer 2

Happy=Stable=Unreactive

Unhappy=Unstable= Reactive

We look at the stability of both starting material and products.

Question 3

Reviewing: How to Determine Organic Acids & Bases Strength?

Answer 3

In General HA->H+ + A-
-Stabilizing this anion leads to SA
-Destabilizing this anion leads to WA
Thus, comparing acids, we look at the stability of CB.

B(base) + H+-> BH
-Stabilizing this CA leads to SB
-Destabilizing this CA leads to weak base
Thus, comparing bases we look at the stability of CA

Question 4

Electronegativity

Answer 4

The measure of the ability of an atom to attract shared electrons to itself.
*Larger EN = Attracts more strongly
-Increase across the period (left to right) on PT
-Decrease down group (top to bottom) on PT

Value of H=2.1 E

Question 5

Trend in Atomic Size

Answer 5

Relative atomic sizes for selected atoms
-increase going down
-decrease doing to the right

Question 6

(1) Electronegativity affects Acidity

Answer 6

Ex: CH3OH,CH3NH2,CH3CH3-> Which one is strong acid?

1.Electronegativity of the atom holding the negative charge.

Bottom line: When atoms are the same size, the strongest acid has its hydrogen attached to the most electronegative atom.

The same size= Stronger acid is the one with the most electronegativity.

Question 7

(2) Atomic Size Affects acidity

Answer 7

Ex 2. CH3OH,CH3SH-> Which one is a strong acid?

2. Size of the atom bearing the negative charge in the anion.

Bottom line: When atoms differ in size, the strongest acid has its hydrogen bonded to the largest atom.

Question 8

(3) Resonance Stabilization Affects Acidity?

Answer 8

Ex. Which is the stronger acid between phenol and ethanol?

3. Resonance stabilization, usually of the anion.
   >Increasing resonance stabilization. Increased anion stability.

Question 9

Problem: Which hydrogen is more acidic?

Answer 9

The steps to break down these problems are:

Step 1: Look at the specific atom : Does it have extra lone pairs or a pi bond to break?

Step 2: Draw the conjugated base (separate the H atom from the specific atom)

Step 3: Draw the resonance structures