Organic Molecules as Acids and Bases (Module 2)

Question 1

What is an organic acid considered? organic base?

Answer 1

acid: proton donor
base: proton acceptor

Question 2

In an equilibrium, what occurs when there is a stronger acid?

Answer 2

higher reactivity = shifts towards products = exothermic reaction = K>0 = more negative ∆Gº = loss of free energy = more spontaneous

Question 3

What type of conjugate base does a strong acid produce?

Answer 3

weaker, more stable conjugate base, lower energy

Question 4

How are Ka and pKa related?

Answer 4

pKa = -logKa

Question 5

What is the acid association constant?

Answer 5

Ka=[H3O+][A-]/[HA] (in water solvent)

Question 6

What does a lower pKa mean?

Answer 6

=higher Ka = stronger acid = less reactive/weaker conjugate base

Question 7

What is an R-group? How does it related to pKa?

Answer 7

some substituent (of a functional group) that changes the pKa value

Question 8

How does protonation relate to pH?

Answer 8

acids are primarily in their protonated form when pH is less than their pKa

acids are in deprotonated form when pH is greater than pKa

Question 10

What are the 6 factors the effect the stability of the acid or conjugate base?

Answer 10

1. Electronegativity of Atom with negative charge
2. Size of Atom with negative charge
3. Resonance stabilization of negative charge
4. Inductive stabilization of negative charge
5. Orbital hybridization of atom with charge
6. Salvation of the conjugate base

Question 11

What is the relationship between K (equilibrium constant) and delta G (free energy)?

Answer 11

Larger K = stronger acid = more negative delta G = exothermic reaction = spontaneous reaction = weaker conjugate base = more stable/less reactive conjugate base

Question 12

How can acid/base strength be determined by electronegativity of an atom?

Answer 12

Weaker conjugate base = more stable = more stability if negative charge is on the more electronegative atom = more stable conjugate base = more acidic acid

Question 13

What are the steps to determine if a molecule is more acidic or basic?

Answer 13

Draw conjugate base of both molecules (remove H)

Question 14

When would you use size vs electronegativity to compare atoms to see which is more acidic or basic?

Answer 14

Same row: electronegativity
Same column: atom size

Question 15

How does size determine the acidity of an atom?

Answer 15

Larger size = charge spread over large volume/more diffuse = less reactive = weaker conjugate base = stronger acid

Question 16

How would you determine which acid is stronger if the two atoms are not in the same row or the same column

Answer 16

Ex. N and S:

N less acidic than O
O less acidic than S

So S is more acid than N

Question 17

What is the effect of resonance on acidity/basicity?

Answer 17

Resonance structure possibility = electron relocalized = negative charge is spread out across multiple atoms = negative charge stability = weaker conjugate base = stronger acid

Question 18

What happens if both atoms on a molecule can have delocalized?

Answer 18

Look at the atoms the electrons are delocalized from (ex C and O vs O and O = O and O is more stable = weaker conjugate base = stronger acid)

Question 19

What is the inductive effect on molecule acidity?

Answer 19

Polarization of electron density through a covalent bond by a nearby atom of higher electronegativity (through sigma framework)

Question 20

What is the effect of an electron-withdrawing group?

Answer 20

Stabilizes negative charge = weaker conjugate base = stronger acid

Make atom that has lone pairs more electronegative because the EWG is trying to pull the lone pair towards it through sigma (polar covalent) bond because the EWG itself is also electronegative

Question 21

Which atoms are more electron withdrawing than oxygen?

Answer 21

Halogens - creates a polar covalent bond

Question 22

What is the effect of distance of the EWG from the atom with the negative charge?

Answer 22

Shorter distance between EWG and atom with negative charge = more acidic = lower pKa

Question 23

How can you determine which halogen/EWG is better at stabilizing negative charge?

Answer 23

Electron with drawing ability is roughly based on electronegativity

We are NOT looking at halogen size because the halogen DOES NOT carry the negative charge

Question 24

How does the type of orbital affect the stability negative charge?

Answer 24

Closer electrons are held to nucleus = more stable

EFFECTIVE ELECTRONEGATIVITY

shorter the atomic orbital = closer to nucleus

Question 25

What are the relative orbital stabilities?

Answer 25

Sp > sp2 > sp3

Smallest to largest
Closest to farther from nucleus
Most stable to least conjugate base
Most acidic or least acidic

Question 26

How do you apply ARIO?

Answer 26

Importance/strength of effect is roughly in that order

Question 27

What is one exception where ARIO fails?

Answer 27

H-C- - - C - H

vs.

NH2(-)

Second has more electronegative N than C

BUT

The first has sp character second is sp3 character

First is more acidic

Question 28

How can you determine better base?

Answer 28

Lone pair must be more available = less stable base is better

A - less electronegative
R - no resonance structure/localized electron
I - no inductive effect