Orgo Exam 2

a __ PKa is associated with a _ acid

a lower PKa is associated with a stronger acid

Stronger acid = ___ CB 

Stronger acid = weaker CB 

More stable base = __ base

More stable base = weaker base

Why does stabilizing a molecule = weaker base?

Stabilizing a molecule lowers the energy of the electrons and they’re less available to donate.

Resonance does what to bases?

Resonance stabilizes bases

• More stable base; weaker base

Induction does what to bases?

EN atoms pull e- density away from a base which becomes less negative 

• Less negative = worse base

• ex: F is EWG and stabilizes the negative charge

Explain why less negative = worse base

because (+) charge lowers the energy of the e-s and they are less available to donate

What does induction have to do with bases?

sp = most stable

• More stable = weaker base

What side of the equation does equilibrium favor in an acid-base reaction?

Eq. favors the higher PKa

• Reaction always proceeds from strong to weak acid 

What’s the key to memorizing how to compare bases:

Atom

Resonance
Induction
Orbitals 

What’s the atom rule for comparing base strength? 

• Same period = EN trends 

• Same group = Size trends 

Rate laws for all mechanisms?

SN2: rate = K[Nu][E]

E2: rate = K[B][E]

units are M*s^-1

SN1: rate = K[E]

E1: k[E]

What are the common weak Nu? 

3

Given H₂SO₄  or H₃PO₄ as the solvent what mechanism will occur?

E1

Heat promotes what 

E1 over SN1

1* alcohols with HCl, HBr, or HI lead to what mech

SN2

Draw the RCD for E1, SN1, E2, SN2

Zaitsev Rule

more stable = more substituted

When is Hoffman’s Rule favored?

(never for E1) when a bulky base is used

Thee pKa of H₃O⁺ is -1.7 and given that HN₃ :  H₃O⁺ is 10⁵ : 1, what is the pKa of HN₃? 

3.3 because every multiple of 10 is equal to 1.0 pKa. 

-1.7 + 5 =3.3 

A better leaving group is what? 

Bigger, more polarizable 

Cyclopropane is more acidic than cyclohexane, why? Consider s character and bond angles 

The C-C-C bond angles of cyclopropane is 120 and the cyclohexane is 109. 120 has more S character and better able to stabilize electrons  

Given this NU/Base what does the M stand for?

MCN

M = counter cation

Why is a five carbon ring better than a four

because there is less ring strain

When is Hoffman favored

during E2 when we use a statically hindering base

Write the four things for bases/nu

Nucleophile def

gives up/donates e-

electrophile 

poor in e- density, has fewer electrons, wants electrons 

What makes a good leaving group

• weak base

• More negative pKa better

• stable

Big bulky, sterically hindered, bases

LDA, t-BuOK

Substitution vs. Elimination

Substitution:

• Nu replaces LG

Elimination:

• Double bond is formed

• Beta hydrogens

Better LG is what

bigger atom, more polarizable