The Final Chapter 7 Ochem 1

Base Strength Trends

Down on Column = Weaker Base

Across Period = Weaker Base

More Resonance = Weaker Base

More negative charge = more basic

Resonance > Periodic Trends

When determining Base Strength

When Comparing 2 nucleophiles and determine strength)

Charge ( - > neutral)

When comparing on same period ( less electronegative >)

When comparing on same column ( larger >)

Bulkier = weaker nucleophile

More resonance = weaker nucleophile

Nucleophile Strength and Induction

More pulling = weaker nucleophile

Ethyl Alcohol

Protic Because OH Bond

Acetone

Aprotic

H- Exception

Weak Nucleophile

Sulfur Exception

Strong Nucleophile (even though its neutral) because of large electron clouds

Strong Nucleophile

Generally

Negatively Charged

Not Bulky

Generally Favors Substitution

Strong Base

Negatively Charged C,H,O, or N (*unless pi bonds are present)

Strong Nucleophile/Strong Base

Nucleophile is negatively charged C,O,or N with no pi bond or steric hinderance

Weak Nucleophile/ Strong Base

Nucleophile is

Negatively Charged C,O,or N but has steric Hinderance

Exception: H- is weak

Strong Nucleophile/ Weak Base

Nucleophile is

Negatively Charged

Either:

Not a C,H,O, or N

one of CHON but has nearby pi bonds

Exception: S is strong even though its neutral

weak nucleophile/ weak base

neutral nucleophile

SN2 and rate laws

r = k(ah)(n)

increasing solvent decreases AH and N by same factor cuz concentration

Increasing nucleophile increases AH and N by same factor

SN1 rate law

r = k (ah)

increasing solvent decreases AH and N by same factor cuz concentration dec

increasing nucleophile = no effect

Figure out reaction pathway WN/SB SN/SB SN/WB WN/WB

1 E2 Sn2 Sn2

2 E2 E2 Sn2 Sn1 &/or E1 ^

3 E2 E2 Sn1 &/or E1 ^ Sn1 &/or E1 ^

sn1 vs e1

heat favors e1

bully bases favor sn1

Zaitsev rule

when multiple h can be removed to form alkene, most substituted H is favored

Exception to Zaitsev Rule

least substituted h is favored when

f is leaving group

base is too bulky

most substituted h cant be removed due to antiperi planar requirement ( only applies to cyclic ringss undergoing E2 elimination)

SN1 Extra Info

Equal amount r and s ( draw the different stereoisomers for the carbon involved)

E1 Extra info

Zaitsev rule

sn2 extra info

inverted

e2 extra info

Zaitsev rule

anti peri planar required

sn2 electrophile reactivity

Methyl>1>2>3 (matter most )

benzyllic>allylic>normal sub

sn1/e1/e2 electrophile reactivity

3>2>1 methyl

substitution

leaving grouple is replaced by nucleophile

elimination

leaving group and beta hydrogen removed to form double bond

aprotic

no h bond donor

best for Sn2/E2

Smaller Nu- is better

protic

H-Bond donor

Best for Sn1/E1

Larger Nu- are better

counterclockwise rotation

S

clockwise rotation

R

Most Reactive =

Weakest Base

What matters when it comes to reactivity

substitutitutioon first than base strength

sn1/e1/e2 electrophyle reactivity

3>2>1>methyl (matters most)

normal>allylic>benzyllic