DAT ORGO - Substitution and elimination

Substitution reactions - general formula

elimination reactions - general formula

What is the most common leaving group and what is the trend?

halogens, the bigger the size, the better the leaving group

Other good leaving groups other than halogens

TsO TfO, MsO

What cant Leaving groups be attached to?

SP2 hybridized carbons

Sn1 reaction

Heat is the rate determining step!

Forms a racemic mix of the two enantiomers

Whats the rate law for Sn1 reactions

it looks like rate=k(electrophile)

What will make something more reactive towards an Sn1 reaction

increasing carbocation stability

What strength electrophile do SN1 reactions need

a weak one, because strong ones will just do it themselves instead of waiting for heat

Can SN1 reactions undergo rearangements

yes, due to carbocation intermediate

SN2 reaction

What are the kinetics of an SN2 reaction

The rate determining step is the first one, following second rate kinetics, dependent on both the electrophile and the nucleophile

SN2 reactivity trend

The more substituted the leaving group, the more likely it is not to happen

SN2 stereoselectivity

the nucleophile will always attack opposite to the leaving group

What happen in an SN2 reaction for a split second

The molecule is sp2 hybridized

What strength does the nucleophile need to be for an SN2 reaction

Strong

What happens to the stereochemistry in an SN2 reaction

It inverts

How to choose between SN1 and SN2 reactions

1. what the leaving group is attached to, if its attached to a 3 prime carbon, it is SN1 if it is attached to a 1’ carbon, its SN2, if 2’, it could be either

2. Strong nucleophile (SN2) (metals with NOF), weak nucleophile (SN1)(no metal or resonance stabilization)

E1 reactions

much like SN2, heat is the rate determining step

E1 carbocation stability

Increasing carbocation stability leads to increasing E1 reactivity

Zatsiev rule

E1 and E2 reactions favor the more substituted C=C bond

E2 reactions

E2 Kinetics

Rate=K(electrophile)(base)

E2 stability

More substitued, more reactions

due to zatsiev’s rule

What alkenes are favored during E reactions

E alkenes

How to choose between E1 or E2

primary- E2

All the rest - E1 or E2

Strong base - E2 , Weak base E1

What happens if your nucleophile /base is weak?

then it is a weak reaction

Base size when determining SN1, SN2, E1 and E2

larger nucleophiles/bases act more as bases as they are too large

smaller nucleophiles/bases act more as nucleophiles as they can fit

What counts as a “large” nucleophile/base

anything bigger than ethanol

What counts as a “small” nucleophile/base

Negativley charged carbon and sulfur

acetate

protic solvents

solvents with H atoms bonded to oxygen, nitrogen, or sulfur NOS

What do protic solvents do

they stifle strong nucleophiles/bases, which is good for SN1/E1, E2 does ok though

What Happens when an Sn2 nucleophile is paired with its conjugate acid

it still undergoes SN2

What happens if you have a halide nucleophile

protic/aprotic solvents will have a strong factor in whether or not it is a SN1/SN2

Protic - SN1

Aprotic - SN2

Zaitsev exception 1

Conjugated dienes will always be more favorable

Zatsiev exception 2

Tert butyls will favor the less subtituted C=C bond

Why are z products sometimes favored in SN2 reaction

Due to preset stereochemistry and the fact that the hydrogen and LG need to be opposite

CYCLOHEXANE AS WELL

What does more negative charge mean

more nucleophilicity

What does more resonance mean

less nucleophilicity

What trend on the periodic table is nucleophilicity

less electronegative = less able to handle a negative charge, hence increasing nucleophillicity

in protic solvents, how does nucleophilicity increase

down a column

in aprotic solvents, how does nucleophilicity increase

up a column

Which trend wins?

in aprotic: left to right

in protic: top to bottom

neutral halogens trend

really weak nucleophiles