Organic Chemistry - Substitution/Elimination

Sn1 Substrate Hierarchy

3° > 2° > 1°

Sn2 Substrate Hierarchy

1° > 2° > 3°

Sn1 Requirement: Nucleophile

N/A - Irrelevant

Sn2 Requirement: Nucleophile

Strong Base

Sn1 Requirement: Leaving Group

Weak Base

Sn2 Requirement: Leaving Group

Weak Base

Sn1 Requirement: Solvent

Polar PROTIC

Sn2 Requirement: Solvent

Polar aPROTIC

Sn1 stereochemistry:

Racemic

Sn2 stereochemistry:

Inversion

E1 Stereochemistry:

N/A

E2 Stereochemistry:

Anti

E1 Substrate Hierarchy

Allylic > 3° > 2° > 1°

E2 Substrate Hierarchy

3° > 2° > 1°

E1 Nucleophile:

Weak Nuc/base

E2 Nucleophile:

Strong Base

E1 Leaving Group:

Weak Base

E2 Leaving Group:

Good Base

E1 Solvent

Polar PROTIC

E2 Solvent

Polar aPROTIC

Solvent: aprotic
Substrate: 3°
Base/Nuc: Good
Leaving Group: Good

E2
Base/Nuc & Leaving group are N/A

Solvent: aprotic
Substrate: 1°
Base/Nuc: Good Nuc/ Weak Base
Leaving Group: Good

Sn2

Solvent: aprotic
Substrate: 1°
Base/Nuc: Strong Base
Leaving Group: Good

Sn2

Solvent: aprotic
Substrate: 1°
Base/Nuc: Strong & Hindered
Leaving Group: Good

E2

Solvent: aprotic
Substrate: 2°
Base/Nuc: Good Nuc/ Weak Base
Leaving Group: Good

Sn2

Solvent: aprotic
Substrate: 2°
Base/Nuc: Strong
Leaving Group: Good

E2

Solvent: protic
Substrate: 1°
Base/Nuc: Strong Hindered Base
Leaving Group: Good

E2

Solvent: protic
Substrate: 1°
Base/Nuc: Strong Base
Leaving Group: Good

Sn2

Solvent: protic
Substrate: 1°
Base/Nuc: Good Nuc
Leaving Group: Good

Sn2

Solvent: protic
Substrate: 2°
Base/Nuc: Strong Base
Leaving Group: Good

E2

Solvent: protic
Substrate: 2°
Base/Nuc: Good Nuc/Weak Base
Leaving Group: Good

Sn2/Sn1

Solvent: protic
Substrate: 2°
Base/Nuc: Weak Nuc/Weak Base
Leaving Group: Good

Sn1/E1

Solvent: protic
Substrate: 3°
Base/Nuc: Strong Base
Leaving Group: Good

E2

Solvent: protic
Substrate: 3°
Base/Nuc: Weak Nuc/Weak Base
Leaving Group: Good

Sn1/E1

Solvent: protic
Substrate: 3°
Base/Nuc: Good Nuc/Weak Base
Leaving Group: Good

Sn1

Because E2 mechanism results in formation of a ___ bond, the two leaving groups (often a _____ and a ______) need to be ______ & _____

Because E2 mechanism results in formation of a _pi_ bond, the two leaving groups (often a _hydrogen_ and a _halogen_) need to be _anti_ & _coplanar_

The reaction rate of E2, influenced by both the alkyl halide and the base, is _____ order.

The reaction rate of E2, influenced by both the alkyl halide and the base, is _second_ order.

E1 Reactions mostly occurs in complete absence of ____ or presence of only a weak ____

E1 Reactions mostly occurs in complete absence of _base_ or presence of only a weak _base_

E1 reactions [do/do not] need the leaving groups to be anti & coplanar

E1 reactions _do not_ need the leaving groups to be anti & coplanar

the Sn2 reaction rate depends on the concentration of both the _______ and _______

the Sn2 reaction rate depends on the concentration of both the _substrate_ and _nucleophile_

Sn1 Rate Equation

r=k[substrate]

As steric hindrance around the electrophilic center increases, _______ is disfavored and _______ is the predominant reaction

As steric hindrance around the electrophilic center increases, _substitution_ is disfavored and _elimination_ is the predominant reaction

Stronger base favors [Sn2/E2]

Stronger base favors [E2]

Sn2 Rate Equation

r=k[substrate][nucleophile]

E1 Regiochemistry

Bulky Base: Hoffman
Non-bulky Base: Zaitsev

E2 Regiochemistry

Bulky Base: Hoffman
Non-bulky Base: Zaitsev