e1&2, sn1&2

Flashcards covering key concepts, definitions, and memorization tips related to nucleophilic substitution and elimination mechanisms.

SN2

Substitution, Nucleophilic, Bimolecular; a one-step mechanism involving backside attack with inversion of stereochemistry.

Stereochemistry for SN2

Inversion of configuration during the reaction.

Substrate preference for SN2

Methyl > 1° > 2° (never 3°) substrates preferred.

Nucleophile for SN2

Strong and small nucleophiles such as -OH, -OR, -CN, or -N.

Solvent for SN2

Polar aprotic solvents like DMSO, DMF, or acetone.

Rate for SN2

Rate is determined by k[substrate][nucleophile].

Key notes for SN2

No carbocation formation; steric hindrance prevents SN2 reactions.

Fast phrase for SN2

Primary + strong nuc → SN2.

SN1

Substitution, Nucleophilic, Unimolecular; a two-step mechanism with carbocation formation.

Stereochemistry for SN1

Racemization occurs during the reaction.

Substrate preference for SN1

3° > 2° substrates preferred (never 1°).

Nucleophile for SN1

Weak nucleophiles such as H2O or ROH.

Solvent for SN1

Polar protic solvents like H2O or ROH.

Rate for SN1

Rate depends on k[substrate].

Key notes for SN1

Possible rearrangements may occur.

Fast phrase for SN1

Tertiary + weak nuc → SN1.

E2

Elimination, Bimolecular; a one-step mechanism requiring a strong base.

Base for E2

Strong bases such as -OH, -OR, or tBuO-.

Substrate for E2

2° or 3° substrates preferred.

Geometry for E2

Anti-periplanar geometry of hydrogen is required.

Rate for E2

Rate is determined by k[substrate][base].

Key notes for E2

Heat favors elimination and Zaitsev's rule applies unless a bulky base is used.

Fast phrase for E2

Strong base = E2.

E1

Elimination, Unimolecular; a two-step mechanism with carbocation formation.

Base for E1

Weak bases such as H2O or ROH.

Substrate for E1

Prefer 3° or 2° substrates.

Solvent for E1

Polar protic solvents are used.

Key notes for E1

Possible rearrangements and often paired with SN1.

Fast phrase for E1

Tertiary + weak base + heat → E1.

Quick Decision Table

Primary + strong nucleophile → SN2; Tertiary + weak nuc/base → SN1/E1; Tertiary + strong base → E2; Secondary + strong nuc → SN2/E2 mix. Heat favors elimination.

Memory Tips

Strong = SN2/E2, Weak = SN1/E1, Primary favors SN2, Tertiary favors SN1/E1 or E2, Heat favors elimination.