SN1, SN2, E1, E2

SN1

polar solvent, HX nucleophile

SN1

tertiary halogenoalkanes react in this method; first the halogen breaks off then the nucleophile attaches onto the positively charged carbon

SN1

The mechanism that forms a carbocation in the rate-determining step is the _____ mechanism.

SN1

addition of an acid, carbo-cation formation, addition of nucleophile

SN1

reaction type that needs highly substituted substrate and any nucleophile

SN1

Involves two steps. Step 1: The dissociation of a molecule into a carbocation and a good leaving group. Step 2: Combination of the carbocation with a strong nucleophile. The slowest step is the formation of the carbocation. Structural factors and solvent effects may accelerate the formation of the carbocation. Result is a loss of optical activity. First order kinetics; K=[A].

SN2

CH3X>primary>secondary, 1 step, nucleophile attachs as good LG leaves

SN2

Primary halogenoalkanes follow the _______ mechanism of nucleophilic substitution.

SN2

secondary halide + weakly basic nucleophile + polar aprotic solvent

SN2

The mechanism that forms a transition state with a high activation energy is the _____ mechanism.

SN2

1 step has no carbo-cation

E1

reaction type that needs a highly substituted substrate and any base

E1

2 steps, good LG leaves, electron is moved to form double bond

E1

Two step process proceeding through a carbocation intermediate. Rate of reaction dependent on substrate. Elimination of a leaving group and a proton results in the production of a double bond. Step1: Leaving group departs, producing a carbocation. Step 2: Proton is removed by a base.

E1

least likely mechanism out of sn1, sn2, e1, e2

E2

A one-step elimination reaction

E2

Primary halide + strong base +aprotic solvent

E2

reaction type that needs a strong base

E2

Occurs in one step. A strong base removes a proton, while a halide ion anti to the proton leaves. Steric hinderance does not greatly affect these reactions.

E2

bimolecular elimination, strong base remove proton, halide anti to proton leaves and makes db

What are the types of reactions on Test 2?

SN1, SN2, E1, E2

What is an alkyl halide?

Which reactions can an alkyl halide undergo?

SN1, SN2, E1, E2

What is an SN1 reaction?

An SN1 reaction proceeds by way of a mechanism in which the leaving group dissociates in a kinetically slow step, producing a planar carbocation which is then rapidly attacked by a nucleophile.

Steric congestion tends to promote SN1-type mechanisms, so a tertiary alkyl halide, like t-butyl chloride, would favor pushing the leaving group off to form the carbocation.

What is an SN2 reaction?

In this mechanism, one bond is broken and one bond is formed synchronously, ie. in one step.

SN2 is a kind of nucleophilic substitution reaction mechanism.

What is an E1 reaction?

What is an E2 reaction?

SN1 vs SN2

SN1 vs SN2

Mechanism diagram:

E1 vs E2

E1 vs E2

Mechanism comparisons:

SN1 vs E1

SN2 vs E2

SN2 vs E2 rates

SN1 vs SN2: The nucleophile

SN2 requires a strong nucleophile, while nucleophilic strength doesn't affect SN1.

SN1 vs SN2: Solvents

SN1 vs. SN2 reactions

E2 vs. E1 reactions

What is the rate of the reaction dependent on for SN2 reactions?

Concentration of the alkyl halides AND the nucleophile

In SN2 reactions, the rate of the reaction with a given nucleophile ____ with INCREASING size of the alkyl halides

decreases

In SN2 reactions, the configuration of the substituted product is ____

compared to the starting material

inverted

What does the rate of the reaction depend on for SN1 reactions?

ONLY on the concentration of the alkyl halide

In SN1 reactions, the rate of the reaction is favored by..

- the bulkiness of the alkyl substituent

- the bulkier the better

In SN1 reactions, in the substitution of a chiral alkyl halide, a ___________ of product is obtained

racemic mixture

How do you determine whether or not you have a substitution or elimination reaction?

1. Look at reagent

2. Look at substrate

3. Determine mechanism

4. Consider stereochemistry, rearrangements and stability of potential products when applicable.

SN2/E2 reactions are favored by?

- HIGH concentration of nucleophile

- STRONG base

Favored by a HIGH concentration of nucleophile and a STRONG base

SN2/E2 reactions

SN1/E1 reactions are favored by?

POOR nucleophile

WEAK base

Favored by a POOR nucleophile and WEAK base

SN1/E1 reactions

SN2 vs. E2

SN1 vs. E1

- Slows SN2

- Helps E2

Steric effects

Helps SN2 but helps E2 MORE

Basicity

- Kinetic idea; Polarizability

- Helps SN2

- Helps SN1 2nd step

Nucleophilicity

Charge of leaving group?

Leave NEUTRAL if possible

Charge of attacking group?

NEGATIVE if possible

Helps E2 and E1

High base concentration

Helps SN2 only

solvent

All reactions increase but E2 > SN2

Temperature

If good enough, SN1 or E1

Stability of possible carbocations

What type of reaction does an ethoxide ion favor?

Steric hindrance at alpha and beta carbons produce what effect on SN2/E2 when tertiary or secondary?

- SN2 is slowed

- E2 becomes FASTER

When is substitution favored?

Given that the major reaction of a secondary alkyl halide with an alkoxide ion is elimination by the E2 mechanism, we can expect the proportion of substitution to increase with?

1) decreased crowding at the carbon that bears the leaving group

2) decreased basicity of the nucleophile

What does primary mean?

Attached to one thing

What does secondary mean?

Attached to 2 things

What does tertiary mean?

Attached to 3 things

Strong base

Weak nucleophile

E2

*primary, secondary or tertiary does not matter

Strong base

Strong nucleophile

*Primary

SN2

Strong base

Strong nucleophile

*Secondary

E2

Strong base

Strong nucleophile

*Tertiary

E2

Weak base

Strong nucleophile

*Primary

SN2

Weak base

Strong nucleophile

*Secondary

SN2

Weak base

Strong nucleophile

*Tertiary

SN1

Weak base

Weak nucleophile

*Primary

No reaction

Weak base

Weak nucleophile

*Secondary

SN1/E1

*only when solvolysis occurs at secondary

Weak base

Weak nucleophile

*Tertiary

SN1 and E1

NaH, DBN, DBU

Strong base

Weak nucleophile

HO-, MeO-, EtO-

Strong base

Strong nucleophile

Halides: I-, Br-, Cl-

Sulfur groups: RS-, SH-, RSH, H2S

Weak base

STRONG nucleophile

H2O, MeOH, EtOH, Alcohols (R-OH)

Weak base

Weak nucleophile

What is an alcohol?

What are the strong nucleophiles?

What are the weak nucleophiles?

What are the strong bases?

Determine the reagent:

NaH

SB, WN

Determine the reagent:

DBN

SB, WN

Determine the reagent:

DBU

SB, WN

Determine the reagent:

HO-

SB, SN

Determine the reagent:

MeO-

SB, SN

Determine the reagent:

EtO-

SB, SN

Determine the reagent:

I-

WB, SN

Determine the reagent:

Br-

WB, SN

Determine the reagent:

Cl-

WB, SN

Determine the reagent:

RS-

WB, SN

Determine the reagent:

HS-

WB, SN

Determine the reagent:

RSH

WB, SN

Determine the reagent:

H2S

WB, SN

Determine the reagent:

H2O

WB, WN