Organic Chemistry Exam 3 Flashcards

NaOH (Base? Nucleophile? Hindrance?)

SB, SN, Unhindered

H2O (Base? Nucleophile? Hindrance?)

WB, WN, Unhindered

CH3OH, methanol (Base? Nucleophile? Hindrance?)

WB, WN, Unhindered

CH3CH2OH, ethanol (Base? Nucleophile? Hindrance?)

WB, WN, Unhindered

CH3CH2OH, ethanol (Base? Nucleophile? Hindrance?)

WB, WN, Unhindered

NaH (Base? Nucleophile? Hindrance?)

SB, SN, Unhindered

NaNH2 (Base? Nucleophile? Hindrance?)

SB, SN, Unhindered

NH3, ammonia (Base? Nucleophile? Hindrance?)

SB, SN, Unhindered

NaSH (Base? Nucleophile? Hindrance?)

WB, SN, Unhindered

(CH3)3COH, t-butanol (Base? Nucleophile? Hindrance?)

WB, WN, Hindered

(CH3)3COK, t-butoxide (Base? Nucleophile? Hindrance?)

SB, WN, Hindered

LDA, LiN(i-Pr)2, Lithium Diisopropyl Amide (Base? Nucleophile? Hindrance?)

SB, WN, Hindered

CH3CO2Na, acetate (Base? Nucleophile? Hindrance?)

WB, SN, Unhindered

CH3CO2H, acetic acid (Base? Nucleophile? Hindrance?)

WB, WN, Unhindered

KCN (Base? Nucleophile? Hindrance?)

WB, SN, Unhindered

What kind of reaction would a methyl L.G. undergo?

S_N2

What kind of reaction would a primary L.G. undergo?

S_N2 / E2

What kind of reaction would a secondary L.G. undergo?

S_N2 / E2, minor S_N1 / E1

What kind of reaction would a tertiary L.G. undergo?

S_N1 / E1 or E2

Primary, SB, WN, Unhindered gives what reaction?

S_N2

Primary, SB, WN, Hindered gives what reaction?

E2

Primary, SN, gives what reaction?

Sn2

Secondary, SN, WB, gives what reaction?

S_N2

Secondary, SB, Unhindered gives what reaction?

E2, Saytzeff major

Secondary, SB, Hindered gives what reaction?

E2, Hoffmann major

Tertiary, WB, WN, Low temp gives what reaction?

S_N1

Tertiary, WB, WN, High temp gives what reaction?

E1, Saytzeff major

Tertiary, SB, Unhindered gives what reaction?

E2, Saytzeff major

Tertiary, SB, Hindered gives what reaction?

E2, Hoffmann major

What makes a good leaving group?

• Weakly Basic

• Stable

Saytszeff Product will be the major product when using a(n) ______ base

Unhindered

Hoffmann Product will be the major product when using a(n) ______ base

Hindered

Hindered bases attack protons attached to ____ substituted carbons

Less

Unhindered bases attack protons attached to ____ substituted carbons

More

For E2 reactions, the leaving group and the proton being removed must be ___________

anti-coplanar / anti-periplanar

Carbocations from most to least stable

1. Tertiary

2. Secondary

3. Primary

4. Methyl

When will a hydride shift occur?

When a secondary carbocation is adjacent to a tertiary carbon

When will a methyl shift occur?

When a secondary carbocation is adjacent to a quaternary carbon

Hyperconjugation

Occurs when a sp³ hybridized orbital of a neighboring carbon overlaps with an unhybridized p-orbital of the carbocation

Hybridization of carbocations

sp²

Why do S_N1 and E1 reactions result in a racemic mixture?

The hybridization of carbocations (sp²) allows the nucleophile to attack from either side

Racemic mixture

The same amount of both stereoisomers

When does ring expansion occur?

When a carbocation is adjacent to a cyclopropane or cyclobutane

Rate determining step of S_N1 and E1 reactions?

Carbocation formation

What increases the rate of S_N1 Reactions?

• High temperature

• Concentration of substrate

• Polar protic solvent

What increases the rate of S_N2 Reactions?

• High temperature

• Concentration of substrate

• Concentration of nucleophile/base

• Polar aprotic solvent

What increases the rate of E1 reactions?

• High temperature

• Concentration of substrate

• Polar protic solvent

What increases the rate of E2 reactions?

• High temperature

• Concentration of substrate

• Concentration of nucleophile/base

• Polar aprotic solvent

What are the two leaving groups we use in this class besides the halogens?

Water and Sulfonyl groups

The Acid-Catalyzed Dehydration Reaction comprised of what two mechanisms?

Acid/Base Reaction + E2/E1 Mechanism

How to recognize an Acid-Catalyzed Dehydration Reaction

Alcohol + Acid + Heat (>100°C) = Alkene

Steps of an Acid-Catalyzed Dehydration Reaction

1. Convert the alcohol into water using one of the hydrogens from the acid (acid-base reaction)

2. Leaving group leaves (carbocation formation

3. The acid takes a hydrogen from one of the carbons adjacent to the carbocation, then the lone pair forms a double bond between the carbocation and the carbon

What elimination mechanism comes after the acid-base reaction in an Acid-Catalyzed Dehydration reaction? (1° alcohol)

E2

What elimination mechanism comes after the acid-base reaction in an Acid-Catalyzed Dehydration reaction? (2° & 3° alcohols)

E1

__________ reactions take place in 1 step and have no intermediates

Concerted (S_N2 and E2)

Endergonic steps/reactions have the intermediate/product at a _______ energy than the reactants

Higher

Exergonic steps/reactions have the intermediate/product at a _______ energy than the reactants

Lower

Hammond-Leffler Postulate

Exergonic steps have transition state structures similar to the “starting” structure for that step, and endergonic steps have transition state structures similar to the “final” step’s structure

Steps of an S_N2 Reaction

1. Lone pair of nucleophile attacks carbon with the leaving group, and leaving group leaves.

   • Inversion of configuration

Steps of an E2 Reaction

1. Lone pair of base attacks a hydrogen of a carbon adjacent to the carbon attached to the leaving group, and alkene forms between the carbons, and the leaving group leaves

Steps of an S_N1 Reaction

1. Carbocation formation (Leaving group leaves)

2. Nucleophile attacks carbocation

3. Acid-base reaction (Leaving group takes nucleophile’s hydrogen)

Steps of an E1 Reaction

1. Carbocation formation (Leaving group leaves)

2. Base takes a hydrogen from a carbon adjacent to the carbon that had the leaving group

   • Alkene forms

Addition reactions

Add X and Y across a double bond

Hydrogenation reaction

Adding H₂ across an alkene using a catalyst and pressure

Effective catalysts for hydrogenation reactions

Metal catalysts in the solid phase

Examples of effective catalysts for hydrogenation reactions

Ni, Rh, Pd, and Pt

Heterogenous catalysts

Do not dissolve in solvent

Syn addition

Things that are added to a double bond are added to the same side of that double bond

Key features of hydrogenation reactions

• Presence of Alkene

• H₂

• Catalyst

• Pressure

Stereospecificity

The product of a syn/anti reaction are a specific type of stereoisomer