Chapter 10: Substitution and Elimination Reactions

A set of flashcards covering key concepts, definitions, and mechanisms related to substitution and elimination reactions in organic chemistry.

What distinguishes substitution reactions from elimination reactions?

Substitution replaces a leaving group with a nucleophile, while elimination removes a leaving group and an adjacent hydrogen to form an alkene.

What are leaving groups?

Groups that are stable as anions and can be replaced in substitution reactions.

What are the two types of mechanisms for substitution reactions?

Bimolecular (SN2) and unimolecular (SN1).

In SN2 reactions, who is involved in the rate-determining step (RDS)?

Both the nucleophile and the electrophile.

What is a key characteristic of the nucleophile in SN2 reactions?

It performs a backside attack that inverts any stereochemistry.

What is the order of reactivity for substrates in SN2 reactions?

Methyl > primary > secondary > tertiary.

How does nucleophilicity relate to basicity?

Nucleophilicity is similar to basicity when considering the same atom.

Name a strong nucleophile in comparison with water.

OH- is better than H2O.

What makes a good leaving group?

A good leaving group must be stable after removal, with properties influenced by factors such as resonance and electronegativity.

Why is OH- considered a poor leaving group?

Because it's a strong base and unstable as an anion.

What type of solvent slows down SN2 reactions?

Polar protic solvents, such as water or ethanol.

What solvent type speeds up SN2 reactions?

Polar aprotic solvents, like acetonitrile or DMF.

How does Zaitsev's rule relate to elimination reactions?

Zaitsev's rule states that the more substituted alkene is typically the major product of elimination reactions.

What is the difference between E2 and E1 elimination reactions?

E2 is bimolecular with both base and electrophile in the RDS, while E1 is unimolecular with only the electrophile in the RDS.

What is the importance of the anti-periplanar relationship in E2 reactions?

E2 elimination reactions require that the hydrogen being removed is antiperiplanar to the leaving group.

What influences whether a nucleophile will act as a base in reactions?

The presence of the leaving group and the competing nucleophilic and basic properties.

What are anti-Zaitsev or Hofmann products?

Alkenes that are formed preferentially when using sterically bulky bases.

How do polar protic solvents impact SN1 reactions?

They stabilize suitable carbocations and slow down nucleophile interactions.

What happens to stereochemistry during SN1 reactions?

The initial stereochemistry is destroyed due to the formation of a carbocation intermediate.

What type of reactions can weak bases be associated with?

Both substitution and elimination reactions, depending on the context.

Which substrate would favor SN2 reaction over E2?

Methyl substrates favor SN2 reactions.

What is the main characteristic of E1 reactions regarding temperature?

E1 reactions are favored at higher temperatures.

What is the significance of ΔG = ΔH – TΔS in substitution and elimination reactions?

It represents the Gibbs free energy change, which can influence whether substitution or elimination is favored.

What role does steric hindrance play in substitution and elimination reactions?

Steric hindrance affects the reactivity of substrates; more hindered substrates favor elimination processes.

What example demonstrates that leaving groups can be cationic intermediates?

A protonated oxonium leaving group during E1 reactions.

How does nucleophile strength vary with size?

Larger atoms tend to be better nucleophiles but poorer bases due to the ease of bond formation.

How can the stability of a leaving group be measured?

Based on its resonance, electronegativity, and size.

What is the impact of the solvent type on nucleophile reactivity?

The solvent can either stabilize the nucleophile or enhance its reactivity depending on whether it's protic or aprotic.