Alkyl Halides and Nucleophilic Substitution

A set of flashcards covering key concepts from the lecture on alkyl halides and nucleophilic substitution, including mechanisms, evidence, and factors influencing reaction rates.

What role does -OH play in nucleophilic substitution reactions involving alkyl halides?

-OH acts as a nucleophile since it forms a bond with carbon, not hydrogen.

What is the role of CH3-Cl in nucleophilic substitution?

CH3-Cl acts as an electrophile, donating carbon, not as a proton donor.

What are the two mechanisms possible for nucleophilic substitution reactions of alkyl halides?

The two mechanisms are Nucleophilic Substitution Bimolecular (SN2) and Nucleophilic Substitution Unimolecular (SN1).

How does the nucleophile approach carbon in an SN2 reaction?

In an SN2 reaction, the nucleophile makes a 'back side attack' on carbon.

What type of evidence supports the SN2 mechanism?

Stereochemical evidence and kinetic evidence support the SN2 mechanism.

What are the factors affecting the rate of SN2 reactions?

The structure of alkyl halide, the leaving group, and the solvent are factors affecting the rate of SN2 reactions.

How does the leaving group affect the rate of SN2 reactions?

The best leaving groups are the weakest bases; the order of decreasing base strength is I- > Br- > Cl- > F-.

What type of solvent is preferred for faster SN2 reactions and why?

Polar aprotic solvents are preferred because they do not form hydrogen bonds with nucleophiles, allowing for greater reactivity.

What occurs during the first step of the SN1 mechanism?

In the first step of the SN1 mechanism, a carbocation is formed through the heterolytic cleavage of the C-X bond.

What is the rate-determining step in an SN1 reaction?

The rate-determining step is the formation of the carbocation, which is slower than the subsequent step where the nucleophile attacks.

How does the structure of alkyl halides affect the SN1 reaction rates?

Alkyl halides that form more stable carbocations will react faster; the order of stability is 3° > 2° > 1° > methyl.

What evidence supports the SN1 mechanism?

Evidence includes findings of both inversion and retention products in 50% yields.

How do the nucleophiles in SN1 reactions differ from those in SN2 reactions?

SN1 reactions can proceed with weaker nucleophiles, often in the presence of protic solvents.

What is observed about carbocations during the SN1 mechanism?

Carbocations have varying stabilities, with tertiary being the most stable and reactive.

What is a characteristic feature of nucleophiles in protic solvents during SN2 reactions?

Larger nucleophiles are typically more reactive due to weaker hydrogen bonds with solvent molecules.