intro to addition reactions

Electrophilic Addition Mechanism

• Involves breaking double bonds (alkenes) and adding halogens (Br, Cl, I).

• Key reaction structures involve bromonium ions as intermediates.

Stereochemical Implications

• Addition of bromine to cyclopentene produces only trans-dibromocyclopentane.

• Cannot have both bromines on the same carbon (one wedge, one dash is impossible).

• There are measurable intermediates like the bromonium ion in electrophilic addition.

Reaction Mechanism and Intermediates

• Mechanism involves formation of carbocation from double bond attack by bromine.

• Reaction resembles SN1 in that it forms a positively charged bromonium ion.

• In nucleophilic solvents (e.g., water, methanol), nucleophiles like water can now react with the intermediate.

Solvent Effects on Reaction Pathway

• Solvent presence affects likelihood of reaction outcomes.

• In nucleophilic solvents, the nucleophile from the solvent is more likely to react with the carbocation than Br- ion produced.

Chirality and Products

• Analyzing products for chirality: determines how many enantiomers are produced.

• Important to understand if only one or multiple chiral centers exist in products.

• SN1 and SN2 characteristics need to be identified in exam questions for accurate drawings and structures.

Summary of Mechanism Steps

1. Attack by bromine to form a bromonium ion.

2. Reaction of nucleophile (solvent molecule) leads to the final product.

3. Distinguish between two-step and one-step reactions (SN1 vs SN2 methods).