Addition of HBr to a double bond with an ether (-OR)...

Name: Problem 37, Chapter 10: Organic Chemistry
Uploaded: 2020-07-01T04:45:08-08:00
Duration: 2 min 2 s
Channel: Tom Rutherford
Description: Addition of HBr to a double bond with an ether (-OR) substituent occurs regiospecifically to give a product in which the -Br and -OR are bonded to the same carbon. Draw the two possible carbocation intermediates in this electrophilic addition reaction, and explain using resonance why the observed product is formed. (FIGURE CANNOT COPY)

Addition of HBr to a double bond with an ether (-OR) substituent occurs regiospecifically to give a product in which the -Br and -OR are bonded to the same carbon. Draw the two possible carbocation intermediates in this electrophilic addition reaction, and explain using resonance why the observed product is formed. (FIGURE CANNOT COPY)

Key Concepts

Regioselectivity in Electrophilic Addition

Regioselectivity refers to the preference for a chemical bond to form at one direction or position over another during a chemical reaction. In this case, because one of the potential carbocation intermediates is resonance-stabilized by the -OR group, the electrophilic addition proceeds in such a way that the halide (Br) ultimately bonds to the same carbon that holds the -OR. This outcome reflects the general tendency of the reaction to favor the formation of the more stable, resonance-stabilized intermediate.

Resonance Stabilization

Resonance involves the delocalization of electrons across adjacent atoms or groups. In the context of carbocations, an adjacent substituent like an ether (-OR) group can donate electron density through resonance, stabilizing the positive charge. This delocalization lowers the energy of that intermediate, making its formation more favorable relative to alternatives.

Electrophilic Addition Mechanism

This concept involves the initial attack of an electrophile (such as H?) on the double bond of an alkene, leading to the formation of a carbocation intermediate. The double bond acts as a nucleophile, and after the proton is added, a positively charged carbon species is formed, setting the stage for subsequent nucleophilic attack.

Carbocation Intermediate Formation and Stability

Carbocations are positively charged intermediates generated during electrophilic additions. Their stability is crucial in determining the reaction outcome. When multiple carbocation intermediates are possible, their relative stabilities—often influenced by neighboring groups—dictate which pathway is favored and consequently which final product is predominantly formed.

Transcript

Please give Ace some feedback