E n alkenes react as nucleophiles andor bases in

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E N Alkenes react as nucleophiles and/or bases in electrophilic addition reactions In general, electrophilic addition to the double bond is a two-step process: Second, the resulting carbocation reacts with a nucleophile. First, the π bond reacts with an electrophile. (Other mechanisms are also possible (later))
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7 Your First Reaction: Addition of HBr to an Alkene an electrophilic addition reaction 1st Step: Addition of a proton to the alkene. The proton is the electrophile. 2nd Step: Bromide traps the carbocation. Bromide is the nucleophile. Electrophilic Addition Reaction of an alkene with identical substituents on the two carbons leads to one product. H B r H B r cyclopentene bromocyclopentane
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8 Electrophilic Addition If the alkene carbons have different substituents, two regioisomeric products are possible. H B r B r H + H B r 1 - b r o m o - 1 - m e t h y l - c y c l o p e n t a n e 1 - b r o m o m e t h y l - c y c l o p e n t a n e A B major minor Electrophilic Addition: Markovnikov’s Rule The regioselectivity of this reaction was first observed by Markovnikov in 1869. (unknown in the West until 1899) He found that in a Brønsted acid, the hydrogen, which is the electrophile , adds to the carbon that contains the larger number of hydrogens .
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