3.3.4.2 Addition reactions of alkenes

Electrophilic addition reaction occurs if a double bond is present See card

Markovnikov’s rule: 99% of the time: the hydrogen becomes attached to the carbon with the most hydrogens already attached to it This is because it produces a more stable cation The alkyl groups donate electron density (inductive effect)

X (halogen) is more electronegative than the hydrogen Bonding pair of electrons is attracted to the X Hydrogen becomes slightly positively charged The slightly positive hydrogen is the electrophile, and is attracted to the pi bond Pi bond breaks and the electron pair swings down to form a bond with the hydrogen atom At the same time, the electrons in the H-X bond are repelled right down on to the X to give an X- ion Electrons can swing left or right to produce two different products More likely to swing right because it is a quicker process and more stable

See card

Electrophilic addition See card

See card Step 1: Arrow 1 = from double carbon bond to hydrogen atom Arrow 2 = from H - Halogen bond to halogen atom Step 2: Arrow = from bromide ion to positively charged carbon atom Forms a halogenoalkane

Electron deficient atom or ion Attacks areas of high electron density

Electrophilic addition

HOSO3H

A more stable cation is produced due to the inductive effect