electrophilic addition of hydrogen halide to alkenes

hydrogen halide molecules have…

a permanent dipole as halogen atoms are more electronegative than hydrogen (hydrogen atom is delta positive)

mechanism for electrophilic addition

• the positive hydrogen on the hydrogen halide is attracted to the high electron density of the double bond

• the positive charge on the hydrogen atom attracts the pair of electrons in the pi bond of the alkene

• these move towards the hydrogen atom

• hydrogen atom can only have one covalent bond - at the same time, the pair of electrons in the covalent bond between the hydrogen and the halide move onto the halide

• this is heterolytic fission

• 2 products - positively charged carbocation intermediate with a positively charged carbon atom

• negatively charged halide ion

• the electron pair on the halide ion are attracted to the positive carbon - forms covalent bond

• product formed

what is an electrophile

a positive ion or molecule attracted to regions of high electron density

what is heterolytic fission

the uneven breaking of a covalent bond where one bonding atom retains both shared electrons