Zusammenfassung der Ressource
13.3 & 13.4 Reactions of Alkenes and
Electrophillic Addition
- Addition reactions of the alkenes
- Hydrogen Halides
- Alkenes react with gaseous hydrogen halides at room temp to form haloalkanes
- If alkene is gaseous, reaction take place when two gases are mixed
- If alkene is liquid, the the hydrogen halide is bubbled through it
- Alkenes can also react with concentrated HCl or HBr (which are solution of the hydrogen halides in water)
- Each of these reactions involves the ADDITION of a small
molecule across the double bond, causing the pi bond to
break, and new bonds to form
- Hydrogenation of Alkenes
- Nickel Catalyst
- 423K
- Alkene + Hydrogen = Alkane
- Hydrogenation of Propene >>
- Hydration reactions of Alkenes
- Alkene + Water (steam) --> Alcohol
- Requires the presence of a phosphoric acid catalyst (H3PO4)
- Can form a Primary or secondary alcohol
- Halogenation
- Rapid addition reaction with the halogens: Cl or Br at room temperature
- Haloalkane
- Electrophilic addition in Alkenes
- Alkenes usually take part in addition reactions to form saturated compounds = ELECTROPHILLIC ADDITION
- Double bond in an alkene represents region
of high electron density due ton presence of
pi-electrons
- High electron density attracts electrophiles
- Electrophile = An atom that is attracted to an electron-rich
centre and accepts an electron pair. Usually a positive ion or
molecule containing an atom with a partial positive charge.
- ^^ The mechanism
- Markownikoff's
Rule
- You can have a primary or secondary carbocation. This is similar to a primary or secondary alcohol.
- Carbocation Stability
- The stability increases as you go from primary carbocation, through to tertiary carbocation.