3.4 Alkenes Flashcards
what are alkenes ?
- unsaturated hydrocarbons with general formula CnH2n
why are alkenes vulnerable to attacks from species?
- they contain a high electron density C=C bond area
what are stereoisomers
- they have the same structural formulae but different spatial arrangement of atoms
how do E-Z isomers arise?
- when there is restricted rotation about the C=C bond
- two different groups attatched at both ends of the double bond
what is an electrophile?
- an electron pair acceptor
what happens if there are two identical groups on one side of the bond?
- E/Z isomers do not occur
give the reagent and conditions and type of reaction for reaction of bromine with alkenes
reagent - bromine
conditions - room temperature
reaction - electrophilic addition
why is bromine used as an electrophile?
- as bromine approaches the alkene, the high density electron area repels the electron pair in Br-Br bond
- this induces a dipole
- Br2 becomes polar and electrophilic
on a sheet of paper, draw the mechanism for the reaction of ethene and bromine
- arrow coming from the double bond onto the Br
- arrow from the Br-Br bond to the other Br
C+ formed, Br lone pair attacks the C+
give the reagent, conditions and type of reaction for reaction of hydrogen bromide with alkenes
reagent - HCl or HBr
conditions - room temperature
reaction - electrophilic addition
why is HBr polar?
- Br more electronegative than H
- H+ attracted to electron rich pi bond
what is Markownikoffs Rule?
- bromine will be added to the carbon with the least hydrogens attached to it
how does the stability of carbocations work?
- methyl groups on either side of the positive carbon are electron releaasing and reduce the charge on it, stabilising it
give the order of stability of carbocations
tertiary > secondary > primary
how is the major product formed?
- via the more stable carbocation
