topic 6c- alkenes Flashcards
state the general formula for all alkenes
Cn H2n
what are unsaturated hydrocarbons?
compounds of ONLY hydrogen and carbon which have at least one C=C bond
what is the general formula for cycloalkenes
Cn H2n-2
name the two types of C=C double bonds
SIGMA bond= axial overlap -> strongest
PI bond= sideways overlap between 2 p-orbitals
what is an electrophile?
electron pair acceptors - anything that is attracted to a negative charge and a lot of electrons
give examples of molecules or ions that are electrophiles and nucleophiles
electrophiles= H+, H3O+, NO2+
nucleophiles= CN-, OH-, H2O, NH3
addition of hydrogen
name the reactants used in a hydrogenation reaction
C2H4 (ethene) + H2 -> C2H6 (ethane)
ethane= alkane
name the two conditions needed in hydrogenation
- a nickel catalyst
- 150 ‘c
how is margarine produced?
- hydrogenation
-‘hydrogenating’ unsaturated vegetable oils
- removing double bonds -> raise MP -> solid at room temp
adding a halogen (Br)
describe the reactants in halogenation and the mechanism involved
C2H4 + Br2 -> C2H4Br2
- double bond repels Br2 electrons -> polarisation
- heterolytic fission of Br2 -> Br2 close to the C hands over electrons to Br2 farther away
- creates a positively charged carbocation
C2H4Br2= dihalogenoalkane = 1,2- dibromoethane
describe the test to identify an unsaturated hydrocarbon.
- shake an alkene with brown bromine water
- decolourises (due to Br is added across the double bond)
- 1,2- dibromoethane is formed (colourless)
describe the reaction of the addition of hydrogen halides
C2H4 + HBr -> C2H5Br
describe the reaction of hydration
C2H4 + H2O (steam) -> C2H5OH
- catalyst= phosphoric acid (H3PO4)
what are the conditions for hydration reaction?
- steam
- Heat 300’c 60 atm
- catalyst (H3PO4)
describe the reaction of oxidation to diol
C2H4 + acidified potassium manganate (VII) (H+/ MnO4-) -> ethane-1,2-diol
