3Alkenes (4) Flashcards
(29 cards)
What’s a carbocation
Ion with a positively charged carbon atom
What’s an electrophile
Electron pair accepting group
What’s the general structure of an alkene
CnH2n
What’s alkenes functional group
C=C
What does a carbon=carbon bond consist of
Sigma bond and a pi bond
Where does the pi bond lie
Above and below the sigma bond
What is the rotation like around a double bond
There’s no rotation
This results in geometric isomers (cis/trans E/Z)
Where does the double bond sit
On a plane
What are the angles between each bond
Roughly 120 degrees
How does the bond enthalpy compare to the enthalpy of a single Carbon-carbon bond
C=C has a much higher bond enthalpy
What area is electron rich in an alkene
The double bond which can easily attract electrophiles
How does electrophilic addition happen
Undergoes via carbocation
What are the main products of electrophilic addition determined by
The stability of the carbocation
What is hydrogenation
When ethene reacts with hydrogen in the presence of a finely divided nickel catalyst at a temp around 150 degrees Celsius
Ethane is produced
What are the uses of hydrogenation
Manufacture margarine from unsaturated vegetable oils in palm and sunflower seeds
Veg oils are liquid, have double bonds (cis). These get converted to C-C bonds turning liquids into spreadable fatty solids
What is the reaction between alkenes and steam
React in the presence of phosphoric acid catalyst to produce alcohols
Generally is reversible
570k, 65 atm pressure
What is the reaction between alkenes and halogens?
Chlorine and bromine react rapidly with alkenes at room temp to form dihalogenoalkanes via electrophilic addition.
Reaction with iodine is slower
-reaction with bromine water is the qualitative test for alkenes= shake alkene with it and orange solution turns colourless
What happens when alkenes react with hydrogen halides
Possibility1=
React readily at room temp to form halogenoalkanes
Unsymmetrical alkenes will form a major and minor product
Possibility2=
Is exothermic
Room temp
Sulphuric acid acts as a catalyst and the product is an alcohol
What are alkenes
Unsaturated hydrocarbons
What are the carbocations in increasing stability due to positive inductive effect
Primary ion
Secondary ion
Tertiary ion
How are addition polymers formed?
From alkenes and substituted alkenes
What are the typical uses of polychloroethene (PVC)
Building and construction
Pipes and ducting for cables
How can polychloroethenes properties be modified using a plasticiser
Plasticisers are added to increase the distance between the polymer chains to disrupt the van der waal forces between the chains making them weaker
This means the chains can slide over each other making it more flexible
How to draw the repeating unit of a polymer
The polymer structure without brackets
Include long bonds at the end of
