14.2- REACTION OF ALKENES Flashcards
Are alkenes used as fuels?
no
Why are alkenes not used as fuels?
their reactivity makes them very useful for other purposes
What is the reaction of alkenes typically?
electrophilic additions
What makes the carbon-carbon double bond a centre of high electron density?
the four electrons in the carbon-carbon double bond
What are electrophiles attracted towards on an alkene?
carbon-carbon double bond which is the centre of electron density
What can electrophiles use to bond with alkenes?
by using two of the four electrons in the carbon-carbon double bond
Where do hydrogen halides add on an alkene?
across the double bond
When hydrogen halides add across the double bond of an alkene, what is formed?
halogenoalkane
What can happen when the double bond is not exactly in the middle when a hydrogen halide is added?
there are two possible products
What do the alkyl groups have a tendency to do?
release electrons
What is the tendency of the alkyl groups to release electrons called?
positive inductive effect
How is the positive inductive effect sometimes represented?
by an arrow along their bonds to show the direction of the release
What does the electron-releasing affect of the alkyl groups tend to do to the intermediate carbocation?
stabilise the positive charge of the intermediate carbocation
What is the affect on the carbocation the more the alkyl groups attached to the positively charged carbon atom?
the more stable the carbocation is
Order the stability of a secondary carbocation, tertiary carbocation and primary carbocation?
tertiary
secondary
primary
What will the product from an asymmetrical alkene tend to come from?
the more stable carbocation
How fast do alkenes react with chlorine, bromine or iodine?
rapidly
What is produced when alkenes react with chlorine, bromine or iodine?
dihalogenoalkanes
How does a halogen add to the alkene?
across the double bond
What does the halogen act as when a halogen and alkene react?
electrophile
What are the two steps for when an alkene and halogen add?
formation of carbocation by electrophilic addition
rapid reaction with negative ion
What is the bromine water test?
when a few drops of bromine water (reddish-brown) is added to an alkene, solution decolourised
When bromine water is added to an alkene, why is the solution decolourised?
the products are colourless
At what temperature does the reaction occur when concentrated sulphuric acid adds across the double bond of an alkene?
at room temperature
Is it an exothermic or endothermic reaction when concentrated sulphuric acid adds across a double bond of an alkene?
exothermic
What is the electrophile in a sulphuric acid molecule?
partially positive charged hydrogen atom
What is formed when water is added to the product of the addition of concentrated sulphuric acid to an alkene?
an alcohol
What is reformed when water is added to the product of the addition of concentrated sulphuric acid to an alkene?
sulphuric acid
As sulphuric acid is reformed when water is added to the product of concentrated sulphuric acid and an alkene, what does the sulphuric acid act as?
catalyst
How can you predict the products with an asymmetrical alkene?
by looking at the relative stability of the possible carbocations that could form
Can water add across the double bond of alkenes?
yes
How is the water being able to add across the double bond on alkenes used industrially?
to make alcohols
At what conditions is water added across the double bond in alkenes to make alcohols? (4)
carries out with steam
suitable temperature
suitable pressure
acid catalyst i.e. phosphoric acid
Equation for when water is added across the double bond of ethene?
CH2=CH2 (g) + H20 (g) = CH3CH2OH (g)
