Alkenes Flashcards
What is the general formula for alkanes
Cn H2n
What type of hydrocarbons are alkenes
Unsaturated hydrocarbons because they captain at least one double covalent bond between the carbon atoms
Alkenes will generally have less what?
Hydrogens
Why are C=C bonds unsaturated
Because they make more bonds with extra atoms in addition reactions
How many pairs of electrons are found in C=C and what does this result to?
• Two pairs of electrons
• High electron density
• Makes alkenes reactive
What type of alkene would have 2 Hs less than the equivalent open-chain alkene
Cyclic alkenes
What type of addition reaction happens with alkenes?
Electrophilic addition reactions
How do electrophilic addition reactions happen?
The double bonds open up and atoms are added to the carbon atoms
Why do electrophilic addition reactions happen?
The double bond has got plenty of electrons and is easily attacked by electrophiles
What are electrophiles
Electron pair acceptors
What charge do electrophiles carry and why?
Positive charge because they are short of electrons
What is used to test for in saturation
Bromine water
Describe the test for unsaturation
• Shake an alkene with orange bromine water
• The solution quickly decolourises
• Colourless dibromoalkane
• Via electrophilic addition
Name two compounds Alkenes undergo Electrophilic addition with
• Hydrogen halides
• Sulphuric acid
What is formed when alkenes react with hydrogen bromide?
Halogenoalkanes
Adding hydrogen halides to unsymmetrical alkenes form what two products
A stable (major product) and an unstable Carbocation (minor product)
What is the difference between a stable product and an unstable product
A stable product will have more alkyl groups so it will be produced more
What are the three type of carbocations?
Primary, secondary and tertiary
Draw the mechanism for the reaction of propene with hydrogen bromide
Check physical flashcards for answers
What conditions are required to react alkenes with sulphuric acid and what product is formed?
• Cold concentrated sulphuric acid
• Alkyl hydrogen sulphates
How are alkyl hydrogen sulfates formed into alcohols?
• Add cold water and warm the product
• It hydrolyses to form an alcohol
• The sulfuric acid is not used up, so it acts as a catalyst
Draw the mechanism for the reaction of ethene with sulfuric and cold water to form an alkyl hydrogen sulfate and an alcohol
Check physical flashcards for answers
What is carbocation
An organic ion containing a positively charge carbon atom
What is the iupac name of the major product of the reaction between 2-ethylbut-1-new and hydrogen bromide
3-bromo-3-methylpentane
Give the formula for percentage yield
Actual yield/Theoretical yield x100
Give the formula for atom economy
Mass of useful product/total mass of product x 100
State the importance of percentage yield and atom economy when choosing the method used to make a compound
• Yield: so you can use less starting material, reactants
• Economy: So makes less (waste) product
What areas are electrophiles attracted to?
electron rich areas
When do addition reactions occur?
Where there is a double bond
Explain why there is an attraction between a C=C double bond and Br2
• Double bond in C=C is electron rich
• Brs+ is attracted to to C=C
• Br-Br becomes polarised
What is the difference between addition polymerisation and condensation polymerisation
• In addition polymerisation, monomers are added together with no by-products, while in condensation polymerisation, monomers react with each other and release by-products like water or methanol
Give the conditions needed to favour an elimination reaction
• Alcoholic/ethanolic solvent
• Hugh temperature
• Hot under reflux
- What is an electrophile?
- What is addition?
- An electrophile is a lone pair acceptor
- Addition: Reaction which increases number of substituents or convert double bond to single bonds or where two molecules from one molecule
Explain why bromine, a non-polar molecule is able to react with propene
- electron rich
- Causes induced dipole in Br2
Explain why bromine, a non-polar molecule is able to react with propene
• Bromine has temporary dipole-dipole interactions between its molecules
• Attracted to an area of high electron density
