3.4- Alkenes Flashcards
What is the general formula for a alkene
CnH2n
Why are alkenes vulnerable to attack by electrophiles
. Bonds are exposed and have high electron density
.Double covalent bond consists of one sigma and one pi bond
. The pi bond is the exposed bond
What is the definition of stereoisomerism
Stereoisomers have the same structural formulae but have a different spatial arrangement of atoms
When do E-Z stereoisomers arise
.There is restriced rotation around the C=C double bond
.There are two different groups/atoms attached both ends of the double bond
How would you determine the priority groups on both sides of the double bond
The atom with the bigger atomic number is classed as the priority atom
What is an electrophile
An electrophile is an electron pair acceptor
What is the mechanism and the reagents/conditions for Alkene > Dihalogenoalkane
Reagent - bromine
Conditions- Room temperature not in UV light
Mechanisms- Electrophillic addition
.As the Br2 approaches the alkene the pi electrons repel the pair in Br2 and induce a dipole to form the electrophile
What is the mechanism and the reagents/conditions for alkene > halogenoalkane
Reagent- HCl or HBr
Conditions- Room temperature
Mechanism- electrophillic addition
what is markownikoffs rule
In most cases the halogen will be added to the carbon that has the fewest amount of hydrogens already attached to it
Why can some carbocations be more stable than others
The methyl group son either side of the positive carbon are electron releasing and reduce the charre on the ion which stabilises it
What is the mechanism and the reagents/conditions for alkene > alkyl hydrogenosulfate and then to alcohol
Stage one-
Reagents- Concentrated H2SO4
Conditions- Room temperature
Mechanism- Electrophillic addition
Stage two-
Reagents- Water
Conditions- Warm mixture
Type of reaction- hydrolysis
What is the reagents/conditions for the direct industrial hydration of alkenes to form alcohols
High temperature- 300-600 C
High pressure- 70 atm
Catalyst- Concentrated H3PO4
this reaction can be called hydration where water is added to the molecule
How would you test for an alkene
You would use bromine water which decolorises in the prescense of a double bond
What are addition polymers
Addition polymers are formed from alkenes
What is polychloroethene
. Waterproof and an electrical insulator, does not react with acids
. In its pure form it is a rigid plastic because of the strong intermolecular bonding between the polymer chains
. It is used to make uPVC window frame coverings and guttering
. If a plasticiser is added the intermolecular forces are weakened which allow the chains to move more easily resultign in more flexibility in the polymer
.PVC is used to make insulation on electrical wires and waterproof clothing
