3.4 Alkenes Flashcards
What is the alkene functional group and what is significant about it?
- C=C double bond
- it is a region of high electron density
What is the shape and bond angle around the C=C double bond?
- shape: trigonal planar
- angle: 120 degrees
What 2 types of bonds form the C=C double bond?
A single C-C bond and a pi bond
What causes the pi bond to form?
When the p orbitals overlap
How does the presence of the pi bond affect the C=C bond?
Causes restricted rotation about the planar C=C bond
KEY DEFINITION: structural isomers
- compounds with the same molecular formula but a different structural formula
KEY DEFINITION: stereoisomers
- compounds with the same structural formula but a different arrangement of atoms in space
What causes E/Z isomerism?
Restricted rotation about the planar C=C bond
What must happen in terms of bonding for E/Z isomerism to occur?
- each C atom of the C=C double bond must be bonded to different groups
KEY DEFINITION: electrophile
An electron pair acceptor
How must curly arrows be drawn?
Start from a:
* lone pair
* covalent bond
Describe the process of electrophilic addition:
- the high electron density in the C=C group induces a dipole in the halogen molecule
- a pair of electrons is accepted by the delta + halogen atom
- the covalent bond between halogens breaks by heterolytic fission
- the lone pair of electrons on the single ion forms a new bond with the carbocation
KEY DEFINITION: hydrolysis
The breaking of a bond using water
Hydrogen sulphate alkene + water»_space;>
Alcohol + sulfuric acid
Why is the tertiary carbocation the most stable?
- it has the most alkyl groups attached to it
- they release electrons to stabilise the + charge of the carbocations
- positive inductive effect
What is a positive inductive effect?
When alkyl groups release electrons to stabilise carbocations
What can hydrogenation of alkenes be used for?
To produce margarine
IUPAC name for PVC:
Poly (chloroethene)
IUPAC name for PVA:
Poly (ethenol)
