Topic 6C - Alkenes Flashcards
6C.18
What is the general formula for an alkene?
C(n)H(2n)
6C.19
Alkenes and cycloalkenes are example of what type of hydrocarbons?
Unsaturated hydrocarbons.
6C.20
Double bonds are formed from which two types of bond?
Sigma bonds and Pi bonds.
6C.20
What are the three scenarios in which a sigma bond can form?
Form at the overlap of:
- Two s orbitals
- A p and an s orbital
- Two p orbitals
6C.20
What evidence is there for the existence of Pi bonds?
The C=C double bond enthalpy is not double the bond enthalpy of C-C single bond.
6C.20
What needs to happen for a Pi bond to form?
Two p orbitals must overlap sideways. Any rotation of the double bond means that they cannot overlap sideways.
6C.20
In a Pi bond where are the regions of electron density?
Above and below the plane of the molecule. These two regions restrict the rotation of the C=C double bond.
6C.21
What is an electrophile?
An electron pair acceptor. It is a positive ion or molecule with a vacant orbital that attack negative ions or negative centres of molecules.
6C.22
What the reagents and conditions needed to form an alkane from an alkene?
Reagent: Hydrogen
Catalyst: Nickel
Conditions: 150 degrees centigrade and at 5 atmospheres.
6C.22
Give an example of where catalytic hydrogenation is used in industry.
In the manufacture of margarine from unsaturated vegetable oils.
6C.22
In the production of margarine a solid metal catalyst is used. Suggest why.
The solid metal catalyst is heterogeneous to the oils so there is no difficult separating the catalyst from the products.
6C.22
Why is catalytic hydrogenation used in the production of margarine?
The vegetable oils need to change from oily unsaturated liquids to soft saturated fatty solids such as margarine.
