Chapter 12: Alkanes Flashcards
(19 cards)
Why dont alkanes react with most reagents?
Have strong single C–C and C–H sigma bonds and C–C/C–H bonds are non polar
What is the definition of an alkane?
It is a saturated hydrocarbon containing single C–C and C–H bonds as sigma bonds
What is a sigma bond?
The overlap of orbitals directly between the bonding atoms
What is the molecular shape and bond angle around each carbon atom?
Tetrahedral shape
109.5⁰
How does increasing the number of branches impact the boiling point of an alkane? Why?
Boiling point decreases
Less surface area / contact points for intermolecular forces because branches prevent molecules getting close together
Less total strength of attraction between alkane chains
Less energy / heat needed to break these forces
How does the length of the carbon chain impact the boiling point of an alkane?
Boiling point increases
More surface area / contact points for intermolecular forces
More total strength of attraction (london forces) between alkane chains
More energy / heat needed to break all the forces
Why are alkanes chemically unreactive?
Do not have any functional groups to take part in chemical reavtions
What are the products of complete combustion?
Carbon dioxide
Water
Energy (as heat)
What reactions do alkanes take part in?
Combustion
Halogenation
What are the conditions needed for complete combustion?
Plentiful supply of Oxygen
What are the products of incomplete combustion?
Carbon monoxide
Water
Energy as heat
Sometimes just carbon (as soot)
What are the causes of the incomplete combustion of alkanes?
Closed system
Poor ventilation
What are the three steps of halogenation?
Initiation
Propagation
Termination
What kind of reaction halogentaion an example of?
Radical substitution
What happens during Initiation?
Halogen molecule absorbs UV radiation
Halogen molecule undergoes homolytic fission to produce 2 reactive halogen radicals
What conditions are required for Halogenation?
UV radiation
What occurs during propagation?
A 2 step chain reaction:
- A halogen radical attacks a H atom of an alkane to produce an alkane radical and a hydrogen halide compound
- The alkane radical attacks another halogen molecule to produce a haloalkane compound and a halogen radical
What happens during termination?
2 radicals run into each other
Unpaired electrons pair up to form a covalent bond
Results in stable molecules then radicala are taken out
What are the limitations of radical substitution?
Further substitutions
Reactions at different positions in a carbon chain
