Alkanes Flashcards
What is an alkane?
- a saturated hydrocarbon
- with sigma bonds between C-C and C-H bonds
- formed by a direct single overlap of orbitals directly between bonding atoms
BOILING POINT
As the chain length increases…
because…
so…
the boiling point increases
there is more surface contact between molecules
there are more induced dipole-dipole interactions between molecules which need more energy to overcome
BRANCHING
True or False
A branched isomer has a lower boiling point than an unbranched isomer
True
Why do branched alkanes have lower boiling points than unbranched alkanes?
There is less surface contact between molecules, leading to fewer induced dipole-dipole interactions which need less energy to break.
What is the reactivity of alkanes and why?
Relatively unreactive because the C-C and C-H bonds are
- non-polar
- strong
Also have a high bond enthalpy
What type of reaction is the combustion of alkanes and why?
Exothermic, because heat energy is released to the surroundings.
Alkanes are useful as…
fuels.
In a plentiful supply of oxygen, alkanes burn…
completely to produce CO2 and H2O.
In a limited supply of oxygen, alkanes burn…
incompletely to produce CO and H2O.
What is radical substitution?
A substitution type reaction because a H atom in the alkane molecule is replaced by a halogen atom.
What are the reagents and conditions for radical substitution?
-halogen and excess alkane
-UV radiation or 300 degrees Celsius
What is a radical?
A species with an unpaired electron.
What are limitations of radical substitution?
-can lead to the formation of a mixture of products due to further substitution
-there may be reactions at different positions in a carbon chain creating structural isomers
-low % yield of desired haloalkane
-separation by fractional distillation is costly
What are the steps in radical substitution?
Initiation
Propagation
Termination
