12.Alkanes Flashcards
Every carbon bond in an alkanes has ____ single bonds
Four
Larger/longer alkanes tend to have higher boiling points because?
Alkanes have induced dipole-dipole interactions between molecules
Longer and larger alkanes have more surface contact and electrons
They can form more induced dipole-dipole interactions
So more energy is needed overcome these
Branched alkanes have lower boiling point cause?
Branched alkanes can pack less closely together and they have smaller surface area
They can form less induced dipole-dipole interactions
Why can’t liquid alkanes be oxidised
Oxidisation is a reaction between gases
So liquid alkanes must be vaporised first
Heterolytic fission is described as
A type of fission where one of the atoms takes both of the electrons from the bonded pair
Two oppositely charged ions are formed
In Homolytic fission
The bond breaks evenly and each of bonded atoms receives one electron from bonded pair
Radicals with unpaired electrons are formed
Photochemical reactions are
Reactions that are started by light
Why do radicals become highly reactive
The have an unpaired electron
What happens in free-radical substitution and give a brief summary
Initiation- free radicals are produced by the energy from UV light
Propagation- radicals used up to carry a chain reaction
Termination-free radicals join together to make stable molecules
Explain why alkanes are unreactive
Alkanes only contain C-C and C-H sigma bonds, which have bond enthalpy so difficult to break
The burns are also non-polar
So don’t attract nucleophiles or electrophiles
What is the problem with free radicals substitution
When you ‘re trying to make a particular product you instead get a mixture of products
E.g. trying to make chloromethane and there is too much chlorine and some of remaining hydrogen in chloromethane will get walled off for chlorine to make dicloromethane
Give another problem with free radical substitution in terms of isomers formed
Radical substitution can happen at any point lasting carbon chain so a mixture of isomers are formed
Chlorine with propane produces 1-cloropropane and 2-chloropropane
