Free Radical Substitution Reactions Flashcards
What are the conditions for a free radical substitution reaction
-UV light
-room temperature and pressure
What is a free radical
Species that has an unpaired electron so is therefore reactive
What is homolytic fission
When a covalent bond breaks and one of the bonding electrons goes to each of the atoms to produce free radicals
Reaction equation of alkane reacting with a halogen
Alkane + X2 ——> alkane substituted eg chloromethane + HX
What are the three steps of free radical substitution reaction
-initiation
-propagation
-termination
What occurs during initiation reaction
-Cl2——>2Clº
-initiated by energy from UV light which supplies the energy to break the Cl-Cl bond which is broken in preference to the others as it is the weakest, UV light does not have enough energy to break C-H bond
-homolytic fission- each atom gets one electron from the covalent bond to form a free radical
What occurs during propagation
-CH4+Clº——> HCl + CH3º(free radical as chlorine free radicals are very reactive and remove H from the methane leaving methyl free radical)
-CH3º+Cl2—-> CH3Cl + Clº
-all propagation steps have a free radical in the reactants and the products
-as Cl free radical is regenerated it can react with several more alkane molecules in a chain reaction
What occurs during termination
-collision of two free radicals does not generate further free radicals meaning the chain is terminated, propagation steps stopped by the consumption of free radicals which combine to form neutral molecules
-eg Clº+ Clº——> Cl2
-CH3º+Clº——->CH3Cl
-CH3º+CH3º——>CH3CH3
What is an initiation step
Generates free radicals
What is a propagation step
They involve a free radical and produce a new free radical
What is a termination step
One that involves two free radicals forming a covalent bond
