intro to mechanisms Flashcards
homolytic fission
each atom gets one electron from the covalent bond
what does a one headed arrow show?
movement of one electron
free radical
reactive species which possess an unpaired electron. free radicals do not have a charge and are represented by a dot
what happens when a bond breaks by homolytic fission?
forms two free radicals
heterolytic fission
one atom gets both electrons
what does a two headed arrow show?
movement of a pair of electrons
what does heterolytic fission produce
ions
why do we use curly arrows?
we use curly arrows in mechanisms to show the movement of an electron pair showing either breaking or formation of a covalent bond
where does a curly arrow start?
always from a lone pair of electrons or the centre of a bond
where will electrons move from
more negative areas to more positive areas
where can pairs of electrons be found
lone pairs or covalent bonds
addition
adding atoms onto a molecule
elimination
taking away atoms from a molecule
substitution
swapping atoms
oxidation
adding oxygen
reduction
removing oxygen
hydrolysis
splitting water, or splitting another molecule using water
polymerisation
joining many small molecules together
types of reaction/mechanism
addition
elimination
substitution
oxidation
reduction
hydrolysis
polymerisation
what condition is needed in free radical substitution
UV light
why dont alkanes generally react with many reagents
the C-C bond and the C-H bond are relatively strong
free radical substitution steps
initiation
propagation
termination
step one: initiation
essential condition: UV light
e.g. Cl2 = 2Cl*
what does the UV light do?
supplies energy to break the e.g. Cl-Cl bond. it is broken in preference to others as it is the weakest
UV light doesn’t have enough energy to break the C-H bond
step two: propagation
all propagation steps have a free radical in the reactants and the products
e.g. CH4 + Cl* = HCl + CH3*
CH3* + Cl2 = CH3Cl + Cl*
step three: termination
collusion of two free radicals does not generate further free radicals, the chain is terminated
e.g. CH3* + Cl* = CH3Cl
CH3* + CH3* = CH3CH3 (write this step using structural not molecular formulae)
Cl* + Cl* = Cl2
