10 alkanes

what is a (free) radical?

• is a species with an unpaired electron

• very reactive

• formed in radical substitution reactions

what is homolytic fission?

• a covalent bond breaks by homolytic fission, where each of the bonded atoms takes one of the shared pair of electron from the bond

what is heterolytic fission?

• a covalent bond breaks, one bonded atom takes two of the shared pair of electron from the bond

• forms 2 radicals

how reactive are alkanes, and why?

• low reactivity

• strong C-C and C-H sigma bonds

• non-polar → little EN

what is complete combustion?

• reaction of excess oxygen

• produces CO2 + H2O

• CₙH₂ₙ₊₂ + (3n+1)/2 O₂ → nCO₂ + (n+1)H₂O

what does incomplete combustion produce?

• occurs with limited oxygen

• CO carbon monoxide (toxic, binds to haemoglobin)

• C (soot)

• H2O

steps of radical substitution

1. initiation:
   Cl₂ → 2Cl· (UV)

2. propagation:
   Cl· + CH₄ → HCl + CH₃·
   CH₃· + Cl₂ → CH₃Cl + Cl·

3. termination:
   radicals combine:
   Cl· + Cl· → Cl₂
   CH₃· + CH₃· → C₂H₆

Cl• + •CH3 → CH3Cl

substitution

• replacement of an atom group of atoms with another atom or group of atoms

• e.g CH4 + Br2 → CH3 + HBr

addition

elimination