The variation in
the oxidation state of the carbons may also be used to work out if
the organic half-rxn is an oxidation or reduction.
The following rules are used for
C-bonding.
1) if a bond is to H (or an atom <
EN than C)
then -1 is added to
C
2) if a bond is to O,
N, halogen (or an atom >
EN than C)
then +1 is added to C
3) if a bond is to another C then add 0 to C
eg. CH4 C -IV CH3CH3 C -III CO2 C +IV
CH3CH=CH2 ®
CH3CH(OH)C(OH)H2
-III -I -II -III 0
-I
Sum: -VI -IV + 2e-