Organic Reactions
Addition, Oxidation, Reduction,
Substitution and Elimination
1.) Addition
• Only occurs with double or triple carbon bonds
(on alkenes + alkynes)
– Double (and triple) C bonds are more reactive than
single bonds
C C
+ A
X
C C
A X
• A bimolecular molecule (A—X) breaks, and each
half attaches itself to a C on either side of a =
bond
– This breaks the = bond to make a single C-C bond
Addition
• So called because it makes a bigger molecule (adds
more stuff onto the alkene/alkyne)
• Things that will undergo addition with an alkene/alkyne:
– H2 – hydrogenation (usually requires a catalyst & high
temperature)
– X2 – I.e. Br2, Cl2, F2 – halogenation I.e. bromination (occurs
rapidly at room temperature)
– HX I.e. HCl, HBr, HI (hydrohalogenation – occurs at moderate
rates at room T)
– H2O – hydration (requires an acid catalyst, i.e. H2SO4)
• Addition is always exothermic
– from energy released by breaking C=C bond
Markovnikov’s Rule
• “The Rich Get
Richer”
– Where Hydrogen =
“riches”
• I.e. – when HX is
attached to an alkene
or alkyne, the H is
more likely to go on
the C that already
has the most Hs
Addition Examples
• CH2=CHCH3 + H2O 
+
• CH3CH=CHCH3 + Cl2 
• H-C≡C-CH2CH3 + HBr 
+
• H-C≡C-CH2CH3 + H2  H2C=CHCH2CH3
Addition Examples
• Benzene + Br2  no reaction!
• Aromatics don’t undergo addition!
– Not just with X2 (I.e. Br2), but with anything.
– Because the product would be less stable
than the resonance double bonds of the
benzene!
Uses: Hydrogenated Oils
• Unsaturated oils can be
hydrogenated to form
solid, saturated fats by
the reaction with
hydrogen gas in the
presence of nickel or
platinum as a catalyst.
• Ie: Margarine, shortening
(Crisco)
• Vegetable oils were first
hydrogenated for easier
transport and storage in
1911.
http://www.dvo.com/newsletter/monthly/2006/august/images/Crisco.jpg
Uses: Hydrogenated Oils
Uses: The Iodine Index
• The degree of unsaturation in oils can be
measured by measuring the amount of iodine
that can react with the unsaturated fat or oil by
addition. Each mole of C=C requires one mole
of I2 to react.
• The haloalkane chain is nearly colorless
Therefore unsaturated hydrocarbon chains will
destroy the purple brown color of iodine solutions
as long as there are C=C bonds present.
Uses: Bromine Test for
Unsaturation
• Like Iodine Index, we test for unsaturation
with Br2
– Usually done for non-fats, however (i.e.
cyclohexene, below, is a non-polar solvent)
H
H
+ Br2
H
Br
H
Br
2.) (Organic) Oxidation
• When an organic molecule is oxidized, it forms
more bonds to an Oxygen and fewer bonds
to a Hydrogen
– LEO says GER  still applies, but it’s easier to think
in terms of # of bonds to an oxygen or hydrogen
• I.e.
• For oxidation to occur, the C must be bonded
to at least one H at the start
(Organic) Oxidation
• Organic oxidation reactions are written:
• The [O] implies that the number of bonds to an
oxygen is increasing, but not necessarily the number of
oxygens in the molecule
• I.e.
(Organic) Oxidation
(Organic) Oxidation
• Needs an oxidizing agent (which is reduced)
– I.e. potassium dichromate (VI) solution (K2Cr2O7, in
the presence of H2SO4, KMnO4):
• Oxidizing agent pulls 2 Hs off primary alcohol
– Therefore pulls off electrons with the Hs: LEO
(Organic) Oxidation
• Oxidizing agent then donates an O to
the remaining H
• I.e.
Oxidation Examples
3.) (Organic) Reduction
• The exact opposite of organic oxidation
• Going backwards along this chain:
• Forms more bonds to an Hydrogen and fewer bonds
to a Oxygen
• Done by a reducing agent and a catalyst (I.e. H2 on
Platinum catalyst)
(Organic) Reduction
• Organic reduction reactions are written:
• The [H] implies that the number of bonds to a
hydrogen is increasing
– This has to increase # of Hs in the molecule
• To be reduced, a molecule can’t be saturated with Hs!
Reduction Examples
A Note about Organic Redox
• It’s not always obvious where the
electrons go (like regular redox)
– Sometimes there is no direct transfer of
electrons
• But there is always a change in Oxidation
state. I.e. Reduction:
Uses
• Pretty much everything, ever 
• Bleach oxidizes pigment molecules until they are no
longer the same molecule – lose their colour
• Cellular Respiration/Photosynthesis
– Cell Resp: Glucose oxidized to CO2
C6H12O6+ 6 O2  6 H2O + 6 CO2
– Each C molecule bonded to 2 Os in CO2, vs. 1 in
glucose
– Photosynthesis: CO2 reduced back to glucose
6 H2O + 6 CO2  C6H12O6+ 6 O2
Uses
• Ethanol conversion in the human body:
• People get sick from drinking because the enzyme
converting ethanol to acetaldehyde (alcohol
dehydrogenase) works faster than the one converting
acetaldehyde to acetic acid (acetaldehyde dehydrogenase)
– So acetaldehyde builds up – bad stuff
Uses
• Old breathalyzer tests:
• Ethanol in the bloodstream will come into equilibrium
with ethanol in the lungs
– I.e. when there’s ethanol in the body, it gets breathed out too
• The breathalyzer uses H2O to oxidize ethanol: it loses
electrons
• CH3CH2OH(g) + H2O(l)  CH3CO2H(l) + 4H+(aq) + 4e-
• The 4e- power an electrochemical cell; how much
voltage is produced is proportional to how much ethanol
is in the lungs and body!
Uses
• Problem with old breathalyzer tests: will
detect any kind of alcohol (I.e. ethanol
from mouthwash, acetone breathed out by
some diabetics, compounds in some
asthma inhalers!)
– New breathalyzers filter out acetone
– Breathalyzer tests are confirmed with blood
tests – screens for false positives