Organic ReactionsSCH4U
Types of organic reactions• Addition• Elimination• Substitution• Condensation (dehydration synthesis)
▫Esterfication• Hydrolysis• Oxidation• Reduction• Combustion
▫Complete▫Incomplete
Addition• Reaction in which atoms are added to a
carbon-carbon double or triple bond• LOOK FOR: check if C atoms in product(s) are
bonded to more atoms than C atoms in reactant• Alkenes and alkynes generally react with one of
four reactants:▫H2, H-H example #1▫H2O, H-OH example #2▫Acid Halides, H-X (X = F, Cl, Br, I) example #3▫Diatomic Halogens, X-X example #4
Addition•Example #1
2-butenebutane
Addition•Example #2
2-butanol
2-butene
Addition•Example #3
2-fluoro butane
Addition•Example #4
2,3-difluoro butane
Addition•When adding halogens to an alkyne, a
total of four atoms can be added•The amounts of the halogen reactant must
be considered:▫Excess example #5▫Limited example #6
Addition•Example #5
(excess halogen)
2,2,3,3-tetrafluoro butane
Addition•Example #6
(limited halogen)
2,3-difluoro 2-butene
Addition•If the alkene/alkyne contains many C atoms
and is reacting with a small molecule, isomers may form example #7
•If the small molecule reacts with an asymmetrical alkene, can use Markinnikov’s rule to predict the more abundant isomer example #8
•Markovnikov’s rule: H atom of a small molecule will attach to C atom of double bond that is already bonded to the most H atoms
Addition•Example #7
•50% 2-bromo pentane•50% 3-bromo pentane
Addition•Example #8
2-bromo pentane
Elimination• Reaction in which atoms are removed from
an organic molecule to form a double bond• LOOK FOR: check if C atoms in product(s) are
bonded to less atoms than C atoms in reactant• Basically, this is the reverse of an addition
reaction• Methods of undergoing elimination reactions:
▫Heat and strong acid (catalyst) used for alcohols example #1
▫Heat and strong base (catalyst) used for haloalkanes example #2
Elimination•Example #1
Elimination•Example #2
Elimination•If an asymmetrical molecule undergoes an
elimination reaction, constitutional isomers can form example #3
•General rule: H atom most likely to be removed from C atom with most C-C bonds
•“The poor get poorer!” ▫opposite of Markovnikov’s Rule
▫Called Zaitsev’s rule
Elimination•Example #3
(major product)
(minor product)
Substitution•Reaction in which a hydrogen atom or
functional group is replaced by a different atom or functional group
•LOOK FOR:▫Two compounds react to form two different
compounds▫Carbon atoms are bonded to the same
number of atoms in product and reactant
Substitution• Alcohols and haloalkanes undergo substitution
reactions relatively easily▫Alcohol reacts with acids containing a halogen (HCl, HBr,
etc.) to produce a haloalkane example #1▫Haloalkane reacts with hydroxide to produce an alcohol
example #2• Haloalkanes also react with bases to undergo
elimination reactions▫Thus, hard to control reactions of haloalkanes with bases
• For the purposes of our course:▫OH– = substitution reaction▫NaOCH2CH3 = elimination reaction
Substitution•Example #1
ethanol chloroethane
Substitution•Example #2
chloroethane ethanol
Substitution•Alkanes also undergo substitution
reactions•Alkanes are relatively unreactive, thus a
lot of energy is required (UV light) to catalyze rxn
•Alkanes react with chlorine and bromine to form haloalkanes▫If enough of the halogen is present, a mix
of organic compounds forms example #3•Ultimately, because of the mix of
products, this process is not used to produce haloalkanes
Substitution•Example #3
Substitution•Aromatic hydrocarbons (benzene
derivatives) are also stable•Require a catalyst to react with chlorine
and bromine example #4
Substitution•Example #4
benzene bromobenzene
Condensation• Reaction in which two molecules combine to
form a larger molecule, producing a small, stable molecule, usually water, as a second product or functional group
• LOOK FOR: Hydroxyl group from one molecule and a hydrogen atom from a second molecule being removed, and water being produced
• EXTREMELY IMPORTANT IN BIOLOGY!• Generally forms an amide bond when it occurs
between ~COOH and ~NH2
Condensation•Example #1
carboxylic amine amide wateracid
R1
O
O
C
H
+R3
R2
NH + OHH
R1
O
C
R3
R2
N
Condensation•Example #2
O
O
R1
N C C
H
H
H
H
O
O
R2
N C C
H
H
H
H
O
O
R3
N C C
H
H
H
H+ +
O
R1
N C C
H
H
H
O
R2
N C C
H
H
O
O
R3
N C C
HH
H +OH2
OH2
Esterification (condensation)• Reaction of a carboxylic acid with an
alcohol to form an ester and water▫Specific type of condensation reaction example
#3▫Catalyzed by a strong acid H2SO4
• Flavours and smells of fruits and spices are due to ester compounds
• Can be duplicated in a lab▫Production of synthesized ester compounds used
to flavour juices, candies, etc. example #4 (cherry flavour)
Esterification (condensation)•Example #3
carboxylic alcohol esterwater
acid
OH
O
R1C R2OH+ H 2SO 4
O
R1C R2
O
+O HH
Esterification (condensation)•Example #4
benzoic ethanol ethyl wateracid benzoate
OH
O
CC
CH
CH
CH
CH
CH + OH
CH2 CH3 H 2SO 4
+CH3
CH2O
O
CC
CH
CH
CH
CH
CHOH2
Hydrolysis•Reaction in which a molecule is broken
apart by adding hydroxyl group from a water molecule to one side of a bond and hydrogen atom of same water molecule to other side of bond
•Basically, this is the reverse of a condensation reaction
•LOOK FOR: a large molecule containing an ester or amide reacting with water to produce to smaller molecules example #1
Hydrolysis•Example #1
ester water carboxylicalcohol
acid
R2O
O
R1
C+
O HH H
O
O
R1
C+ R2
OH
Hydrolysis•Both the condensation reaction and
hydrolysis reaction are catalyzed by acid example #2
•The double arrow indicates the reaction is reversible
•How can we control the direction of a reversible reaction to favour one side of the equation???▫EQUILIBRIUM! (Unit #4)
Hydrolysis•Example #2
carboxylic alcohol esterwater
acid
OH
O
R1C R2OH+
O
R1C R2
O
+O
HHH 2SO 4
Oxidation•Reaction in which a carbon atom
forms more bonds to oxygen atoms or fewer bonds to hydrogen atoms (orgo)
•Always occurs along with a reduction reaction
•For organic chemistry, focus only on the organic compound
•Some oxidation reactions can also be classified as elimination reactions
Oxidation•Occurs when organic compound reacts
with an oxidizing agent▫KMnO4 = potassium permanganate▫K2Cr2O7 = acidified potassium dichromate▫O3 = ozone
•Redox reactions are often left unbalanced examples #1-3
Oxidation•Example #1
•C atom has lost H atoms
O
R1
CR2
H
H + [O]
O
R1C
R2
Oxidation•Example #2
•C atom has gained an O atom
+ [O]
O
R1C
H
O
R1C
OH
Oxidation•Example #3
ethanol ethanal
+ [O]
O
C C
H
H
H
H
H HO
C C
H
H
H
H
Reduction•Reaction in which a carbon atom
forms fewer bonds to oxygen atoms or more bonds to hydrogen atoms (orgo)
•Always occurs along with an oxidation reaction
•For organic chemistry, focus only on the organic compound
•Some reduction reactions can also be classified as addition reactions
Reduction•Occurs when organic compound reacts
with an reducing agent▫LiAlH4 = lithium aluminum hydride▫H2/Pt = hydrogen gas over a platinum
catalyst•Redox reactions are often left
unbalanced examples #1-3•Redox reactions will be covered in greater
depth during ELECTROCHEMISTRY (Unit #5)!
Reduction•Example #1
aldehyde or ketone alcohol•C atom has less bonds to O atom
+ [H]
O
R1
C
R2
H
O
R1 C R2
H
Reduction•Example #2
alkene alkane•C atoms have more bonds to H atoms
+ [H]C C
H
H H
H
C CH
H H
HH
H
Reduction•Example #3
propanone 2-propanol
•C atom has less bonds to O atom
+ [H]
O
CH3
C
CH3
H
H
O
CH3 C CH3
Combustion• Type of reaction in which a compound
reacts with oxygen to produce the oxides of elements that make up the compound
• 2 types:1) Complete combustion: an excess of oxygen
reacts with a hydrocarbon and produces carbon dioxide and water vapour, and releases energy
2) Incomplete combustion: reaction that occurs when insufficient oxygen is present; all elements in the fuel will not combine with oxygen to the greatest extent possible
Combustion•Example #1
HC + O2(g) CO2(g) + H2O(g) + energy
•Example #2HC + O2(g) C(s) + CO(g) + CO2(g) + H2O(g) +
energy