Transcript Intro to organic chemistry (orgo)

Organic Reactions
SCH4U
Types of organic reactions
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Addition
Elimination
Substitution
Condensation (dehydration synthesis)
▫ Esterfication
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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-butene
butane
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
O
R2
C
R1
O
+
H
carboxylic
acid
H
O
N
R2
C
R3
amine
R1
amide
N
+
H
R3
water
H
O
Condensation
• Example #2
H
H
N
H
C
R1
O
C
O
+
H
H
H
N
H
C
O
R2
H
H
N
H
C
O
C
+
H
H
H
N
H
C
O
C
O
R3
H
O
H
C
N
R1
H
C
H2O
O
H
C
N
R2
H
C
R3
+ H2O
O
C
O
H
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
O
O
C
R1
OH
+
carboxylic
acid
HO
R2
H2SO4
C
R1
alcohol
ester
R2
O
+
H
water
O
H
Esterification (condensation)
• Example #4
O
CH
O
C
HC
C
OH
HC
CH
+
CH
benzoic
acid
CH2 CH3
HO
CH
H2SO4 HC
C
C
HC
CH2
O
CH3
CH
+
CH
ethanol
ethyl
benzoate
water
H2O
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
O
O
C
R1
R2
+
H
O
O
ester
C
H
R1
water
carboxylic
acid
H
+
R2
H
O
O
alcohol
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
O
O
C
R1
OH
+
carboxylic
acid
HO
R2
H2SO4
C
R1
alcohol
ester
R2
+
H
H
O
O
water
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
H
O
R2
C
O
H
+
C
[O]
R1
• C atom has lost H atoms
R2
R1
Oxidation
• Example #2
O
C
R1
H
O
+
[O]
• C atom has gained an O atom
C
R1
OH
Oxidation
• Example #3
H
H
H
H
C
C
H
O
H
+
[O]
H
C
H
H
ethanol
ethanal
O
C
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
H
O
O
+
C
R1
[H]
R1
C
R2
H
aldehyde or ketone
alcohol
• C atom has less bonds to O atom
R2
Reduction
• Example #2
H
H
C
H
+
C
H
[H]
H
H
H
C
C
H
H
alkene
alkane
• C atoms have more bonds to H atoms
H
Reduction
• Example #3
H
O
O
C
H3C
+
[H]
H3C
C
CH3
CH3
H
propanone
2-propanol
• C atom has less bonds to O atom
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 #2
HC + O2(g)  C(s) + CO(g) + CO2(g) + H2O(g) + energy