Organic ReactionsSCH4U – Unit B

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