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CHAPTER TWO: ORGANIC CHEMISTRY
Organic chemistry is the chemistry of compounds containing carbon.
It is associated with living matter found in plants and animals, for
e.g. carbohydrates, fats, proteins, vitamins, hormones, enzymes,
drugs, wool, silk and linen. Perfumes, dyes, flavours, soaps,
detergents, plastics, petrol and oils are also associated with
organic chemistry.
Carbon is in group lV in the periodic table and can have a
maximum of four bonds.
HYDROCARBONS
Hydrocarbons are compounds that contain only carbon and
hydrogen.
Chapter 2/p1
ALKANES
Have only single bonds.
General formula:
CnH2n+2
The three simplest alkanes contain 1, 2 and 3 carbon atoms
respectively and are called methane (CH4), ethane (C2H6) and
propane (C3H8).
Others are butane (4C), pentane (5C), hexane (6C), heptane
(7C), octane (8C), nonane (9C) and decane (10C).
Chapter 2/p2
ALKENES AND ALKYNES
Alkenes have a double bond and is given by the formula:
CnH2n
An example of an alkene is propene.
H
H
H
H
C
C
C
H
H
Alkynes have a triple bond and is given by the formula:
CnH2n-2
An example of an alkyne is propyne.
H
H
C
C
C
H
H
Chapter 2/p3
AROMATIC COMPOUNDS
H
H
H
H
H
H
H
H
H
H
H
H
benzene
Chapter 2/p4
ALCOHOLS
Contain the functional group, - OH and are named by replacing
the ending ‘e’ of the corresponding alkane with ‘ol’.
CH3 – OH
CH3CH2 – OH
CH3CH(OH)CH3
methanol
ethanol
2-propanol
THIOLS
Sulfur analogues of alcohols and contain an – SH functional
group in place of an – OH group.
CH3 – SH
CH3CH(SH)CH3
methanethiol
2-propanethiol
PHENOLS
The – OH group is attached to benzene.
OH
Chapter 2/p5
ETHERS
An ether is formed during the dehydration of an alcohol.
CH3CH2 – OH
HO – CH3
ethanol
methanol
CH3CH2 – O – CH3
methyl ethyl ether
Ethyl ether known as ether – general anesthetic.
ALDEHYDES
Prepared by the oxidation of primary alcohols.
Contain a C = O functional group.
CH3CH2 – OH → CH3CHO
ethanol
ethanal
H
H
O
C
C
H
H
Chapter 2/p6
KETONES
Prepared by the oxidation of secondary alcohols.
H
H
OH H
C
C
C
H
H
H
H
H
H
O
H
C
C
C
H
2-propanol
H
H
propanone
CARBOXYLIC ACIDS
Prepared by the oxidation of aldehydes.
H
H
H
O
C
C
C
H
H
propanal
H
H
H
H
O
C
C
C
OH
H
H
propanoic acid
Chapter 2/p7
ESTERS
Produced by the reaction of a carboxylic acid with an alcohol.
H
H
H
O
H
C
C
C
H
H
H
propanoic acid
methanol
O
H + HO
C
H
H
H
H
O
C
C
C
H
H
H
O
C
H
H
methyl propanoate
AMINES
Derived from ammonia, NH3.
Aliphatic and aromatic amines.
H3C NH2
methylamine
H3C
NH
NH2
CH2CH3
methyl ethylamine
benzylamine (aniline)
Chapter 2/p8
HETEROCYCLIC COMPOUNDS
Ring compounds in which one or more of the carbon atoms are
replaced by nitrogen, sulfur or oxygen.
NH
pyrrole
N
pyridine
N
N
pyrimidine
H
N
N
N
N
purine
Chapter 2/p9
NAMING OF ORGANIC COMPOUNDS
Rule 1: Choose the longest carbon chain to base the
name upon.
Rule 2: Number the carbons in this longest chain
beginning at the end nearest the first branch point.
Rule 3: Identify and number the branches.
-CH3
-CH2CH -CH2CH2CH3 -CH2CH2CH2CH3 -CH2CH2CH2CH2CH
methyl ethyl
propyl
butyl
pentyl
Chapter 2/p10
EXAMPLE
Name the following molecule:
H
H
H
H
CH3 H
H
H
C
C
C
C
C
C
C
H
H
CH3 H
H
H
H
H
SOLUTION
The longest carbon chain is seven atoms long
CH3 CH3
C
C
C
C
C
C
C
Therefore our name will be based upon heptane.
Chapter 2/p11
We now number the chain to give the following
CH 3 CH 3
C
1
C
2
C
3
C
4
C
5
C
6
C
7
By numbering in this manner the branches are on the lowest
carbon numbers possible, i.e. C3 and C4.
We thus have a methyl group on C3 and a methyl group on C4.
We can now write the name as 3,4-dimethylheptane.
WHEN NAMING ORGANIC COMPOUNDS USE
HYPHENS TO SEPARATE NUMBERS AND LETTERS, AND
COMMAS TO SEPARATE NUMBERS.
Chapter 2/p12
FUNCTIONAL GROUPS
The chain is numbered in the direction that gives the highest
priority functional group the lowest possible number.
H3C
4
3
C
H2
H2
C
2
H3C
COOH
H2
C
5
6
C
H2
1
4
3
C
H2
H2
C
2
CHO
1
EXAMPLE
Name the following compound
H3C
H
H
H
O
C
C
C
C
Cl
CH3 H
OH
Chapter 2/p13
SOLUTION
The parent hydrocarbon is five carbons long
H
H3C
5
C
4
Cl
H
C
3
H
O
C
C
2
1
OH
CH3 H
The suffix will be –oic acid; The substituents are 3-methyl and
4-chloro.
Thus, we have 4-chloro-3-methylpentanoic acid.
Chapter 2/p14
EXAMPLE
Name the following compound
H3C
OH H
H
H
O
C
C
C
C
C
CH3 H
H
H
H
SOLUTION
The highest priority functional group is the aldehyde.
Thus the parent chain is numbered:
OH H
H3C
6
C
5
C
4
CH3 H
H
C
3
H
H
O
C
C
2
1
H
H
Therefore the name is 5-hydroxy-5-methylhexanal
Chapter 2/p15
ISOMERS
Compounds with the same molecular formula but with different
bonding arrangements called structural or constitutional isomers.
Consider the compound, butane (C4H10): CH3CH2CH2CH3
Can obtain two isomers for butane:
H
H
H
H
H
C
C
C
C
H
H
H
H
H
H
butane
H
CH3 H
C
C
C
H
H
H
2-methylpropane
For pentane, have three isomers:
CH3CH2CH2CH2CH3
pentane
H
CH3
CH3
CH3CHCH2CH3
2-methylbutane
H3C
C
CH3
CH3
2,2-dimethylpropane
Chapter 2/p16