Download Lecture 14 Organic and Biological Chemistry 1

4.1 Systematic Nomenclature
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Definitions
Molecular formula
 Number of atoms in a molecule (element or
compound) e.g. C2H4O2
Empirical formula
 Simplest whole number ratio of atoms in a
compound e.g. CH2O
Structural formula
 Shows the shape and arrangement of atoms in a
compound e.g. CH3COOH
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Definitions
Structural isomers
 Same molecular formula but different structural
formula
 e.g. C2H4O2
O
O
H
H
H
C
H
C
C
C
H
Ethanoic Acid
H
H
O
O
H
Methyl methanoate
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Definitions
Homologous Series
 Conform to a general formula
 Have the same functional group
 Similar chemical properties
 Physical properties gradually change
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Definitions
Saturated compounds
 No multiple bonds between carbon atoms
Unsaturated compounds
 At least one C=C or C≡C bond
Aromatic compound
 Contains a benzene ring
R
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Systematic Nomenclature
Organic compounds
Consist of:
 Hydrocarbon chain or ring which is non polar and
usually unreactive (when saturated)
 Functional group/s which are involved in chemical
reactions and affect physical properties of the
compound
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Naming Organic Compounds
Find the longest chain of carbons. If there is a
functional group it must be attached to one of
these carbons.
No. of carbon
atoms
Prefix
1
2
3
4
5
6
7
8
Meth
Eth
Prop
But
Pent
Hex
Hept
Oct
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Naming Organic Compounds
Identify side chains off the main carbon chain.
Naming includes number and type of side chains
and their position along the main chain.
No. of branches
of same type
2
3
4
Prefix
Di
Tri
Tetra
Name Methyl Ethyl
Propyl
Butyl
Alkyl CH3group
C3 H 7 -
C4 H 9 -
C2 H 5 -
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Naming Organic Compounds
Identify the Functional Group
Homologous Suffix
series
H
Alkane
-ane
H
Alkene
-ene
Alkyne
-yne
Alcohol
Aldehyde
-ol
-al
H
C
C
H
H
C
C
H
H
H
C
O
H
H
O
H
H
C
H
C
H
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Naming Organic Compounds
O
H
Homologous Suffix
series
Ketone
Carboxylic
acid
H
C
Carboxylate -oate ion
ion
H
H
C
H
-one
-oic acid
C
H
O
H
H
C
C
H
H
O
O
H
H
C
H
–
C
O
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Naming Organic Compounds
Homologous Suffix
Series
H
H
Amine
-amine
Amide
-amide
O
H
H
C
H
H
N
H
H
C
N
H
H
H
H
O
H
C
H
C
N
H
H
C
H
C
H
C
H
N
H
H
H
C
H
H
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Name the following systematically:
H
H
H
H
H
H
H
H
C
H
H
C
C
C
C
C
C
C
H
H
H
H
H
O
H
H
H
H
H
C
H
H
H
H
H
H
H
C
C
C
C
C
C
C
C
Br
Br
H
H
H
C
C
H
H
C
H
H
C
H
H
H
H
H
H
H
H
C
H
H
C
H
H
H
C
H
H
C
H
H
H
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4.2 Physical Properties
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Physical Properties
 Melting point tm
 Boiling point tb
 Solubility in water
 These properties are affected by the length of
the carbon chain and the functional group.
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Carbon Chains
 C–C bond is non polar
 C–H bond is virtually non polar
 Tetrahedral symmetry around each carbon
results in carbon chains being non polar.
 Polarity of a carbon compound is determined
by the polarity of the functional group/s
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Alkanes
Alkane
Tb oC
CH4 C2H6 C3H8 C4H10 C5H12
-162 -89
-42
-0.5
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•Non polar molecules
•Secondary forces are Dispersion forces
•Low tm/tb
•As chain length increases (molar mass increases).
Dispersion forces increase.
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Aldehydes
Aldehyde
Tb oC
CH2O C2H4O C3H6O C4H8O C5H10O
-19
20
48
75
103
•Polar functional group
R
H
C
•Secondary forces are dipoledipole interactions
O •tm/tb higher than corresponding
alkane
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Aldehydes
 Effect of the functional group on tb decreases as the
carbon chain length increases
Alkane
-162 -89 -42 -0.5
Aldehyde
-19 20
Difference
143 109 90
48
75
75.5
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Alcohols
Alcohol CH3OH C2H4OH C3H7OH C4H9OH C5H11OH
Tb oC
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H
R C O H
H
78
97
118
138
•Polar functional group
•Secondary forces are Hydrogen
bonds
•tm/tb are higher than the
corresponding alkane or aldehyde
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Alcohols
 Effect of the functional group on tb decreases as the
carbon chain length increases
Alkane
-162 -89 -42 -0.5
Alcohol
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Difference
227 167 139 118.5
78
97
118
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Carboxylic acids
Acid
CH2O2 C2H4O2 C3H6O2 C4H8O2 C5H10O2
Tb oC
O
101
141
163
186
R
•Very polar functional group
C
•Secondary forces are Hydrogen
bonds
O
H
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•tm/tb are higher than the
corresponding alkane or aldehyde or
alcohol
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Other Polar Functional Groups
H
R
C
H
•Amines: Hydrogen bonds
H
•Ketones and Esters:
Dipole-dipole
interactions
N
H
O
R
R
C
C
R
O
O
R
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Effect of functional group on Tb
H
H
H
C
C
H
C
H
C
O
H
C
H
O
•Propanoic acid: 141oC
C
C
O
•Methyl ethanoate: 57oC
H
H
H
C
H
C
O
H
H
O
H
H
O
H
•Ethyl methanoate: 55oC
H
H
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Solubility
“Like dissolves like”
 To determine the solubility of organic
compounds consider:
 The number and types of functional groups (Identify
the secondary bonding)
 The size/ length of the non polar carbon chain
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Solubility in water
 To be soluble in water an organic compound must
Hydrogen bond with the water.
 As the carbon chain increases the solubility
decreases
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4.3 Alcohols
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Alcohols
Ethanol production
 80% from fermentation of glucose C6H12O6
which is a monosaccharide.
 The glucose is obtained directly from fruits (e.g.
grapes) or from the hydrolysis of disaccharides
or polysaccharides (starch) from vegetables and
grains.
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Hydrolysis
 (C6H10O5)n +½nH2O ½nC12H22O11
polysaccharide
disaccharide
 C12H22O11 + H2O  2C6H12O6
disaccharide
monosaccharide
 Overall
 (C6H10O5)n +nH2O  nC6H12O6
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Ethanol production
 C6H12O6 2C2H5OH +CO2 H=ve
Conditions
 Presence of yeast
 Temperature of 20-30oC which is maintained so
the enzymes in the yeast catalyse the reaction.
 Almost complete absence of oxygen. Small
amount required for yeast metabolism but too
much will oxidise the alcohol
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Alcohols
•Primary alcohol
H
R
C
O
H
H
R
H
C
H
•Secondary alcohol
O
O
H
R
R
•Tertiary alcohol
C
R
R
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Oxidation of Alcohols
 Primary and secondary alcohols can be oxidised
by an oxidising agent like acidified dichromate
 Cr2O72–  Cr3+
orange
green
 Tertiary alcohols are NOT oxidised by
dichromate ions.
 This reaction and the products formed can be
used to identify the type of alcohol present
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Oxidation of Alcohols
Primary alcohols
 Oxidised to the corresponding aldehyde and
then carboxylic acid
H
H C
H
H
C
H
O
H
O H
H C
H C
H
O
H
C
C
H
H
O
H
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Oxidation of Alcohols
Secondary alcohols
 Oxidised to the corresponding ketone
H
H
H
H C
C
C H
H
O
H
H
O
H
H C
C
H
H
C
H
H
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