Download Powerpoint - Naming alcohols and their physical properties

AN INTRODUCTION TO
THE CHEMISTRY
OF ALCOHOLS
THE CHEMISTRY OF ALCOHOLS
CONTENTS
• Structure of alcohols
• Nomenclature
• Isomerism
• Physical properties
THE CHEMISTRY OF ALCOHOLS
Before you start it would be helpful to…
• Recall the definition of a covalent bond
• Recall the difference types of physical bonding
• Be able to balance simple equations
• Be able to write out structures for simple organic molecules
• Understand the IUPAC nomenclature rules for simple organic compounds
• Recall the chemical properties of alkanes and alkenes
CLASSIFICATION OF ALCOHOLS
Aliphatic • general formula CnH2n+1OH - provided there are no rings
• the OH replaces an H in a basic hydrocarbon skeleton
CLASSIFICATION OF ALCOHOLS
Aliphatic • general formula CnH2n+1OH - provided there are no rings
• the OH replaces an H in a basic hydrocarbon skeleton
PRIMARY 1°
SECONDARY 2°
TERTIARY 3°
NAMING ALCOHOLS
Alcohols are named according to standard IUPAC rules
• select the longest chain of C atoms containing the O-H group;
• remove the e and add ol after the basic name
• number the chain starting from the end nearer the O-H group
• the number is placed after the an and before the ol ... e.g butan-2-ol
• as in alkanes, prefix with alkyl substituents
• side chain positions are based on the number allocated to the O-H group
e.g.
CH3 - CH(CH3) - CH2 - CH2 - CH(OH) - CH3
is called 5-methylhexan-2-ol
STRUCTURAL ISOMERISM IN ALCOHOLS
Different structures are possible due to...
A Different positions for the OH group and
B Branching of the carbon chain
butan-1-ol
2-methylpropan-2-ol
butan-2-ol
2-methylpropan-1-ol
BOILING POINTS OF ALCOHOLS
Increases with molecular size due to increased van der Waals’ forces.
Alcohols have higher boiling points than
similar molecular mass alkanes
This is due to the added presence of
inter-molecular hydrogen bonding.
More energy is required to separate the molecules.
propane C3H8
ethanol C2H5OH
Mr
44
46
bp / °C
-42
just van der Waals’ forces
+78
van der Waals’ forces + hydrogen bonding
BOILING POINTS OF ALCOHOLS
Increases with molecular size due to increased van der Waals’ forces.
Alcohols have higher boiling points than
similar molecular mass alkanes
This is due to the added presence of
inter-molecular hydrogen bonding.
More energy is required to separate the molecules.
propane C3H8
ethanol C2H5OH
Mr
44
46
bp / °C
-42
just van der Waals’ forces
+78
van der Waals’ forces + hydrogen bonding
Boiling point is higher for “straight” chain isomers.
butan-1-ol
CH3CH2CH2CH2OH
butan-2-ol
CH3CH2CH(OH)CH3
2-methylpropan-2-ol (CH3)3COH
bp / °C
118
Greater branching =
100
lower inter-molecular forces
83
BOILING POINTS OF ALCOHOLS
Increases with molecular size due to increased van der Waals’ forces.
Alcohols have higher boiling points than
similar molecular mass alkanes
This is due to the added presence of
inter-molecular hydrogen bonding.
More energy is required to separate the molecules.
propane C3H8
ethanol C2H5OH
Mr
44
46
bp / °C
-42
just van der Waals’ forces
+78
van der Waals’ forces + hydrogen bonding
Boiling point is higher for “straight” chain isomers.
butan-1-ol
CH3CH2CH2CH2OH
butan-2-ol
CH3CH2CH(OH)CH3
2-methylpropan-2-ol (CH3)3COH
bp / °C
118
Greater branching =
100
lower inter-molecular forces
83
SOLVENT PROPERTIES OF ALCOHOLS
Solubility
Low molecular mass alcohols are miscible with water
Due to hydrogen bonding between the two molecules
Heavier alcohols are less miscible
Solvent
properties
Alcohols are themselves very good solvents
They dissolve a large number of organic molecules