Isomers
For each of the following:
1
2
3
Name the compounds shown.
Identify the structural isomers.
Identify the geometric isomers.
butane
methylpropane
but-1-ene
trans but-2-ene
propene
ethene
methylpropene
cis but-2-ene
IUPAC name = Alkanols
• CnH2n+1OH for saturated acohols
• Can be written R-OH
• Alcohols with three or more carbons form
structural isomers.
Alcohols
Alcohols
Naming and Structure
• -ol replaces the –e
• Parent chain contains –OH
• Position of hydroxyl group determines
numbering of alkyl groups (i.e count from
the lowest carbon chain)
• Prefix –di, -tri indicate multiple functional
groups
H
H
H
H
H – C – C – C – C – OH
H CH3 H H Butane
H
H
H
H
H – C – C – C – C – OH
H CH3 H H Butan-1-ol
H
H
H
H
H – C – C – C – C – OH
H CH3 H H 3-methylbutane-1-ol
Properties
• Hydrogen bonding due to –OH groups
creating polarity
– Determines physical properties for smaller
molecules
• Permanent dipoles and instantaneous
dipoles
– Non-polar hydrocarbon portion determines
properties for larger molecules
pH & Conduction
• Non-conductors
• Neutral solutions
Melting & Boiling Points
• Higher than corresponding alkane due to
hydrogen bonding
• Liquids at room temp up to 8Carbons
Solubility
• Up to 3 Carbon soluble in very water
• 4 Carbon soluble in water
• 5-6 Carbon slightly soluble
Solubility due to polarity
• >6 C insoluble in water due to large nonpolar alkyl (hydrocarbon) region.
• Commercial solvent as they can dissolve
both polar and non-polar substances.
1,2-Ethanediol
• Two hydroxyl groups = greater hydrogen
bonding
• Antifreeze
• Antiboil
• De-icing fluid
Alcohols II
Isomerism
Cis-trans isomers
1
2
3
4
5
Which of the following compounds will
have cis-trans isomers?
(Hint: Draw the structure.)
CHCl=CH2
The following have cis-trans
isomers
CH3CH=CHCH2CH3 2 CH3CH=CHCH2CH3
CHCl=CHCl
3 CHCl=CHCl
CH2=CBr2
5 CHBr=CBrCH3
CHBr=CBrCH3
Structural Isomerism
H
H
H
H – C – C – C – OH
H CH3 H
H
H
H
methylpropan-1-ol
H
H – C – C – C – C – OH
H H
H H
butan-1-ol
Primary, secondary, tertiary
• Determined by number of alkyl groups
attached to the same carbon as -OH
• Distinguished by Lucas reagent (ZnCl2 in
conc HCl)
– no visible reaction: primary alcohol
– solution turns cloudy in 3-5 minutes:
secondary alcohol
– solution turns cloudy immediately, and/or
phases separate: tertiary or benzyl
alcohol
Primary alcohols
• are those alcohols in which the carbon atom to
which the hydroxyl group ( OH) is attached has
only one carbon attached to it. (usually at the end
of the chain)
• I.e. the carbon with OH group is bonded to only one
other carbon atom.
E.g.
Secondary alcohols
• are those alcohols in which the carbon atom to
which the hydroxyl group ( OH) is attached has
two carbons attached to it
• E.g. Butan-2-ol
Tertiary alcohols
Tertiary alcohols
• are those alcohols in which the carbon atom to
which the hydroxyl group ( OH) is attached has
three carbons attached to it
Optical Isomers
A form of stereoisomerism
• In stereoisomerism, the atoms making up the
isomers are joined up in the same order, but still
manage to have a different spatial arrangement.
Why optical isomers?
• Optical isomers are named like this because of
their effect on plane polarised light.
• Simple substances which show optical isomerism
exist as two isomers known as enantiomers.
Butan-2-ol