Transcript 2010-09-16 Alcohols

Group 7
Alcohols
Today's Starter Quote
When one door closes,
another opens; but we often
look so long and so regretfully
upon the closed door that we
do not see the one which has
opened for us.”
– Alexander Graham Bell
The simple way to think of alcohols is that there is a water
molecule where the hydrogen at one of the termini is replaced
by a carbon chain. The alcohol present in beverages is ethanol,
which is the mildest depressant and narcotic poison of all
alcohols. Other alcohols magnify this effect and are often
added to ethanol in the lab to make it unpalatable.
The addition of the OH group will drastically change the
properties of the related hydrocarbon. This is due to the polarity
of the molecule from a non-polar hydrocarbon, as well as the
possibility of forming stable hydrogen bonds.
Ethane is non-polar
Mild intermolecular
forces are easily broken
(www.elmhurst.edu, 2010)
Ethanol is polar and will have a σ+ H
terminus at the OH group and a σ –
oxygen atom adjacent to it.
Water will have a smiliar structure,
however due to its smaller size the
molecule is more polarized.
These σ+ and σ – ends are attracted
to one another in solution. This
creates a very strong network of
hydrogen bonds. These networks are
significantly more difficult to break.
The result?
The boiling point of ethane is –89 °C, while ethanol
will boil at 78 °C!
In the IUPAC naming system, the OH functional group changes
the suffix from 'ane' to 'anol' at the ending of the chain. The
parent alkane is the longest chain that contains that OH group.
CH3OH
methanol Highly toxic, leading to blindness
CH3CH2OH
ethanol
Used in beverages, vanishes,
lacquers and perfumes
CH3CH2CH2OH
1propanol
Solvent for waxes, found in brake
fluid
and death
CH3CH(OH)CH3 2-
propanol
(ispropanol, rubbing alcohol)
Used in the manufacture of gums,
oils and acetone
Classification of alcohols:
Alcohols are categorized based on the type of carbon that they
are attached to. Since carbon atoms have 4 bonds, the atom that
has the OH can be attached to 1,2 or 3 alkyl groups as well. This
creates primary, secondary and tertiary alcohols respectively. The
classification is important for the types of reactions that each will
undergo because the products are determined by the availability of
H atoms in key positions.
CH3CH2CH2CH2(OH)
CH3CH2CH(OH)CH3
CH3C(CH3)(OH)CH3
1- butanol
primary alcohol
2-butanol
secondary alcohol
2-methyl-2-butanol
tertiary alcohol
The Lucas test will allow us to determine the identity of each
alcohol. The 3 ° alcohol reacts instantly, the 2 ° alcohol reacts
slowly (6 minutes) and the 1 ° alcohol will not react.
Creating Alcohols – Making Aldehydes and Ketones
A hydration reaction is an addition reaction that adds the two
components of water across a unit of unsaturation. The reaction
often requires acid as a catalyst to break the water moecule into H +
and OH-. The reaction may occur as :
H2SO4
Propene +
water
-->
2-propanol
The reverse reaction is an elimination (dehydration) reaction
Markovnikov’s rule: ‘the rich get richer’
When adding a substance such as water to an unsaturated
hydrocarbon. The hydrogen will add to the carbon which already
has more carbons. This is why in the example above 2-propanol is
formed much more readily than 1-propanol. Another example
would include :
1-butene
+
hydrogen bromide
1-bromobutane