Organic molecules with functional groups containing oxygen

96 Pages·2008·0.46 MB·English

Organic molecules with functional groups
containing oxygen
alcohols X = OH
O
X = C aldehydes
H
C,H
X
O
X = C ketones
O
carboxylic
acids X = C
OH
Key Skills
1. Dealing with structures (Bruice 1.4)
We need to understand the following concepts:
• Valency: the number of bonds that an atom must have
eg carbon: 4; hydrogen: 1; oxygen: 2
H H
• Bond Concept: a pair of electrons
H C C H
H H
C C C C
To break a bond, the To make a bond, a pair
electron pair has to move of electrons has to
away from the space move into the space
between the atoms between the atoms
• Drawing structures: we can represent a molecule in a variety of ways
Example: ethanol, C H O
2 6 CH
3
CH
2
H H
CH CH OH
3 2
C C OH H C C OH
OH
H CCH OH
3 2
H H
Never!! - A bit long Correct – Compact –
unless you mean winded – but useful if it is the
1,1,2,2- good if you space is an standard
tetramethylpropanol! want to use issue for large
the structure in molecules
a mechanism
The ability to “read” and draw structural formulae is an
absolutely essential skill!
Problem
How many hydrogens are on each of the carbons indicated below?
OH
OH
OH
OH
A very, very, very, common mistake!
≠
• What is the molecular formula of each of the above molecules?
• How many hydrogens are on each of the carbons?
• What is the name of each compound?
• Is there any other way of drawing the first structure?
2. Dealing with mechanisms (Bruice 1.18, 3.6)
• A mechanism is a description, in terms of the electrons involved, of how
the reactant molecule(s) changes into the product molecule(s). “Curly
arrows” are used to show how the electrons move during the change.
• Most reactions involve intermediates, the nature of which determine
the type of mechanism involved
reactant intermediate product
• Reactions can involve a neutral intermediate with an unpaired electron
(a radical) or a charged intermediate (a cation (+) or an anion (-))
Example: a reaction mechanism involving charged intermediates
H
H H ≡ H H
H H H
H SO
2 4 + H O
2
H C C O H H C C O C C
+ H
H H H H H H H
H
• The arrows are double headed in this case, indicating the movement
of a pair of electrons
• The arrows begin at a definite pair of electrons - a bond or a lone pair –
and move towards a positive charge
• If they move into the space between two atoms, a bond is formed
• If they move out of the space between two atoms, a bond is broken
• If a new bond is formed with a neutral atom, another bond involving
that atom has to be broken
• If an atom gains an electron, it acquires a negative charge; if an atom
loses an electron, it acquires a positive charge
The Chemistry of Alcohols
Functional Group
General Alcohols
δ−
R
O δ+
C,H R H
functional
group
δ−
Key Point: alcohols and water contain
O δ+
the same functional group (FG)
H H
Famous Alcohols
1. Ethanol
H H
• Structure H C C O H or H CCH OH or
3 2 OH
H H
• World Production (2006): 51 gigalitres (5.1 x 1010litres) – 69% from
the US/Brazil
• Methods of Production
(a) Hydration of ethene: production of ethanol for use as an industrial
feedstock
H H H PO on
3 4
crude
charcoal gas phase
oil C C + H2O H3CCH2OH reaction
300°C
H H
ethanol produced in this way is a
petrochemical: non-renewable/not
sustainable
(b) Fermentation
yeast
C H O H CCH OH + 2CO
6 12 6 3 2 2
no O
2
fermentable sugars such as
glucose, fructose or sucrose
(C H O )
12 22 11
H SO
malting -
2 4
involves the
enzyme corn (starch)
sugar
amylase (US):
cane
production of
(Brazil) barley:
ethanol a a fuel
production of
ethanol as a
beverage
(c) Cellulosic ethanol
Cellulose is a glucose polymer which makes up 38% of all plant matter but
which cannot be fermented directly
enzymic
hydrolysis
cellulose glucose
cellulase
fermentable sugar
materials such as straw, sawdust,
bagasse (residue after extraction
of sugars from sugar cane),
switchgrass (an “energy crop”)
(d) Bioethanol production in Ireland
The fluid left when the solids are removed from the milk during the making of
cheese is called whey and contains fermentable sugars. This is currently
the source of all bioethanol produced in Ireland. However the amount of
bioethanol available from this source would not be sufficient to satisfy the
demand for it as a fuel.