Download Topic 10. Organic chemistry

Topic 10. Organic chemistry
BBC News: Complex organic molecule found
in interstellar space
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Science reporter Michael
Eyre: ”Scientists have
found the beginnings of
life-bearing chemistry at
the centre of the galaxy.”
https://www.youtube.com/watch?v=UloIw7dhnlQ&list=PLCmjFQPlyHZJlg9G0l3I7Plr0-BK3W-a6
Introduction
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Organic chemistry: The study of carboncontaining compounds with the exception of the
allotropes of the element itself, metal carbonates
and its oxides and halides.
Organic compounds: Contain carbon and
hydrogen. They may
contain other elements too,
such as oxygen, nitrogen,
halogens or sulfur.
Inorganic carbon compounds:
● carbon oxides, hydrogencarbonates,
carbonates, cyanides
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Demo: sucrose + sulfuric acid
Carbon is a unique element
Carbon can form multiple bonds with itself and with
atoms of other elements (single, double and triple
bonds).
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The C-C bond is strong and thermally stable.
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Carbon atoms can also join to form rings.
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There are at least 6 million different organic
compounds, all with their own physical and chemical
properties.
In order to study all these organic compounds, they
are categorized into ”families” or homologous series.
Homologous series
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A homologous series is one in which all the members
have the same general formula.
The neighbouring members of the series differ by only
-CH2.
The alkanes form a series of compounds that all have
the general formula CnH2n+2
Some common homologous series
Homologous series Functional group
Alkanes
Alkenes
Halogenoalkanes
Alcohols
Aldehydes
Ketones
Carboxylic acids
Amines
Esters
Aromatic compounds Benzene
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Each functional group has its own characteristic reactions.
Formulas
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Empirical formula: The simplest whole number
ratio of the atoms in a molecule.
Molecular formula: The actual number of atoms in
a molecule.
Structural formula: How the atoms are bonded to
each other in a molecule.
Structural isomers
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Compounds with the same molecular formula but with
different arrangements of atoms.
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C4H10 (2 isomers)
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C5H12 (3 isomers)
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C6H14 (4 isomers)
C8H18
C9H20 has 35 isomeres
C20H42 has 366 319 isomeres
Naming organic compounds
Prefix
Where are the substituents?
- Parent
How many carbons?
- Suffix
What family?
e.g. 3-methylhexane
1. Identify the longest carbon chain (containing the
functional group).
Number of
carbons
1
2
3
4
5
6
Stem in IUPAC
name
methethpropbutpenthex-
2. Identify the type of bonding in the chain or ring
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Single bond: -an-
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Double bond: -en-
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Triple bond: -yn-
3. Identify the functional group/groups
Homologous
series
Functional
group
alkane
Suffix in IUPAC
name
-ane
alkene
double bond
-ene
alcohol
hydroxyl group
-ol
aldehyde
carbonyl
-al
ketone
carbonyl
-one
carboxylic acid
carboxyl
-oic acid
halogenoalkane
4. Identify the side chains or substituent groups
Side
chain/substituent
group
Prefix
methylethylpropylbutylfluoro-, chloro-, bromo-,
iodoaminohydroxy-
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If there are two or more functional groups in a
molecule, the order is:
carboxylic acid > ketone/aldehyde > alcohol > amine >
halide
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If there are more than one substituent group of the
same type, the following prefixes are used:
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mono-
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di-
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tri-
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tetra-
4. Numbers are used to give the position of groups or
bonds
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The carbon with the functional group should have the
lowest possible number.
Ex. Draw the structures and give the IUPAC names for
all non-cyclic isomers of:
Alkanes C-1 to C-6
Straight chain alkenes C-2 to C-6
Primary, secondary and tertiary carbon atoms
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Primary:
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Secondary:
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Tertiary:
The effect of the functional group on the
volatility
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The stronger the intermolecular forces, the higher the
boiling point.
Trends in boiling points
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As the carbon chain gets longer (= the mass of the
molecule increases) the van der Waals´forces of
attraction increases.
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Molecules with branches are
more spherical in shape,
which reduces the contact
area between them and
lowers their boiling points.
The effect of the functional group on the
solubility in water
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The greater the polarity of the functional group, the
more soluble in water the compound is.
As the size of the hydrocarbon chain increases, the
solubility decreases.
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Small molecules of alcohols, amines and carboxylic
acids are all water soluble and form hydrogen bonds.
e.g. ethanol dissolves in water, but hexan-1-ol is only
slightly soluble.
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Aldehydes, ketones and esters are less soluble in
water.
Halogenoalkanes, alkanes and alkenes do not
dissolve in water, but are soluble in other non-polar
solvents.
Propan-1-ol is a good solvent because it can dissolve
both polar and non-polar substances.
Crude oil
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Crude oil was formed over millions of years ago when the
remains of animals and plants were trapped under layers
of rock.
Crude oil is a complex mixture of many different organic
compounds, mainly alkanes.
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In an oil refinery the
alkanes are separated
(according to boiling
point) by fractional
distillation.
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The various fractions,
with different physical
characteristics, are used
in a wide variety of
circumstances, mainly as
fuels.
The molecules in the higher boiling fractions are
broken down (=cracked) in the presence of a catalyst
to give smaller more useful molecules.
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For example alkenes can be obtained in large
quantities from crude oil.
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Alkanes
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Alkanes are saturated hydrocarbons (= they contain
only single C-C bonds) .
Hydrocarbon: Compounds that ONLY contain
hydrogen and carbon.
General formula: CnH2n+2
Reactivity
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Alkanes are stable under most conditions, because of
strong C-C and C-H bonds and low polarity.
They only undergo combustion reactions with oxygen
and substitution reactions with halogens.
a) Combustion
Ex. Give a balanced
equation for the combustion
reaction of gasoline (C8H18)
in excess oxygen.
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The combustion reaction is highly exothermic, as the
bond enthalpies of the products are greater than
those of the reactants.
b) Substitution
Alkenes
General formula: CnH2n
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The double bond is made up of two different bonds:
The pi-bond is a weaker bond than the sigma-bond
and it is relatively easily broken.
Addition reactions:
With hydrogen = hydrogenation
With halogens = halogenation
With hydrogen halides
With water = hydration
Addition polymerization
Polyethene
Polypropene
Polychloroethene
Alkanes vs. alkenes
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Alkenes have a higher ratio of carbon to hydrogen
than alkanes and will burn with a much more dirty and
smoky flame (because they contain more unborn
carbon).
Aromatic compounds burn with an even smokier
flame.
Alkenes readily undergo addition reactions, whereas
alkanes will not.
Demo: Alkene test
Alcohols
a) Combustion
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Like the hydrocarbons, alcohols burn in oxygen with
the release of large amounts of energy.
Alcohols are therefore an important source of fuel.
Alcohols release less energy than hydrocarbons with
similar molar mass:
b) Oxidation
KCr2O7
An aldehyde is obtainded
if the product is distilled
off as it is formed.
A carboxylic acid is
obtained if the mixture is
heated under reflux.
Halogenoalkanes
Substitution reaction
Reaction pathways
In modern industrial organic chemistry a new compound
is produced by converting one compound into another.
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Important organic compounds are for example:
polymers, pharmaceuticals, dyes and solvents.
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The oil industry is the main source of the raw materials
for the organic compounds that are produced.
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Reaction pathways
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The starting compound has to be converted into the
desired product using as few steps as possible and
each step should have the highest possible yield.
The reaction pathway describes this sequence of
several steps between the starting material and the
product.
Ex. 1
Devise two-step syntheses of the following
products from the starting material listed. Include
any necessary experimental conditions and an
equation for each step.
a) Ethanoic acid from ethene
b) Butan-1-ol from butane
c) Hexan-3-one from 3-bromohexane
d) 1,2,3-trichloropropane from propene
e) Propanal from 1-bromopropane
Ex. 2
The synthesis of a particular organic product
involves seven separate stages. If each stage
produces a yield of 70%, calculate the percentage
yield of the final product.