Nomenclature
Thursday, 21 March 2019
A vast number of carbon compounds exist because:
1. The carbon atom is tetravalent (each atom can form bonds with four other atoms)
2. The carbon atom itself is relatively small
Hydrocarbons are compounds containing JUST hydrogen and carbon.
They are divided into homologous series based on what functional groups they have.
When naming hydrocarbons, the prefix (meth-, eth-, prop-, but-, etc.) delineates the
number of carbons and the suffix (-ane, -ene, -yne) delineates what series they are part of.
Numbers are added in to indicate the presence of branches.
Each homologous series has a specific formula revealing how many hydrogens are present
per carbon.
Alkanes (CnH2n+2) are the most basic forms of hydrocarbons, with only single bonds.
Alkenes (CnH2n) have a double bond between two or more carbons, and alkynes (CnH2n-2)
have a triple bond. Numbers are added to indicate the presence of non-single bonds as well
as the presence of branches.
When listing branches, first put the position number/s, then any prefix for number of groups
(di-, tri-, tetra-, etc.), then the prefix for number of carbons (meth-, eth-, etc.) and the suffix
‘-yl’. Arrange the names of the branches in alphabetical order, ignoring ‘di-’ or ‘tri-’ prefixes.
Haloalkanes are hydrocarbons with an added halogen such as chlorine, bromine, or iodine.
When naming haloalkanes, use the same rules as naming normal alkanes and treat the
halogens like branches: the position number/s, then any prefix for number of groups (di-,
tri-, tetra-, etc.), then the halogen name (chloro-, bromo-, etc.).
Arrange the names of the branches in alphabetical order AFTER the branches, ignoring ‘di-’
or ‘tri-’ prefixes.
Alcohols are hydrocarbons with a hydroxyl functional group (OH). Alkanols are a subset of
alcohols and are defined by having only single bonds – basically, branched or unbranched
alkanes but with added hydroxyl groups.
Other alcohols include hydroxybenzene.
Alcohols/Alkanols where the hydroxyl group is attached to a terminal carbon (which is only
bonded to 1 other carbon) are Primary alcohols. Secondary alcohols have hydroxyl-attached
carbons bonded to 2 other carbons and Tertiary alcohols have hydroxyl-attached carbons
bonded to 3 other carbons.
A number is used to indicate the position of the functional group just like for ethyl groups,
but this is placed between the prefix (meth-, eth-, etc.) and the suffix ‘-ol’.
Aldehydes and Ketones have carbonyl functional groups (C=O double-bonded oxygen) but
are different because of where these are positioned. Aldehydes are the Primary version
(with suffix -al) while Ketones are the Secondary version (with suffix -one).
Alkanals (alkanes with a terminal carbonyl group) are a subset of aldehydes and alkanones
(alkanes with a non-terminal carbonyl group) are a subset of ketones.
Carboxylic Acids have carboxyl functional groups (O=C-OH or COOH), and these functional
groups must always go on the end carbon. They include our old friend ethanoic acid (acetic
acid), CH3COOH.
Amines and Amides are hydrocarbons that also contain a nitrogen molecule!
Amines have an ammonia (NH2) functional group and the '-amine’ suffix.
Amides have an NH2 and oxygen (O=C-NH2 or CONH2) functional group and the ‘-amide’
suffix.
Physical Properties
Thursday, 2 May 2019
Alkanes form long 'strings' of carbons, while alkenes form different shapes depending on
the placement of the double bond and alkynes mainly form linear molecules. This is due to
valence shell electron pair repulsion theory (VSEPR theory).
Volatility
Intermolecular bonds regulate a substance's melting/boiling points and whether it is soluble
in water. When looking at organic compounds, there are a variety of things to consider.
Hydrocarbons are extremely volatile and vaporise/boil at low temperatures/pressures,
especially short-chain hydrocarbons. The larger compounds have more dispersal forces and
hence higher melting/boiling points. Alcohols and other organic compounds are also fairly
volatile and follow this trend, but due to their polar natures they are capable of dipoledipole bonds and even hydrogen bonding.
Volatility poses a safety risk as hydrocarbons are toxic to humans and highly flammable/
explosive. As such, gaseous hydrocarbons are stored under high pressure and have added
odours for early warning of leaks. All hydrocarbons are stored in sturdy, well-maintained
containers (gas bottles have a 7-year working life) with warning labels.
Transport and disposal of hydrocarbons is also significant – static electricity dispersion is
used on tankers, and hydrocarbons are disposed of by licensed agencies.
Solubility
Solubility depends on the homologous series first and foremost. Hydrocarbons (alkanes,
alkenes, and alkynes) are non-polar and thus NOT soluble in water, but they are soluble in
other non-polar substances.
Aldehydes and ketones are slightly soluble in water due to polarity, as the oxygen function
group is more electronegative than the rest of the molecule. Hence, they have dipole-dipole
bonding (especially aldehydes which also have a more polar structure).
Alcohols, carboxylic acids, amines, and amides are all very soluble in water because they
contain either a OH or an NH2 functional group, making them capable of hydrogen bonding,
as well as some dipole-dipole bonds. However, they are also soluble in non-polar substances
due to their 'tail' of carbons, which is useful to mix stuff like oil and water.
All organic compounds are more water-soluble when they are smaller, because when the
non-polar carbon 'tails' get too long they block water molecules from reaching the
functional groups to hydrogen bond and the dispersion forces take over.
Chemical Reactivity
Alkanes are relatively unreactive due to the very stable non-polar C-H bonds, which require
a lot of energy to break them. However, they are very combustible and will also react with
halogen molecules to form halogenoalkanes.
Octane is recognizable as a fuel source for vehicles, and combusts with the formula:
2C8H18 (l) + 25O2 (g) --> 16CO2 (g) + 18H2O (g)
Obviously incomplete combustion will also produce CO and Carbon (soot).
Alkanes will react with halogen free radicals: Initiation occurs when a reactive diatomic
molecule (typically a halogen such as Br2 or Cl2) is split by UV light or very high
temperatures. Propagation then occurs as the chlorine radicals destructively bond with
atoms from anything around them, leaving the 'thing' (e.g. an alkane) as a radical.
Termination is when the reaction eventually completes through two radicals reacting
together.
Alkenes are more complex than alkanes and can react in a greater variety of ways. This is
because of the high electron density of the double bond, which makes it stronger but less
stable. As well as combustion and radical reactions they can also undergo addition
reactions.
Hydrogenation is where the unsaturated C=C double bond breaks in the presence of
Hydrogen (this requires palladium/platinum/nickel catalysts) and Halogenation is where the
bond breaks due to X other molecules (e.g. Br2) to form a saturated X-C-C-X bond. No UV or
heat is required (spontaneous reaction), and only one type of product is produced – this is
why it is called 'addition'.
Hydrogen halides also react spontaneously with alkenes, and their positioning when
bonding affects the isomer produced. Markovnikov's rule states that if a hydrogen is added
to an alkene, it will bond with the carbon that already has the most hydrogens.
At very high temperatures and pressures, gaseous water (steam) reacts with alkenes to
produce ethanol. This is an equilibrium reaction that occurs with the aid of a dilute H2SO4
catalyst and which is essential for many industrial processes. This is called oxidation.
Alkenes can also react with cold, dilute, alkaline potassium permanganate to produce a diol
(alcohol with 2 OH groups).
Amines are basic, amides are neutral, and carboxylic acids are acidic!
Combustion
Like most organic compounds alcohols will burn readily in air to form carbon dioxide and
water: C2H5OH(l) + 3O2(g) --> 2CO2 + H2O(g)
As usual, this is highly exothermic and if the supply of air is restricted, incomplete
combustion may occur producing CO or C.
Fuels
Monday, 3 June 2019
Fossil Fuels
There are three main types of fossil fuels: oil, gas, and coal. These fuels are formed over
millions of years and are hence 'non-renewable'. First, energy from the sun is stored
through photosynthesis in plants (coal) and ocean organisms (oil) through the equation
6CO2 + 6H2O --> C6H12O6 + 6O2 + ΔH. These are compressed under layers of silt and
sediment over millions of years, storing the energy through converting the glucose and
starch to hydrocarbons.
Natural gas is made up of a mixture of methane, ethane, and propane and is often found
near oil and coal deposits.
Oil is made up entirely of alkanes of different chain lengths and is useless to us when
unprocessed.
In order to separate the different parts, a process called fractional distillation is used. The oil
is heated in a furnace until it is completely vaporised (400oC), then pumped into a fractional
distillation column where different chain lengths cool at different points.
Biofuels
There are three main types of biofuels: biogas, biodiesel, and bioethanol.
They are produced in a matter of months rather than millions of years and are hence
renewable.
While bioethanol produces less CO2 per mole, it is also less energy-efficient (meaning you
need more) and involves more work and CO2 production to make (farming, fermenting,
fractional distillation).
This means overall bioethanol DOES NOT release less CO2 than fossil fuels. However, it does
release less particulates and CO, and it is biodegradable (no oil spills).
Alcohols are an important fuel, used in alcohol burners and other heaters. Some vehicles
now use alcohols as fuels or use it in various blends to extend the fuel, e.g. E10. In Australia,
due to the water-absorbing nature of ethanol, pure ethanol fuel is not available as car
manufacturers will not provide warranty for it. The amount of energy released per mole
increases with the size of the alcohol as more CO2 molecules are made. However, the
smaller molecules give more energy per gram/per litre.
Impact of Carbon-Based Fuels
Hydrocarbons are reliable fuel sources that can be mined easily using modern technology
and which have a very large output of energy compared to the amount of energy that must
be used to produce them. The use of hydrocarbon fuels has created an economic boom and
allowed for readily available electricity and transport. However, they also lead to health
issues and are the main cause of modern climate change.
Alcohol
Thursday, 30 May 2019
Production of Alcohol
The hydration of ethylene is an addition reaction which produces ethanol for industrial
purposes. For non-industrial purposes, ethanol is typically produced by fermentation:
C6H12O6  2CH3CH2OH + 2CO2
This is done naturally by yeast in a sugar solution at controlled temperature conditions of
35-40°C and anaerobic conditions (absence of oxygen). The concentration of alcohol cannot
surpass 15%, or the yeast will die.
However, it can also be synthetically produced through two methods.
The first method is the oxidation of ethene. The ethene is gained by the catalytic cracking of
long-chain alkanes, which requires high temperatures (500oC) and a Zeolite catalyst.
The second method is substitution, when a haloalkane reacts with a sodium hydroxide
solution (NaOH) to produce a sodium halide:
Reactions of Alcohols
Primary alcohols can undergo oxidation in two stages to form first aldehydes and then
carboxylic acids. To obtain the aldehyde in the lab, the alcohol is added to a boiling oxidizing
agent. A reflux system (heated reaction under a condenser) is set up so that as soon as the
more volatile aldehyde is formed it distils off and is collected. The same process occurs to
obtain carboxylic acid from the aldehyde, and to turn secondary alcohols into ketones.
Tertiary alcohols cannot be oxidised.
Acidified permanganate (H+/MnO4-) and acidified dichromate (H+/Cr2O72-) are often used as
an oxidizing agent.
Both aldehydes and alcohols are polar, but alcohols can participate in hydrogen bonding in
addition to dipole-dipole forces, so they have higher boiling points. Aldehydes only have
dipole-dipole forces. Carboxylic acids are way less polar.
Alcohols can also undergo dehydration reactions in the presence of a strong acid (such as
sulphuric acid, H2SO4) where the OH group is removed to form water and the alcohol
becomes an alkene. Ethanol can also be dehydrated to Ethene using aluminium oxide
(Al2O3).
Alcohols can be halogenated by an acidic hydrogen halide (e.g. HCl, HBr) or acidified zinc
chloride at high temperatures. The OH group reacts with the acid’s hydrogen to form water
and the halogen attaches to the alcohol to form a haloalkane.
Primary alcohols have the highest boiling points and are most water-soluble because they
have the ‘strongest’ hydrogen bonds (no interference from the carbon chains). In tertiary
alcohols, the 3 carbons around the OH group interfere with its hydrogen bonds.
In dehydration and halogenation, tertiary alcohols are more reactive than secondary and
primary ones! 3o > 2o > 1o
Esters
Wednesday, 19 June 2019
An ester is a combination of an alcohol and a carboxylic acid, with an O=C-O-C functional
group and the suffix ‘-anoate’
The alcohol becomes a methyl group and the carboxylic acid becomes the 'main chain'.
Methanol + Ethanoic acid  Methyl ethanoate.
Pentanol + Butanoic acid  Pentyl butanoate.
The alcohol loses its OH group and the acid loses the H from its OH group. The O connects
the ‘anoate’ and the ‘yl’ groups.
Esterification is an equilibrium reaction. The forward reaction is a condensation/dehydration
reaction, while the reverse is a hydrolysis reaction.
Like all dehydration reactions, the catalyst used is concentrated H2SO4. It occurs at high
temperatures, and hence is performed under reflux. This ensures safety and keeps the
reaction a closed system.
As both products and reactants are extremely flammable/volatile, a naked flame should not
be used.
A fat/lipid is made of several methyl esters with the carbons of the methyl groups
connected. This is known as a triglyceride:
When the esters undergo hydrolysis (anti-esterification), the connected methyl ends
become tri-alkanols (in this case 1,2,3-propantriol a.k.a. glycerol). The ethanoic acid ends
become 'fatty acids', which can be saturated (animal fats) or unsaturated (plant-based oil).
If fatty acids are boiled with strong bases containing Group 1 alkali metals (e.g. NaOH, KOH)
they form soap! This process is called saponification.
When soap encounters Group 2 alkali earth metals (e.g. calcium, magnesium) it forms a
precipitate. This is why true soap doesn't work in 'hard water’ and led to the popularity of
detergents.
Detergents are soaps with ‘greater specificity’ – they are still made up of a non-polar
hydrocarbon chain tail and a polar head, but the head is not an acid group with an attached
alkali metal. It can be made up of various selections of functional groups and can be anionic
(such as sodium sulphate), cationic, or even non-ionic with hydrogen bonds.
Polymers
Tuesday, 25 June 2019
A polymer is a very long molecule made up of a chain of smaller repeating units called
monomers. They make up plastics!
The addition of additives including plasticisers and foaming gases increases the uses of
polymers – for example, turning polystyrene into Styrofoam and making plastics easy to
mould and reshape.
There are two types of polymerisation:
Addition polymerisation requires a radical (molecule with a free electron) and a monomer
that contains a double bond.
The radical is created through the process of initiation.
The radical is attractive to the electrons in the double bond, so the double bond opens up
into two free electrons. One of them attaches to the radical to form a bond, and the other
one remains to make the new radical to attach more monomers. This process is called
propagation, and when it ends this is called termination.
Termination happens because a free radical monomer instead of a double-bonded
monomer attaches to the original radical chain, creating a stable molecule. This can happen
at any point/chain length, so to ensure the maximum chain lengths very few radical
monomers are added to many double-bonded monomers.
As polymers are growing, they can coil around and react with themselves in a process called
backbiting. This causes the chains to be branched, creating substances like Low Density
Polyethylene (LDPE). This is produced at extremely high (>1000 atm) pressures and
temperatures of around 300oC.
To prevent this from happening, an aluminium-based catalyst which holds on to one end of
the chain is added. In the case of polyethylene, this creates High Density Polyethylene
(HDPE) which is much harder and can be produced at only around 2-5 atm and 65oC.
Examples of addition polymers include polyethylene, polystyrene, polyvinyl chloride (polychloroethene) and polytetrafluoroethylene (PTFE or Teflon®).
Polyvinyl chloride (PVC) and polystyrene are very hard due to the ‘chain stiffening’ effect of
their side branches. PVC is also vulnerable to breaking down in UV light.
PTFE is slippery because of the polar C-F bonds which make it stick to itself but resist
bonding with anything else.
Condensation polymerisation is exactly like the condensation reactions previously studied
(e.g. esterification) where two different monomers with complementary function groups
(e.g. carboxylic acid and alcohol) combine, producing a by-product (e.g. water). However, in
order to make a polymer rather than just a new molecule, the monomers must each have
TWO FUNCTION GROUPS (e.g. dicarboxylic acid and di-hydroxyl alcohols) so they can bond
at both ends.
This reaction is used to produce polyesters, but it also occurs in the production of cellulose a plant polymer made of glucose monomers. It is also used to produce nylon and other
polyamines from aminocarboxylic acids.