Chapter 20 – Infographic descriptions

20.2a A Brief Guide to Types of Organic Chemistry Formulae

Infographic of a guide to formulae in organic chemistry.

• Molecular formula: The molecular formula of an organic compound simply shows the number of each type of atom present. It tells you nothing about the bonding within the compound. Example:  [latex]C_{4}H_{8}O_{2}[/latex] .
• Empirical formula: The empirical formula of an organic compound gives the simplest possible whole number ratio of the different types of atoms within the compound. Example:  [latex]C_{2}H_{4}O[/latex].
• Condensed formula: In condensed formulae, each formulae atom is listed separately, with atoms attached to it following. In cyclic parts of molecules, like benzene, carbons are grouped.
• Displayed formula: A displaced formula shows all of the atoms and all of the bonds present in an organic compound. The bonds are represented as lines.
• Structural formula: Similar to displayed formula; not all bonds are shown, although all atoms are still indicated using script numbers. Carbon hydrogen bonds are often simplified.
• Skeletal formula: In skeletal formulae, most hydrogen atoms are omitted. Line ends or vertices represent carbon. Functional groups and atoms other than carbon or hydrogen are still shown.

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20.3a A Brief Guide to Types of Isomerism in Organic Chemistry

Infographic about the types of isomerism in organic chemistry.

A guide to the five main types of isomerism that can be exhibited by organic compounds. An isomer of a molecule is a molecule with the same molecular formula but a different structural or spatial arrangement of atoms. This variation can lead to a difference in physical or chemical properties.

Structural isomerism:

• Chain: different arrangement of molecule’s carbon skeleton. The position of the carbon atoms in the molecule can be rearranged to give ‘branched’ carbon chains coming off the main chain. The name of the molecule changes to reflect this, but the molecular formula is still the same. Examples: Butane, 2-Methyl propane.
• Position: The differing position of the same functional group in the molecule. The molecular formula remains the same; the type of functional group also remains the same, but its position in the molecule changes. The name of the molecule changes to reflect the new position of the functional group. Examples: But-2-ene, But-1-ene.
• Functional: Differing positions of atoms give a different functional group. Also referred to as functional group isomerism, these isomers have the same molecular formula but the atoms are rearranged to five a different functional group. The name of the molecule changes to reflect the new functional group. Examples: But-2-ene, Cyclobutane.

Stereoisomerism:

• Geometric: Different substituents around a bond with restricted rotation. Commonly exhibited by alkenes, the presence of two different substituents on both carbon atoms at wither end of the double bond can give rise to two different, non-superimposable isomers due to the restricted rotation of the bond. Examples: (E)-1,2-Dicholorethene ,  (Z)-1,2-Dichloroethene.
• Optical: Non-superimposable mirror images of the same molecule. Optical isomers differ by the placement of different substituents, around one or more atoms in a molecule. Different arrangements of these substituents can be impossible to superimpose – these are optical isomers.

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20.3b A Basic Guide to Decoding Organic Compound Names

Infographic of basic guide to decoding organic compound names. The names of organic molecules can be long and look lie a confusing mix of words and numbers. However, they follow a particular set of rules which allows their structure to be decoded from their name.

• Organic compound representation: Organic molecules are usually represented using skeletal formula. In these diagrams, the line ends and vertices represent carbon atoms. Hydrogen atoms are ‘implied’ – that is, they are not usually shown, but each carbon must have four bonds, and it’s assumed they have the required number of hydrogens for this to be the case. Atoms other than carbon or hydrogen are always shown, and hydrogen atoms are shown if they are bonded to one of these ‘heteroatoms’.
• Functional groups: A molecule’s functional group is the group of atoms that give it its chemical properties and reactivity. It’s usually indicated by a suffix at the end of the name, with a number indicating its position if this is required for clarity. There are many different functional groups. Different functional groups have different suffixes. Examples of funcitonal groups: Alchohols (-ol) e.g. ethanol, aldehydes (-al) e.g. ethanal, ketones (-one) e.g. propane, and amine (-amine) e.g. ethanamine.
• Bond types: Carbon atoms can be lined by single bonds, double bonds, or even triple bonds. The name of the molecules reflects the bonds present.
  

  Types of molecule bonds

  Phrase present in the name	Type of molecule bond present
  -an-	molecule contains only single bonds.
  -en-	molecule contains at least 1 double bond.
  -yn-	molecule contains at least 1 triple bond.
  Double or triple bonds	numbers indicate their position.

• Parent chain: Part of the organic molecule’s name denotes how many carbons make up its ‘parent chain’. This is defined as the longest continuously connected chain of carbon atoms including the functional group in the molecule. Carbons not included are dealt with as ‘side chains’. Examples: Butane, Hexane.

• Side chains: Molecules can have one or more carbons that aren’t part of the parent chain, referred to as a ‘side chain’. The number of carbons in the side chain is used to name it, in the same way as for the parent chain, but the ending -yl is then added. A number is added to show the location of the side chain on the parent chain. If there is more than one of the same side chain at different points, the prefixes di- (2), tri- (3), or tetra- (4) are used in the name. Examples: 2-Methylbutane, 3-Methylpentane, 2-4-Dimethylpentane, 4-Ethylnonan-1-Ol, 3,5,7-Trimethyldecane.
• Stereoisomerism: Chemical names sometimes contain a letter in brackets; for examples, (Z), (E), (R), or (S). These refer to stereoisomerism: when a molecules has the same chemical formula as another, but a different arrangement in 3D space. This can be due to a different arrangement of atoms around a double fond, or when a molecule has two different arrangements of four different groups of atoms around a central carbon which are non-superimposable mirror images.

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20.6a The Chemistry of Petrol & The Tetraethyl Lead Story

Petrol and diesel are obtained by fractional distillation of crude oil. Diesel is removed from crude oil at a higher boiling point, and contains a larger amount of energy per litre, meaning more miles can be covered with the same volume of fuel. Petrol: 35-200 degree Celsius, 5-12 carbons, and 33,7 megajoules per litre. Diesel: 250-300 degrees Celsius, 10-15 carbons, 36.9 megajoules per litre.

In the engine, a mixture of air and fuels is compressed and burned. Combustion forces the piston down, then the piston pushes back up to expel exhaust gases and the cycle begins again. In diesel engines, the fuel is injected after the air has been compressed before combustion.

Engine knocking happens when the combustion of the fuel doesn’t occur in sync with the engine cycle, causing lower engine efficiency and engine damage. Octane ratings measure how well fuel avoids this problem; higher values indicate less knocking. Isooctane and n-heptane are refences.

Compounds added to petrol to boost octane rating: Tetraethyl lead, was banned in most countries due to releasing toxic lead fumes. Anti-knocking agents used in unleaded petrol: methyl tertiary-butyl ether (MTBE), ethanol, benzene, and toluene.

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20.6b Today in Chemistry History: Susan Solomon, ozone depletion, and CFCs

Susan Solomon was born in 1956. They provided first direct evidence of chlorine compounds breaking down ozone. Solomon’s work confirmed that ozone could react with chlorofluorocarbons on the surface of polar stratospheric clouds. Her work informed the Montreal Protocol, legislation which regulates chemicals that damage the ozone layer.

Ozone and Chlorofluorocarbons: In the stratosphere, CFCs are broken down by UV radiation, releasing highly reactive chlorine radicals. These reacts with and break down ozone molecules. The chlorine radicals are regenerated, so they can go on the to react with thousands of ozone molecules.

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Attribution & References

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