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Organic Chemistry

Important Notes

This page is intended to give simple notes on organic chemistry.  For detailed information please consult reputable references and/or use the links provided at the foot of the page.
The structures I have used are based on lewis dot structures.  These structures do not provide clear 3D geometric information of the molecules and sometimes may provide misleading information on the relative positions of the bonds.


Organic Chemistry

The branch of chemistry that is concerned with compounds of carbon.   Therefore this deals with living matter, oil products, plastics etc etc.   Because of the extraordinary bonding properties of carbon there are many more organic compounds than inorganic compounds

Until the early 1800's chemical substances relating to living matter were called "organic" materials and were considered fundamentally different to other substances, mainly of mineral based, which were called inorganic substances.  It was considered a "vital force" was necessary to form living (organic) matter.  In 1828 this theory was discredited by Wohler but the term organic has remained.

Most organic substances contain Hydrogen(H) and Carbon(C) and many contain Oxygen(O), Nitrogen, Sulphur (S), Phosphorous (P)and the Halogens Flourine(F), Bromine(Br), Chlorine(Cl) and Iodine(I).   These and other elements are normally bonded to carbon by covalent bonds as opposed to ionic bonds which are typical of inorganic compounds.

The covalent bonds which are relatively weak compared to the ionic bond.  Therefore organic compounds typically have low critical temperatures...

The Pauling electronegativity value for carbon of 2,5 is approximately in the middle of the scale (0,8 to 4,0) covered by all elements. ref electronegativity values )  This number provides a measure of the bonding characteristic.  Carbon being in the middle of the range will for the majority of cases combine with other elements with covalent bonds.  In these bonds the electrons will not be attracted to of from either or the bonded atoms to any great extent.

Organic Chemistry Families

The total field of organic chemistry is so large that it is necessary to break it down into sub-groups or families of compounds .
Some of these "families are identified below-with links to relevant notes

  • Alkanes (all single bonds)
  • Alkyl Halides (involving at least one halogen bonded to a carbon)
  • Alkenes (one or more Carbon - Carbon double bond
  • Alkynes (one or more Carbon- Carbon triple bond)
  • Aromatic Compounds (involving the molecule Benzene, Napthalene, Anthracene, etc)
  • Alcohols (one or more OH group)
  • Thiols (similar to alcohols except Sulfur (SH) instead of Oxygen
  • Ethers (one or more Oxygen single bonded to two carbons)
  • Thioethers(similar to ethers except a Sulfur atom in place of an Oxygen atom)
  • Aldehydes (one or more formyl group -CH=O)
  • Ketones (one or more keto group C=O)
  • Carboxylic Acids (at least one carboxyl group -COOH)
  • Esters ( Formed by reactions with acids and alcohols)
  • Amines (one or more Nitrogen bonded to Hydrogen or carbon atoms)
  • Amino Acids (one or more amino group NH2 and one carboxyl group -COOH)
  • Carbohydrates ( several OH groups and a formyl or keto group)
  • Organometallics (with ionic bonding between a metal and a carbon structure)





Naming Organic Chemicals

The IUPAC (The international Union of Pure and Applied Chemistry) has produced an accepted naming convention (systematic Nomenclature) for chemicals.. The name includes

  • a prefix, which describes the substituent
  • a stem , which describes the longest chain
  • a suffix , which describes the compound type

A simple molecule illustrating the naming convention is shown below






Aliphatic Compounds

An aliphatic compound is any chemical compound belonging to the organic class in which the atoms are not linked together to form a ring.   A major structural groups of organic molecules, the aliphatic compounds include the alkanes, alkenes, and alkynes, and substances derived from them, by replacing one or more hydrogen atoms by atoms of other elements or groups of atoms.





Alkanes (paraffins)

These saturated hydrocarbons with the general formula CnHn+2.    All of these substances end with -ane(the IUPAC suffix) and include those listed below.   The stem names relate to the number of carbon atoms in the molecules as shown below

  • 1 Carbon atom - meth
  • 2 Carbon atom - eth
  • 3 Carbon atom - prop
  • 4 Carbon atom - but
  • 5 Carbon atom - pent
  • 6 Carbon atom - hex
  • 7 Carbon atom - hept

etc.etc.

There is no IUPAC prefix for the alkanes as described here.

The lower members of the series are gases and the higher molecular weight alkanes are waxy solids.  Alkanes are obtained from natural gas and petroleum.

Note; A methyl group is simply CH3.The straight alkane chains are formed by the successive replacement of the end hydrogen atom by a methyl group as shown below...

Methane (CH4)......

Ethane (C2H6)......

Propane (C3H8)......

Butane (C4H10)......

Pentane (C5H12)......

Hexhane (C6H14)......

Heptane (C7H16)......

etc. etc.




Alkyl Halides (Haloalkanes)

These are organic compounds in which more one or more hydrogen atoms of the alkane series have been replaced by halogen atoms(atoms with one electron short of stable structure )..Example are chloromethane CH3Cl, Dibromethane CH2BrCH2Br etc.   These can be formed by direct radiation between the constituent substances with ultravoilet light..








Alkenes

These are unsaturated hydrocarbons that contain at least one double carbon bond.   The general formula for alkenes with only one double bond in the molecule is CnH2n where n is the number of carbon atoms in the molecule.

The double bond between two carbon atoms is not twice as strong, -the second bond formed between the carbon atoms is weaker than the first.   Thus, the second bond is more vulnerable to attack by suitable reagents, even under fairly mild conditions.   The reactions of this second bond tend to be addition reactions causing the unsaturated carbon atoms become saturated.   The alkenes are therefore more reactive than alkanes.

The alkenes are highly flammable and burn readily in air, forming carbon dioxide and water,. For example, ethene burns as follows :

C2H4 + 3 O2 ==> 2 CO2 + 2 H2O

The first three alkenes are gases, the intermediate alkenes are liquids and higher members of the olefin series are wax like solids at room temperature.    The alkenes are insoluble in water, but are soluble in organic solvents.   The liquids and solids have a density less than water.






Alkynes

These are unsaturated hydrocarbons that contain at least one triple carbon bond.

The names of all alkynes end in "-yne".      In the case of higher members of the alkene series, the triple bond may be between the terminal carbon atoms of the chain, or may be between internal carbon atoms in the chain.
.
Alkyne properties
Alkynes are compounds which have low polarity, and have physical properties that are similar to those of the alkanes and alkenes.

  • They are insoluble in water.
  • They are quite soluble in the usual organic solvents of low polarity .
  • They are less dense than water.
  • Their boiling points show the usual increase with increasing carbon number.
  • They are very nearly the same as the boiling points of alkanes or alkenes with the same carbon skeletons.

Lewis structures for two alkynes are shown below..






Aromatic Compounds

Aromatic Compounds

Aromatic compounds are a major class of chemical compounds whose molecular structure includes one or more planar rings of atoms joined by covalent bonds of two different kinds.   The term aromatic was first used in 1860 for a group of hydrocarbons isolated from coal tar and characterised by their strong odours. In chemistry, aromaticity has come to denote the chemical behaviour of this class of molecules.

An aromatic is a organic compound that contains a benzene ring in is molecule or has very similar chemical properties to benzene.  Aromatic compounds are unsaturated yet they do easily complete addition reactions.

Benzene comprises a hexagonal ring of carbon atoms possible lewis structures are shown below.   However in practice the carbon-carbon bonds would not be double and single..they would be would be bonds intermediate between double and single...






Alcohols (at least one OH group)

All alcohol compounds end with ..ol e.g. methanol, ethanol.

Primary alcohols have two hydrogen atoms on the carbon joined to the -OH groups.   Secondary alcohols have only one hydrogen atom on the carbon joined to the OH group.   Tertiary alcohols have no hydrogen atoms on the carbon attached to the -OH molecule.


For example
The ethanol formula can be written CH3 CH2OH
this is a primary alcohol.

The 2- propanol molecule can be written as shown below..This is a secondary alcohol



The molecule "2-methylpropan-ol" can be written as shown below..This is a tertiary alcohol




Thiols (similar to alcohols except Sulfur (SH) instead of Oxygen

Note: Thio -> sulphur containing

Thiols have an older name "mercaptan" . This relates to their ability to react with mercury.  They are named according to the hydrocarbon e.g ethane thiol C2H5SH.

These chemicals generally have a strong odour.  They are, unlike alcohols strongly acidic forming saltlike substances when reacting with metals and alkalis.




Ethers (at least one Oxygen single bonded to two carbons)

These are usually liquids with pleasant odour , but some aromatic and the higher aliphatic ethers are crystalline solids.   They are insoluable in water but soluble in alcohol and diethyl ether.  The commonest ether diethyl ether is usually simply called ether.  Diethyl ether (ethoxyethene) is an anaesthetic and a very useful organic solvent

These compounds are volatile and highly flammable.

The ethers are made by dehydrating alcohols using sulphuric acid.




Thioethers- Sulphides (similar to ethers except a Sulfur atom in place of an Oxygen atom)

Thio 0> Suphur containing..
Thioethers are organic compounds containing the group -S- linked to two hydrocarbon groups.   The thioethers are named according to the linked organic molecules.   The organics molecules identified in alphabetic order see examples below.

These compounds are generally more reactive than the related ethers.





Aldehydes (at least one formyl group -CH=O)

These are organic compound containing the group as shown below attached directly onto another carbon atom.

Methanal (formaldahyde) HCHO is a member of this group although it is not a typical aldehyde.   Aledehydes are normally colourless liquids (aliphatic) or solids ((higher aromatics) with characteristic colours.   These compounds are oxidized to acids and reduced to primary alcohols.

Aldehydes are formed by oxidation of primary alcohols.





Ketones (at least on keto group C=O)

Chemistry naming conventions always end this range of chemicals with -one Where Aldehydes have the C=O group (carbonyl) on an end carbon atom Ketones have it on a middle carbon atom. Secondary alcohols can be oxidixed into ketones.

Acetone (propanone) as shown below is the simplest ketone.  It is made by the oxidation of propan-2-ol .   It is a solvent and is used in the manufacture of plastics.




Carboxylic Acids (at least one carboxyl group -COOH))

These include at least one carboxyl group -COOH as shown below

Typical carboxylic acids include methanoic (formic) acid (HCOOH->HCO2H), ethanoic acid-acetic acid (CH3COOH), butanoic acid (CH3CH2CH2COOH ).   Because carboxylic acids have both a lone oxygen and an OH group, they are strongly hydrogen-bonded to each other, therefore having high boiling points.
Because a large number of carboxylic acids occur naturally in fats and oils these are therefore also known as "fatty acids". The carboxyl group is weakly acidic and all carboxylic acids neutralize OH-.




Esters

Esters are organic compounds formed by reactions between alcohols and acids .  Esters containing simple hydrocarbon groups are volatile fragrant substances used as flavourings in the food industry.   In esters one of the oxygens has a double bond the other oxygen atom is bonded to a carbon atom of a hydrocarbon.   >/p>




Amines (at least one Nitrogen bonded to Hydrogen or carbon atoms)

These organic compounds are produced by replacing one or more of the hydrogen atoms in ammonia with an organic group.

Amines are classified as primary, secondary, or tertiary depending on whether one, two, or three of the hydrogen atoms of ammonia have been replaced by organic groups.   Diamines, triamines, and polyamines contain two, three, or more nitrogen groupings of the types identified.

Amines are alkaline to various levels of intensity.   Amines can be aliphatic or aromatic in nature..

Aniline, ethanolamines, and numerous other amines are major industrial chemicals used in making rubber, dyes, pharmaceuticals, and synthetic resins and fibres and in a host of other applications.

The lower molecular weight amines have a fishy-putrid odour.  The aliphatic amines have densities 600 to 800 kg/m3 and aromatic amines have densities about + 1000kg/m3.




Amino Acids (at least one amino group NH2 and one carboxyl group -COOH)


A large group of organic compounds containing both the carboxyl group COOH and the amino group NH2.  These include Glycine H2NCH2COOH.  Many proteins are built up entirely of amino acid groupings by condensation between the NH2 and COOH groups.
The amino acids are colourless, crystalline substances which melt with decomposition.  They are mostly soluble in water and insoluble in alcohol.

The two simplest amino acids are shown below:...




Carbohydrates (at least several OH groups and a formyl or keto group)

A group of organic compounds based on the general formula C x(H 2O) y.   The simplest carbohydrates include sugars (saccharides)including glucose and sucrose.

Carbohydrates perform vital roles in living organisms .  Sugars, including glucose, and their derivatives are essential intermediates in the conversion of food to energy.   Starch and other saccharides serve as energy stores in plants.....




Organometallics (with an ionic bonding between a metal and a carbon structure)

These are compounds in which metals ions or atoms are bound to organic groups via a carbon to metal bond. These may have single metal to carbon bonds as in Aluminium Alkyls (Al(CH3)3.   The compounds can also be more complicated double bonds...

A more precise description is "Organometallics relates to compounds in which an organics group is attached through carbon to an atom which is less electronegative than carbon."

Organometallics predates organic chemistry and is now one of the largest forms of chemistry mainly in the petrochemical industry.   This chemistry breaks down the barriers between organic and inorganic chemistry.

It is recommended that further reference on this topic is made to Organometallics


Links relevant to organic chemistry..
  1. Virtual textbook of organic chemistry....Essential link for learning about organic chemistry
  2. Alkenes Chemical Properties... Useful detailed notes
  3. Organic Chemistry Online... Very useful tutorials for students
  4. Organic Mechanisms Menu... Mechanism for various organic reactions
  5. AP Chemistry -Study Cards... A set of chemistry study cards- Ideal look up revision aids
  6. Organometallics... A very professional website devoted to organometallics

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Last Updated 28/01/2013