Organic chemistry revision.

Organic chemistry is the study of compounds containing carbon.  the chemical and physical properties of these compounds are determined by their structure and functional groups.

A functional group is part of a molecule that takes part in chemical reactions.  Organic compounds are named according to the type and position of the functional group within their structure.

The types of formulae:

The empirical formula gives the simplest ratio of element atoms to each other.
The molecular formula gives the actual number of element atoms in a molecule.
The structural formula shows the atoms present and all the bonds between them.

Naming organic compounds

Need some revision?  The following website is interactive and gives you some practise naming a range of organic compounds.  The relevant topics: alkanes, alkenes, alkynes, some from organic halides, alcohols, aldehydes, ketones, carboxylic acids and esters.

I summary table is also provided below:

And just for you Hannah, I will include a table to prefixes for naming the carbon backbone:

Carbons 1 2 3 4 5 6 7 8 9 10
Name Meth- Eth- Prop- But- Pent- Hex- Hept- Oct- Non- Dec

Alcohols

Well, we’ve practised naming them (above), so what else do you need to know?

This website gives a good overview and introduction to alcohols.

Classification

  • alcohols can be classified as primary, secondary or tertiary according to the position of the -OH group in the molecule.

Displayed formulae of isomers of pentanol

Oxidation

Alcohols ca be oxidised to produce various products.  The type of alcohol obtained when oxidising an alcohol depends on whether the alcohol is primary or secondary (tertiary alcohols cannot be easily oxidised).

  • primary alcohols react with acidified dichromate to produce an aldehyde, which can further react to form a carboxylic acid.
  • secondary alcohols react with acidified dichromate to produce a ketone.
  • tertiary alcohols do not readily react.

Note: in the examples you will encounter the alcohols are reacted with acidified dichromate, so the formulae H+/Cr2O72-will appear above the arrows.

Fermentation

Ethanol can be produced by the fermentation of glucose.

The conditions required for fermentation to occur:

  • yeast (an enzyme)
  • a warm temperature
  • anaerobic environment (little or no oxygen)
  • slightly acidic
  • dilute aqueous environment

Alkanes, alkenes and alkynes

The number of hydrogen atoms associated with a given carbon chain may vary.  When the chain carries the maximum number of hydrogen atoms possible, the hydrocarbon is said to be “saturated”.  Saturated hydrocarbons are alkanes.  When double or triple bonds are present, the carbon chain no longer has the maximum number of hydrogens bonded for the given amount of carbon atoms, so it is termed “unsaturated”. Unsaturated hydrocarbons are alkenes and alkynes.

Addition reactions for alkenes and alkynes

I tried to find a nice diagrammatical summary of these reactions for you, but this is the best I could get.  In short, double or triple bonds can ‘break open’ and a component can be added to each of the carbon atoms where the bond was originally. 

If you used:

  • Br2, a bromine atom would be added to each of 2 carbon atoms.
  • HCl, a H would be added to one carbon where the double (or triple) bond was, and a Cl would be added to the other carbon.
  • H2 (with a catalyst and pressure), an unsaturated compound could be turned into a saturated compound.
  • H2O, an -OH group could be added to one carbon and a H to another, thus creating an alcohol.

Some of these are shown below:

The most notable one on those mentioned above, would be the addition of Br2 – or bromine water – to an unsaturated hydrocarbon.  This can be used as a test for the presence of a double or triple bond.  This reaction is summarised in the video below:

In short, when bromine water is added to:

  • an unsaturated hydrocarbon (double or triple bonds present), the brown colour will turn colourless.
  • a saturated hydrocarbon (only single bonds present), the solution will remain brown.

Esters

Many esters are sweet smelling substances.  Naming them can be a bit tricky, you have to know both the name of the alcohol and carboxylic acid that it was made from.  Check the link at the top of the post if further details are required.

Preparation

So, we’ve worked out that esters are prepared from an alcohol and a carboxylic acid.  The general reaction equation is shown below:

Note that water is also a product.

A more specific example is shown below:

In this example, methanol is reacted with butanoic acid to produce methyl butanoate and water.

Well, I think that about covers most of what you need to know (not quite as much this time, luckily).  Good luck drama students with your performance tonight.  Good luck chemistry students with your test revision!

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