Organic compound identification.

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A Level Chemistry Practical

        

ORGANIC COMPOUND IDENTIFICATION

The reason to carry out different chemical test on the unknown six organic compounds is to find their structure and identity. The unknown compounds are labeled as compounds A  F respectively. We are provided with the information that tells us the sort of different chemical tests that have to be performed on the compounds and we are provided with the technique to carry out these chemical tests. We are given the composition of each compound so we know what are the elements that are in the compounds and what ratio are they in.  Along with the composition data we are also provided with different sorts of other data that will make our task easier and much more bearable. For e.g. we are provided with Mass spectrum in some cases while having the infrared and NMR spectrum in the other along with other tidbits of information specific to each compound.      

Along with carrying out the chemical tests and coming up with the identity of the compounds we are also expected to answer different questions about them. Like for example we are asked to write down the chemical equations in some cases of the chemical test that we are carrying out and in some cases the mass concentrations and molarity.

I am also provided with Chemical test and Inferences. I have been given two tables and there titles and brief description is as follows:

  • The first table is titled Solubility in water and pH of resultant solution in this table I am told what the possible compound type in after checking its solubility in water and testing the pH of the solution.
  • The second table I have been provided with is titled Other Chemical tests, in this table I haven been given different chemical tests and their observations to come up with the most likely suspects of what the compounds were initially.

All this information and given guidance should be enough for me to identify the unknown compounds and draw their structure if possible.

Compound A

Composition:        C = 60.0%

                        H = 13.3%                hence E.F. =          C3H8O

                        O = 26.7%

A simplified mass spectrum of Compound A was given. We were asked to note down the Mr of the compound by observing the spectrum and its molecular formula. We were also asked to, from the spectrum suggest which fragment ions are responsible for the signals at m/z = 45 and 43.

Mr of A =            60                M.F. =               C3H8O

Signal at (m/z) 43 =                [C3H7]+

Signal at (m/z) 45 =                [C2H5O]+

After looking at the infra red spectrum of compound A provided the following bond vibrations are responsible for the signal at:

  • 3370cm-1        =        O – H stretch in Alcohol

  • 2950cm-1        =        C – H stretch in Compound

  • 1125cm-1        =        C – O stretch in Secondary Alcohol

The infra red and the mass spectrum data both have told us that the unknown compound is a secondary alcohol; further chemical tests will reveal the real identity.

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Chemical Tests

  1. Mix 1 – 2 cm3 of A with about 5 cm3 of tap water. Test the pH of the mixture with a few drops of Universal Indicator. Record your observation(s) and conclusion.

  1. In the fume cupboard, add a small spatula measure of solid PCl5 to 1 – 2 cm3 of A. Test any gas evolved with the stopper from a concentrated ammonia bottle. Record your observation(s) and conclusion.

  1. Warm about 1 cm3 of A with 2 cm3 of an equal mixture of potassium dichromate and 2M sulphuric acid in a boiling ...

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