In this instalment of Docta’s relearning organic chemistry the term “group” will be encountered for the first time. The word group is an umbrella term to describe a structural component of a substance, it is not a substance in it’s own right but a common set of atomic arrangements.
Combining power of molecules
The two great chemists Liebig and Wohler continued there pioneering research into isomers to try and crack the how and why, to find a method of how to distinguished between isomers and at the same time convey the chemical differences between them.
It was evident that an organic substance could not be classified by it’s molecular formula alone when there was so much deviation in chemical properties.
They found however that oxygen, carbon and hydrogen displayed defined and unvarying combining powers.
Even tho some formula’s such as CH3OCH were found in seven separate compounds it was clear that there was not an unlimited number of combinations. Formulae such as CH4O, C2H2O4, C2H2O2, CH2O and C2H6 were found only as single compounds. From theses observations it quickly became apparent that as the quantity of carbon atoms increased the number of isomer combinations increased also.
Experiments by Liebig and Wohler in 1832 on chemical transformation were invaluable in solving the isomer problem.
It was found that groups of atoms remanned unchanged and displayed unity even when passed through multiple levels of chemical transformation (>>).
Benzaldehyde>>Benzoic acid>>Benzoyl chloride>>Benzamide>>Methyl benzoate, each of these compounds was found to contain the atomic arrangement C7H5O, this arrangement came to be known as the Benzoyl group with H, OH, Cl, NH2, or CH3O in the Benz compounds.
Another chemist of the time Gay-Lussac (1778-1850) found the same kind of relationship with the compounds of the Cyanogen group.
The puzzle was finely solved by Kekule (1829-1896) in 1858 with the publication of his theories of structure.
Kekule theorised that the “combining power” or valence as we would say today was static and unchangeable for each of the organic elements, Hydrogen has 1 valence unit, Oxygen 2 units, Nitrogen 3units and Carbon 4 units of valence.
The bond are represented in the graphic formula as straight lines. Along with the new graphic to illustrate valence comes a new vocabulary we now say the carbon-carbon bond or the carbon-hydrogen bond witch in tern can be abbreviated to the C-C bond or the C-H bond.
There also came abbreviations for the groups such as n-Pr for normal-Propyl or Me for the Methyl group. Any combination of graphic, condensed or abbreviated formula can be used to best describe properties and behaviour.
The invention of molecular and structural formulas and the additions made to it over the next hundred or so years made it so that today a compound is better left unnamed if there is any chance of ambiguity. Making organic chemistry a science of universally recognized accuracy.
The organic states
Oxidation, burn baby burn…….
TO BE CONTINUED….
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