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For example, how did they determine using evidence that when 2-chloropropane reacted with ethoxide, a strong base, formed propene as the major product and 2-ethoxypropane as the minor product?

Could someone explain how did chemists determine the major products without NMR Spectroscopy? I have no lab experience and do not have access to them either.

Anonymous
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  • there's also https://chemistry.stackexchange.com/questions/54381/how-to-determine-the-structure-of-organic-molecules-without-spectroscopy – Mithoron May 21 '17 at 21:42
  • I am not familiar with how a degradation reaction is done. I know this is a forum for professional chemists and those who have studied it at a university, but for me the only chemistry course I've taken was in high school. Elaborate if you can – Anonymous May 21 '17 at 21:48
  • After 11 questions you still dunno it's not forum for chemists but Q&A site for everyone? BTW what degradation? – Mithoron May 21 '17 at 22:24

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In absence of currently available (or, in principle available) spectroscopies like NMR, IR, Raman, UV-Vis; and mass spectrometry our ancestors tried first to separate the products obtained by sequential recrystallisation. Or by extraction under acidic, neutral, basic conditions (including back extraction).

They then recorded other physical properties of the purified products, if accessible, which then were compared with reference data. For example, melting point and crystal shape if the products were solid, otherwise boiling point, refractive indices of the products obtained. Then, they knew a whole array of pretests to check for the presence / absence of elements in the products formed, like Beilstein test for halogens and Lasaigne test for nitrogen. They would determine the molecular weight by means of cryoscopy or ebullioscopy.

From a chemical point of view, it was common to subject the products to combustion analysis to determine the molecular formula. (One of the instruments for this, the Kaliapparat is still present in the logo of The American Chemical Society.) Till today, there are journals preferring this over a mass spectroscopic determination of the molecular weight.

They knew about reactions that would yield derivatives, for example from the reaction with picric acid (affording pircrates), or with toluenesulfonic acid (yielding amides); often crystalline with a sharp melting point, easing to compare with reference data. If not, other reactions like the haloform reaction would sequentially degrade the products into fragments, and then these products obtained would be characterised by physical or chemical means.

And obviously, the balance was much more "sacred" than today, where often we "just" weight-in reactants, and weight-out products.

Buttonwood
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