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Logic Puzzle #15: Multiple Molecular Formulae … Solution

May 5, 2011

An effective elucidator is capable of connecting information from multiple sources with the goal of eliminating the inconsistent candidates. In this puzzle, the candidates are molecular formulae (MFs).

The previous blog listed 4 potential MFs differing in mass difference and RDBE. The mass difference is not a good filter as the mass differences for the four MFs all fall within the listed error tolerance of 0.5 Da. The next step is to examine the 1H NMR spectrum and tie this with the differing RDBE values.

If all the signals on the 1H NMR spectrum are aromatic CH groups, then the minimum value for the RDBE is 4, that is, a single mono-substituted phenyl ring is present. If all the signals pertain to an acyclic alkene, then the minimum value for the RDBE is 2. The likelihood for all the alkene signals to overlap at ~7.15 ppm is very low and thus for simplicity’s sake this scenario can be ignored. If there is a mixture of the two substituents, then the minimum value for RDBE is 5.

Based on the scenarios listed above, and assuming no contribution of exchangeable protons to the integral on the 1H NMR spectrum, the MFs can be dwindled down by eliminating C16H28O10 and C17H32O9.

Thanks Walter for your comment.


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