Establishment of molecular formula of organic compounds from ir and nmr
spectra: a new approach based on the expert system application
M.E. Elyashberg (ACD/Labs) , Yu.Z. Karasev and E.R.Martirosian
All-Russian Research Institute of Organic Synthesis, Radio St. 12, 107005
Moscow, Russia
The main task of qualitative organic analysis is known to be the
determination of the chemical composition and the structure of an unknown compound. There
exist expert systems intended for the molecular structure elucidation (X-PERT
[1], for instance and ACD/Structure Elucidator), while the molecular formula
(MF) being considered as an independently determined item of initial data. In
this report, we have shown that the expert system itself can be used as a new
tool for the molecular composition determination.
The approach takes into account the fact that the information about the
chemical composition and structural formula of a substance is "smeared out"
over spectra of different origin, while there exists a relationship between
the chemical composition, structure and spectra. The problem solving is
transferred into the space of structural isomers, the families of which can be generated,
in principle, from given molecular formulae fitting into the molecular masses.
This also makes it possible to derive equations which allows one to evaluate
quantitatively the amount of structural information carried by the molecular
mass and molecular formula. Fairly frequently isomer structures are shown to
have IR and NMR spectra, in some sense, rather characteristic for their
molecular formulae. This dependence was used for spectral filtering the
molecular formulae generated from a given molecular mass. The X-PERT and
ACD/Structure Elucidation applications combined with a program for 13C NMR
prediction allows one to carry out all main operations necessary for choosing
the most probable MF and the molecular structure. Examples illustrating the
features of the approach suggested will be given.
1. M.E.Elyashberg, E.R.Martirosian, Yu.Z.Karasev, H.Thiele, H.Somberg. Anal.
Chim. Acta., 337 (1997) 265; 348 (1997) 443
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