100 Year Old Pyridiniumsalts - An Easy Job for NMRPredict !

There was a debate on the synthesis of 1,7-Diaza[12]annulene-derivatives, which were shown to be N-substituted pyridiniumchlorides by Professor Manfred Christl from University of Würzburg. The details including all the literature references can be found in the article 'Angew.Chem., 2007, 119, 9312-9313' written by M. Christl. One of the points which was discussed by Professor Christl was the system of peer-reviewing. On the WEB there is also an ongoing discussion on the implementation of 'robot-referees', which are capable to check analytical data (see for example Peter Murray-Rust's weblog).

As I always clearly stated on Peter's weblog, we have already these 'robot-referees' in NMR-spectroscopy, because we are in the lucky situation that sophisticated algorithms for spectrum prediction and spectral similarity searches are available. There is always the discussion on 'Open Access' to analytical(spectral) data - I have also shown that e.g. spectrum prediction costs the incredible amount of 1.7 Eurocent per prediction, when using 'NMRPredict Online Full' with 345,000 C-NMR spectra as knowledge base. An amount of money neglectible when comparing to the total costs of a paper on organic synthesis.

I had the honor to get the C-NMR spectral data from Org.Lett.,2006,8,4279 for my investigation (they are NOT furthermore available online !)

The central question was: Is it possible to recognize that exactly the same C-NMR data as published in Org.Lett. have been already assigned to different structures, namely the corresponding pyridiniumchlorides ?

Technology used:

The result is:

Simply type in your lines - press the 'SEARCH'-button and get the information, that exactly these C-NMR spectra have been already published in 1980 by A. Lycka.

When using the C-NMR data of compound #3b the N-substituted pyridiniumchloride is on position #1 after ranking of 134 possible answers:

Compound #3b

When using the NMR-data of compound #3d, 2 answers are found on positions 2 and 6 (chlor- and bromo-derivative respectively)

Compound 3D

Compound 3D

Starting from the C-NMR data of 3f leads directly to the correct solution:

Compound 3f


Page written by: Wolfgang.Robien(-at-)c13nmr.at
Page written on: January 31st, 2008
Page online since: January 31st, 2008