Macs in Chemistry

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LSD and CASA added to spectroscopy page


I’ve just added to two applications to the spectroscopy page.

LSD (Logic for Structure Determination) is designed to find all possible molecular structures of an organic compound that are compatible with the experimental spectroscopic data.

Structure building relies on connectivity data found in 2D NMR spectra, without any reference to a chemical shift database. Molecular structures containing up to 50 non-hydrogen atoms were investigated by means of the LSD program. The measurement protocol that is required by LSD includes the recording of 1D 1H and 13C as well as 2D COSY, HSQC and HMBC spectra. The status of each atom must be defined. It includes the atom symbol, the hybridization state (sp3, sp2 or sp), the number of attached hydrogen atoms, and the electric charge. This part of the data set is most often easily deduced by the user from elementary chemical shift knowledge. The status of the heteroatoms is deduced from the elemental molecular formula.

The CASA (Computer-Aided Spectral Assignment) program is intended to assign 13C NMR resonances to the carbon atoms in a user-supplied molecular structure.

It relies on an exploitation of chemical shift correlations in 2D NMR spectra and, optionally, on a comparison between experimental and estimated chemical shift values. The assignment of all resonances is possible if the hypothetic supplied structure is the good one, assuming that CASA input data is correct. CASA may therefore be seen as a 1D/2D NMR-based automatic structure verification tool. The result of the CASA program is a set of lists of possible assignments.

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