Computer-assisted structural interpretation of carbon-13 spectral data

Abstract

Computer programs for interpretation and prediction of 13C resonance spectra are described. These programs utilize a data base containing representations of the substructural environments of resonating nucleii together with their chemical shifta. These representations capture both molecular constitution and contiguration, permitting for the first time in a computer program a comprehensive treatment of configurational stereochemical influences on 13C chemical shifts. Substructural features of an unknown structure are derived directly and automatically by '3c interpretive procedures. These features, together with additional structural information, are used to construct structural candidates for the unknown. 13C predictive procedures permit rank ordering of the candidates on the basis of agreement between predicted and observed 'Y! spectra. Applications of these programs to organic structure determination are illustrated through analyses of the structures of some diterpenes.(1) Part

Computer-assisted carbon-13 nuclear magnetic resonance spectrum analysis and structure prediction for the C19-diterpenoid alkaloids

“…Ranges for three-shell environments averaged 1.1 ppm, with the maximum observed range of 7.5 ppm for a class of methines, reflecting continued uncertainty in correct assignments. This class of methines included carbons at C(5), C(9), C (10), and C(13) of the aconitine skeleton. The resonances for these carbons, all of which fall in the same region of the spectrum, show a complex and unpredictable response to substitution of other carbons in the molecule.…”

“…A set of three computer programs which seemed to meet these needs has recently been developed. 10,11 The programs utilize a data base of 13C NMR resonances together with the substructures which characterize the constitutional and configurational stereochemical environment of the resonating carbons. A 13C NMR spectrum is analyzed in the first program by matching the observed resonances to resonances in the data base and retrieving the associated substructures.…”

Computer-Based Structure Determination: Then and Now

“…With few exceptions, − the information input to most spectrum prediction programs relates to connectivity, not to three-dimensional structure. Spectroscopic methods differ in the extent to which spectral properties are influenced by the stereochemistry of the compound.…”

Large Virtual Enhancement of a 13C NMR Database. A Structural Crowning Extrapolation Method Enabling Spectral Data Transfer

“…Its use, restricted to filtering and validating candidate stuctures, proved finally to be inadequate for overcoming the multiple problems intrinsic to the exploration of overextended research spaces. [1][2][3] In contrast to these systems conceived around structure generators, EPIOS (elucidation by progressive intersection of ordered substructures) was developed on the basis of an original modeling of structure/δ 13 C relationships. 4 The priority given right from the beginning to knowledge was expressed by the initial definition of the multi-resonance/ substructure model (MRS).…”