Simulation of carbon-13 nuclear magnetic resonance spectra of substituted cyclopentanes and cyclopentanols

Simulation of carbon-13 nuclear magnetic resonance spectra of linear cyclic aromatic compounds

“…Four approaches can be used to simulate or model chemical shifts in aromatic compounds; (1) the direct calculation of chemical shifts based on the theoretical principles of magnetic shielding (1-8), (2) the calculation of chemical shifts based on substituent effects (9), (3) the derivation of empirical models that relate structural characteristics to chemical shifts (10)(11)(12)(13)(14)(15)(16)(17)(18), and (4) the retrieval of chemical shifts from a spectral database in which each stored chemical shift is indexed to an encoded representation of the corresponding carbon atom environment (19). Each of these methods has limitations.…”

“…The techniques that rely on the detection of particular amino acids, such as UV absorbance or fluorescence of the amino acids phenylalanine, tyrosine, and tryptophan (11), or electrochemistry of cysteine (12), tyrosine, and tryptophan (13,14), lack generality. Procedures that use amine-specific chemistry for derivative formation, such as ninhydrin (15,16), and fluorescamine (8, 17, 18), lack specificity. In addition, the amine derivatizing procedures are blind to peptides that lack an amino terminus, such as those that contain pyroglutamate or those that are formylated.…”

Automated model selection for the simulation of carbon-13 nuclear magnetic resonance spectra of cyclopentanones and cycloheptanones

“…13C NMR chemical shifts are highly dependent on geometry. For example, in cyclopentanones and cycloheptanones, the chemical shift of a particular atom can vary up to 8 ppm depending on whether it exists in a cis or trans isomer. Topological and electronic descriptors alone cannot encode differences in geometry such as axial and equatorial attachments or cis and trans isomerism.…”

“…The creation of a spectral simulation database containing predictive equations for prior simulation studies was recently reported (3). Prior to this study, the database consisted of 66 regression models capable of simulating 13C NMR spectra of linear and branched alkanes (4), cycloalkanes (5), cyclohexanols and decalols (6), hydroxysteroids (7), cyclopentanes and cyclopentanols (8), norbornanols (9), cyclohexanones and decalones (10), piperidines (11), polychlorinated biphenyls (12), alkyl-substituted benzenes and polyaromatics (13), ketosteroids (3), and quinolines and isoquinolines (14). A complete summary of the current model database is shown in supplemental material Table VII.…”

“…Previous reports from this laboratory described imaging of surfaces by employing the feedback 1 Current address: Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125. mode, where the steady-state tip current, iT, controlled by an electrochemical reaction at the tip electrode, is a function of the solution composition, tip-substrate distance, d, and the nature of the substrate itself. The measurement of ¿r can thus provide information about the topography of the sample surface as well as its electrical and chemical properties; electrodes (e.g., minigrids and interdigitated electrode arrays) (6)(7)(8), polymer and oxide films on electrode (7,9), and biological materials (10) have been imaged. Thus SECM allows, at least in favorable circumstances, analysis of surface features with high spatial resolution.…”