18. How accurate is HyperNMR?

HyperNMR, like almost any simulation method, does not perfectly reproduce reality. However it does represent a significant improvement in accuracy and speed over other wavefunction-based methods for predicting NMR spectra.

We have tabulated some comparisons with experiment for proton and carbon spectra. For proton chemical shifts for 72 molecules (with 143 shifts) we find a standard deviation of 1.1 ppm, with maximum error of 4 ppm. For carbon chemical shifts for 55 molecules (with 118 shifts) we find a standard deviation of 19 ppm. The worst cases are for systems with 3 and 4 membered rings for protons and carbons and allene, furan or pyrrole functional groups for carbon. For systems other than these we expect proton shifts to be within 1 ppm of experiment and carbon shifts to be typically within 5-10 ppm of experiment.

An advantage of HyperNMR is that accuracy can be improved by adding new atom types and associated parameters, and users can do this on their own if they wish. The above results have shown that we need some new carbon atom types and we expect that these will be added to the next release of the program.

If you know of cases where HyperNMR gives poor results for chemical shifts or coupling constants, please send us the HyperNMR file so we can include those cases in the parameterization for future releases of the program.

Please send electronic copies, either by email to support@hyper.com or on floppy disk to Hypercube Inc., 1115 NW 4th Street, Gainesville, FL 32601. Please include an explanation, including values from HyperNMR and experiment, with a reference for the experimental values that you are comparing to.

The program is limited to the first two rows of the periodic table because of the substantial effort needed to derive, implement and test new Slater integral equations for chemical shielding with each higher principle and angular quantum number.

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