The CH3 groups of an isopropyl moiety are magnetically equivalent (isochronous) except in chiral environments. Our students synthesize an isopropyl oxazolidine to illustrate this [J Chem Educ 2007  , 84, 1011-13]. Spartan'10 or Gaussian 09 molecular modeling software give the correct assignment of CH3 signals while ChemNMR spectral predicting software does not. In another assigned experiment our students reduce benzoin to hydrobenzoin and make an acetonide to establish the stereochemistry of their product [J Chem Educ 1983  , 60, 1084-5]. The appearance of non-equivalent CH3 groups in NMR spectra of the resulting acetonide allow students to state unequivocally that they obtained the meso isomer. Again, ChemNMR provides contradictory results while quantum mechanical calculations using Spartan and Gaussian are in agreement with what is observed experimentally. This problem recurs throughout the organic chem course. We have thus moved to make quantum mechanical calculations available to our students. Supported in part by a Faculty research grant and one from NSF for a 300 MHz NMR spectrometer.

Assigning 13C NMR chemical shifts of methyl groups of an isopropyl moiety in chiral environments

246th National Meeting (2013)

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