Theory of electronic structure and nuclear quadrupole interactions in heroin

A first principle investigation has been carried out for the electric field gradient tensor at the ¹⁴N nucleus in heroin (C₂₁H₂₃NO₅) using the Hartree-Fock-Roothaan procedure for determination of the electronic structure employing atomic coordinates based on available X-ray diffraction data. The hydrogen positions were not available from experiment and were determined by energy optimization in our investigations. Our calculated quadrupole coupling constant e²-qQ for ¹⁴N was found to be -4.906 MHz, the magnitude being in good agreement with the corresponding recently available magnitude of 5.3163 MHz from nuclear quadrupole resonance measurements. The value of the asymmetry parameter η was found to be 0.054, the smallness of its size being in agreement with that of the experimental value of 0.028. Possible sources that could further improve the quantitative agreement between theory and experiment are discussed. The quadrupole interaction parameters for the ¹⁷O and ²H nuclei are presented with the hope that experimental values for them will become available in the future, which would allow a comprehensive comparison between theory and experiment for all the nuclei in heroin, enabling a thorough test of the calculated electron distribution in the molecule.