GIAO NMR calculations for atrazine and atrazine dimers:: comparison of theoretical and experimental 1H and 13C chemical shifts

The gauge-including atomic orbital method for calculating H-1 and C-13 nuclear magnetic shielding tensors at both the Hartree-Fock (HF) and density functional levels of theory is applied to atrazine (2-chloro-4-ethylamino-6-isopropyl-amines-triazine) and atrazine dimers. Atrazine calculations include the HF/6-31G*, HF/6-31G**, and HF/6-311+G(d,p) basis sets. Atrazine density functional calculations (DFT) use the B3LYP and B3PW91 methods and the 6-31G*, 6-31G**, and 6-311+G(d,p) basis sets. Hartree-Fock atrazine dimer calculations include the 6-31G* and 6-31G** basis sets. Atrazine dimer B3LYP calculations are reported for B3LYP/6-31G* and B3LYP/6-31G*//B3LYP/6-31G**. The H-1 and C-13 NMR chemical shifts compare favorably with those reported for atrazine monomer-dimer equilibria in solution. The multiple atrazine N-H H-1 chemical shifts correlate with N-H H-1 chemical shifts calculated for monomeric atrazine at both the HF and density functional levels of theory. (C) 2002 Elsevier Science B.V. All rights reserved.