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The gauge-including atomic orbital method for calculating 1H and 13C 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-amine-s-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 1H and 13C NMR chemical shifts compare favorably with those reported for atrazine monomer–dimer equilibria in solution. The multiple atrazine N–H 1H chemical shifts correlate with N–H 1H chemical shifts calculated for monomeric atrazine at both the HF and density functional levels of theory. |
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