gNMR simulated H-1 and proton-coupled C-13 NMR spectra of substituted 3-nitropyridines. GIAO/DFT calculated values of proton and carbon chemical shifts and coupling constants

Abstract

The magnitude of one bond and long-range coupling constants in 3-nitropyridine 1 and its derivatives 2-16 were determined from the proton-coupled C-13 NMR spectra in CDCl3. The GIAO/DFT (Density Functional Theory/Gauge Including Atomic Orbitals) calculations on B3LYP/6-31 +G(d,p)//6-31G(d) and B3LYP/6-311 + +G(d,p)//6-31G(d) optimized structures of 1-16 were employed for the determination of proton and carbon chemical shifts and coupling constants ((n)J(HH) and (n)J(CH)) and the calculated data compared with the experimental NMR data. The GIAO/DFT calculations, in conjugation with iterative simulations of the proton-coupled C-13 NMR spectra using gNMR software, provide reliable values of (n)J(CNO2,H) couplings, which could not be obtained from the proton-coupled C-13 NMR spectra of 1-16 due to line broadening associated with quadruple relaxation involving the N-14 nuclei and non-zero C-13-N-14 couplings