engleski

DFT study of substituent effects on NMR chemical shifts in 13C NMR spectra of trans-azobenzenes

13C chemical shifts have been determined both experimentally and theoretically (by DFT calculations) for a series of mono-substitueted trans-azobenzenes in para position (X=-F, -Cl, - Br, -I, -CH3, -CH3O, -CN, -NH2 and -(CH3)2N). Geometries were optimized by DFT with the B3LYP hybrid funcional and the 6-311++G** basis set. Nuclear shielding were computed with DFT using GIAO1 method and 6-311++G** basis set. Among the compunds studied, p-bromo and p-iodoazobezene are singled out as possessing hevy atoms (Br, I) and the chemical shifts were also calculated at DFT/cc-pVTZ level of theory with the B3LYP hybrid functional. All calculation were carried out with the Gaussian-98 package. A good correlation is observed between experimental and calculated data. Long-range substituent effects on 13C chemical shifts in mono-substitueted trans-azobenzenes are discussed.

NMR ; DFT ; azobenzene

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