17723-18-1Relevant articles and documents
Perfluoro Effects in 15N Nuclear Magnetic Resonance Spectroscopy. Part 1. Aryl and N-Heteroaryl Azides
Kanjia, D. Magan,Mason, Joan,Stenhouse, Ian A.,Banks, Ronald E.,Venayak, Narinder D.
, p. 975 - 979 (2007/10/02)
15N N.m.r. spectroscopic results are reported for a range of covalent azides RNαNβNγ (where R is perfluoroaryl, perfluoro- or chlorofluoro-pyridyl or -pyrimidinyl, or trimethylsilyl), and compared with literature values for related azides.The Nα and Nγ chemical shifts vary over a range of 80-100 p.p.m, and correlate with weak long-wavelength bands in the electronic spectrum that arise from magnetically active transitions (n --> ?* and ? --> ?'*), the Nα,γ lines moving downfield as the bands move to lower energies.The Nβ chemical shift, however varies rather little from its value in the azide anion.The Nα,γ chemical shifts are sensitive to the known inductive and conjugative influences of the R group.Perfluorination increases the shielding, by increasing the energy of the paramagnetic circulation; the perfluoro-effect diminishing with distance from the fluoro-substituent, and with the extent to which n --> ?* circulations are important in the deshielding.Thus the patterns of chemical shifts are explained by the relationships of the frontier orbitals for rotation of charge in the magnetic field.
