Nitrogen NMR

Unprecedented Large Hyperpolarizability of Twisted Chromophores in Polar Media

“…28−30 This δ 15N trend also reasonably reflects increasing accumulation of positive charge at the benzimidazolium nitrogen atoms on progressing from B0TMC-2 to B2TMC-2 31−33 and indicates an increasing contribution of the aromatic resonance form to the groundstate structure. 34,35 Comparison of relative δ 15N values indicates a larger variation of the biaryl torsion between B0- and B1TMC-2 than between B1-and B2TMC-2 in agreement with NOE data (see below). Crystallographic Characterization of BXTMC-2 Chromophores.…”

“…In contrast to the above 1 H aromatic chemical shift trends, the 15 N chemical shifts (δ 15N ) of the benzimidazolium resonances (Figure , left) are displaced significantly and systematically within the BXTMC-2 series with δ 15N increasing from B0- (−216.8 ppm) to B1- (−214.0 ppm) and B2TMC-2 (−212.7 ppm). The observed δ 15N trend is determined by the paramagnetic contribution as is usual for nuclei heavier than 1 H. Consistently, a good linear correlation is obtained when plotting δ 15N versus the inverse of the optically determined HOMO–LUMO energy gap ( E CT , Table ) according to the Ramsey equation (Figure , right). − This δ 15N trend also reasonably reflects increasing accumulation of positive charge at the benzimidazolium nitrogen atoms on progressing from B0TMC-2 to B2TMC-2 − and indicates an increasing contribution of the aromatic resonance form to the ground-state structure. , Comparison of relative δ 15N values indicates a larger variation of the biaryl torsion between B0- and B1TMC-2 than between B1- and B2TMC-2 in agreement with NOE data (see below).…”

Insights into the Catalytic Activity of Nitridated Fibrous Silica (KCC‐1) Nanocatalysts from 15N and 29Si NMR Spectroscopy Enhanced by Dynamic Nuclear Polarization

“…The 15 N spectra of KCC‐1‐N600 and KCC‐1‐ 15 N700 are dominated by two resolved peaks near δ =10 and 25 ppm and can be assigned to NH 2 Si and NHSi 2 sites, respectively 19. 20 The deconvolution of the KCC‐1‐ 15 N700 spectrum indicates the presence of an additional site near δ =0 ppm, which can be assigned to ammonium ions 21. In none of the samples could we detect any signals for 15 NH 3 near δ =−32 ppm 22.…”

Insights into the Catalytic Activity of Nitridated Fibrous Silica (KCC‐1) Nanocatalysts from 15N and 29Si NMR Spectroscopy Enhanced by Dynamic Nuclear Polarization

“…[19,20] The deconvolution of the KCC-1-15 N700 spectrum indicates the presence of an additional site near d = 0 ppm, which can be assigned to ammonium ions. [21] In none of the samples could we detect any signals for 15 NH 3 near d = À32 ppm. [22] For T N values greater than or equal to 800 8C, the NHSi 2 peak becomes dominant.…”