NMR spectroscopy in environmental chemistry:1H and13C NMR chemical shift assignments of chlorinated dibenzothiophenes based on two-dimensional NMR techniques andab initio MO and DFT/GIAO calculations

1H and 13C NMR assignments of dihydropipataline, the main of four long‐chain 1‐(3,4‐methylenedioxyphenyl)‐alkanes from Piper darienence D.C.

“…To perform the complete 13 C NMR chemical shifts assignment of 3, including the signals for aliphatic carbons C-3 to C-7, spectral 13 C NMR simulations and ab initio DFT-GIAO methods were applied. Recent applications of ab initio DFT-based methods have provided results accurate enough for the solution of NMR signal assignments [16][17][18][19][20]. In particular DFT-GIAO NMR calculations on molecules with saturated long-chains have not been reported.…”

“…In particular DFT-GIAO NMR calculations on molecules with saturated long-chains have not been reported. In the case of 3, with a twelve-carbon atom side-chain, the calculation was carried out on the ab initio DFT optimized geometry using the widely utilized density funtionals BPW91 [17][18][19][20][21][22] and B3LYP [21,23] Table 2. At first attempt theoretical calculated shifts (δC calc , ppm) were obtained by substraction of the calculated σ IMS from that for the standard TMS δC calc = σ IMS(3) − σ IMS(TMS) , however the rms error obtained for aliphatic side-chain carbons C-1, C-2 and C-8 to C-12 (∼7 ppm) hardly seems adequate for a reliable assignment of the spectrum.…”