The International Union of Pure and Applied Chemistry (IUPAC) recommends using CHNO as the experimental standard; however in practice many spectroscopists utilize pressurized NH(l) instead. For N, chemical shifts referenced with NH(l) are 380.5 ppm upfield from CHNO (δNON are somewhat erratic but typically they span a range of -400 ppm to 1100 ppm with respect to CHNO. Below is a summary of N chemical shifts for common organic groups referenced with respect to NH, whose chemical shift is assigned 0 ppm.