An improved carbon-13 nuclear shielding scale

Abstract

An improved scale for carbon-13 nuclear shielding is proposed based upon the primary reference point σ(300 K)= 0.6 ± 0.9 ppm for low-density gaseous carbon monoxide. This result is obtained by combining a diamagnetic part obtained from a very recent high quality ab initio calculation with a paramagnetic part deduced from an experimental spin-rotation interaction constant. Careful consideration of vibration-rotation effects is essential as they contribute ca. 2.2 ppm to the shielding.