15N, 13C and 1H nuclear magnetic shielding and spin–spin coupling constants of 1- 13C, 15N-enriched acetonitrile in gaseous mixtures with SF 6 and CO 2

Abstract

The 15N, 13C, and 1H absolute magnetic shielding of a CH 3 13C 15N molecule has been determined from NMR measurements in the gas phase at 300 K: σ 0( C N )=−8.873(5) ppm, σ 0( C N)=74.021(3) ppm and σ 0( C H 3)=29.113(1) ppm. It is shown that intermolecular shielding effects for the 13C and 15N nuclei in the cyano group are large and in the opposite directions. For the first time the dependence on density has also been observed for the 1 J(NC), 2 J(CH) and 3 J(NH) spin–spin coupling when the HSQC spectra of CH 3 13C 15N have been analyzed. It has permitted us to obtain the coupling constants free from intermolecular interactions: 1 J 0(NC)=−16.20(1) Hz, 2 J 0(CH)=−10.18(2) Hz and 3 J 0(NH)=−1.34(2) Hz. The new experimental results may be useful for the verification of appropriate ab initio calculations for an acetonitrile molecule.