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A new experimental absolute nuclear magnetic shielding scale for oxygen based on the rotational hyperfine structure of H 2 O 17 A revised experimental absolute magnetic shielding scale for oxygen General scales of community reaction to noise (dissatisfaction and perceived affectedness) are more reliable than scales of annoyance For the first time, oxygen-17 chemical shifts together with experimental details are reported for CO, CO 2 , OCS, N 2 0, and OF 2 • An absolute 170 shielding scale, based on a recent redetermination of the 170 spinrotation constant in C 170 is proposed: u (C 170) = -42.3 ± 17.2 ppm. Absolute shielding constants derived from 170 NMR chemical shifts are compared with those calculated from recent molecular orbital studies. Also scalar coupling constants involving 170 are reported for OF 2 and CO. In OF 2 , J (F,O) = 300 ± 30 Hz; in carbon monoxide, J (O,C) is less than 5 Hz.

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Articles you may be interested inCommunication: Localized molecular orbital analysis of the effect of electron correlation on the anomalous isotope effect in the NMR spin-spin coupling constant in methane Oxygen isotope shifts on the 13C chemical shifts and carbon isotope shifts on the 17 0 chemical shifts in carbon monoxide and carbon dioxide are reported. Using models developed by Jameson, shielding derivatives with respect to bond lengths can be calculated using the measured isotope shifts. For carbon monoxide, the derivatives were calculated to be [au (13C)/arJe = -456 ± 15 ppm/A. and [au ( 17 0)/arJe = -1150 ± 130 ppm/A.. Although earlier coupled Hartree-Fock calculations give a much lower value for [au ( 17 0)/arJe' recent ab initio calculations for carbon monoxide agree very well with our experimental results. Furthermore, the observed 18 0/ 16 0 isotope shift is similar to values measured previously for a series of metal carbonyls. For carbon dioxide the iostope shift gives [au (13C)/arJe = -214 ± 17 ppm/ A. which is in excellent agreement with the value obtained from a recent variable temperature gas phase NMR study. In addition, scalar spin-spin coupling constants, IJ(13C, 17 0) were measured to be 16.4 ± 0.1 Hz in carbon monoxide and 16.1 ± 0.1 Hz in carbon dioxide. To our knowledge, these are the first directly measured carbon-oxygen coupling constants to be reported in the literature. From general trends in the periodic table, it seems likely that the sign of these coupling constants is positive.

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