The rotational spectrum of nitrosobenzene in the first four excited states of the torsional vibration has been observed. The vibrational fundamental is at about 100 cm−1. The barrier to rotation around the C–N bond is 3.9±1 kcal/mole, based on relative intensity measurements. Variations in the inertia defect in the excited states are compared with theory. The next-lowest vibrational state is at about 220 cm−1 and is an in-plane vibration.
The microwave spectrum of nitrosobenzene has been studied in the frequency region between 13 000 and 24 000 Mc/sec. Numerous a-type, R-branch transitions have been identified, and the rotational constants have been determined. The molecule is completely planar with the C–N=O group bent at an angle of about 116° in the plane of the ring.
There is a large contact term contribution to 13C paramagnetic shifts induced by Eu(dpm),, Pr(dpm),, and Eu(fod), in pyridine and p-picoline ; this contribution may not be due mainly to spin delocalization through n-bonds.ALTHOUGH it is generally accepted that paramagnetic shifts induced by some lanthanide complexes are mainly due to pseudo-contact interactioql it has been recently reported that abnormal shift values are observed for atoms (14N), co-ordinated to the lanthanide ion2 and for 13C or lH nuclei close to the co-ordinating atom in some aliphatic corn pound^.^ Johnson et al. have reported that abnormal relative lH shift patterns are observed for substituted pyridine N-oxides and anilines with some lanthanide complexes, and that the shift patterns for these substrates with Eu(fod), are characteristic of a contact interaction attributed to n-spin density.4 For pyridine derivatives, the observed shifts induced by La(dpm), (La = Pr, Eu, and Yb) could be interpreted approximately in terms of a pseudo-contact interaction only by using a distance between nitrogen and lanthanide ion of 4 k 5 Huber et al. tenta-31.
1H and 13C paramagnetic shifts induced by Eu(DPM)3 and Pr(DPM)3 in acridine, quinoline, and isoquinoline in CCl4 are observed. It has been found that, while the 1H shifts can be interpreted solely in terms of a pseudo-contact interaction, there is a much larger contact-term contribution to 13C shifts induced by Eu(DPM)3 than by Pr(DPM)3 in these compounds; this contribution to the 13C shifts cannot be explained by a simple combination of σ- and π-contact terms.
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