14N Chemical shifts are reported for hydrazoic acid, certain organic and organoarsenic azides, and a number of metal azido-complexes. The shifts are related where possible to the electronic characteristics of the atom or group to which the azide is covalently attached and to the mode of attachment.No spin-spin coupling effects are observed but the shifts provide some evidence for molecular association or azide exchange in the compounds Me2AsN, and Et,AsN,.The covalent character of the metal-azide bond is demonstrated by the appearance of three distinct 14N n.m.r. signals for each of the azido-complexes studied.

14N N.m.r. spectroscopy has been used to investigate the nature of species in non-aqueous solutions of some covalent diamagnetic metal nitrato-compounds. Certain covalent nitrates of non-metals have also been studied for purposes of comparison. Solutions of the metal nitrates in CCI, and MeNO, show chemical shifts which clearly indicate their covalent nature but fail to distinguish the bonding mode. Solutions in electron-pair donor solvents exhibit generally lower shifts, attributed to partial dissociation of nitrate ligands as a result of solvent-donor and dielectric influences. The suitability of pure nitric acid as a solvent and reaction medium for covalent metal nitratocompounds has also been examined by the 14N n.m.r. technique.THE ability of the nitrate group to behave as a unidentate, MONO,, bidentate, MO,NO, bridging bidentate, MON(O)OM, or bridging terdentate, MON(OM)OM, ligand in solid metal nitrates and nitrato-complexes has now been amply demonstrated by recent X-ray crystallographic investigations 1-5 and the broad structural principles (e.g. the influence of d-electron configuration on molecular geometry) operative in such systems are beginning to emerge. Vibrational spectroscopy of solid

The origin band of the Ã1B2-X1A1 (π* ← π) absorption system in monodeuterated tropolone (TrOD) has been probed with near-rotational resolution by applying the frequency-domain techniques of polarization-resolved degenerate four-wave mixing (DFWM) spectroscopy under ambient, bulk-gas conditions. Judicious selection of polarization geometries for the incident and detected electromagnetic waves alleviated intrinsic spectral congestion and facilitated dissection of overlapping transitions, thereby enabling refined rotational-tunneling parameters to be extracted for the Ã1B2(π*π) manifold. A tunneling-induced bifurcation of Δ0Ã = 2.241(14) cm(-1) was measured for the zero-point level of electronically excited TrOD, reflecting the presence of a substantial barrier along the O-D···O ↔ O···D-O reaction coordinate and representing nearly a 10-fold decrease in magnitude over the analogous quantity in the parent (TrOH) isotopologue. Observed trends in hydron-migration rates are discussed in light of the changes in the potential-surface topology sustained from the π* ← π electron promotion and the dynamical effects incurred by selective isotopic modification of the nuclear framework, with similar considerations being applied to interpret rotational constants and inertial defects. Simultaneous analyses performed on an interloping sequence band built upon ν38(b1) gave an excited-state tunneling splitting of Δ(ν38)Ã = 1.217(61) cm(-1), highlighting the ability of this symmetric, out-of-plane normal mode to inhibit the unimolecular tautomerization process.

A 14N n.ni.r. study of the NCO group in a range of nitrogen-bonded compounds and in certain oxygenbonded species demonstrates the value of 14N chemical shifts in distinguishing these bonding modes.

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