Structure Determinations of Nitrogen Compounds with the Aid of NQR, NMR, and ESCA Spectroscopy

Abstract

Since it is often necessary or desirable to determine the structures of compounds containing nitrogen directly via the nitrogen atoms, the nuclear quadrupole resonance (NQR) and the nuclear magnetic resonance (NMR) as well as the photoelectron and the Augerelectron spectroscopy (ESCA) of nitrogen are becoming increasingly important. A comparative review of these three methods on the basis of measurement effect, information obtainable, applications, and limitations forms the subject of this article. IntroductionThree new fields of the spectroscopy ofnitrogen compounds, which have not yet been extensively used, are the 14N nuclear quadrupole resonance['', the * 4N and * 5N nuclear magnetic resonanceC2], and the photoelectron spectroscopy of nitrogenL3! Though these methods have been in practical use for a number of years, their wide application has been prevented mainly by experimental difficulties. In recent years there have been reports of some important technical improvements, which should lead to an increase in the capabilities of these methods and hence also to their wider use. On the other hand, an assessment of the methods with regard to their capabilities is possible on the basis of existing knowledge.The usual methods of nuclear magnetic resonance and IR and mass spectroscopy often do not yield conclusive answers in the determination of the structures of nitrogen compounds. Thus in mass spectroscopy, compounds that are difficult to volatilize sometimes suffer pyroiysis. Moreover, difficulties in interpretation often arise in the formation of zwitterions from salt-like nitrogen compounds or N-oxides. In IR analyses, it is difficult to distinguish between C=N and C = C bonds or between nitro and nitroso groups; it is also difficult to detect azo groupings and tertiary amines. The structures of molecules containing several nitrogen atoms, such as substituted polynuclear heterocycles, often cannot be determined by conventional NMR spectroscopy; the 'H resonance of compounds containing nitrogen is always negatively inff uenced by the nuclear quadrupole moment of the I4N nucleus. It is therefore often necessary or desirable to determine the structures of compounds containing nitrogen directly via the nitrogen atoms. Nuclear Quadruple ResonanceSince its introduction by Dehmelt and Kruger14.51 in 1950, nuclear quadrupole resonance spectroscopy has been in- Leverkusen-Bayerwerk (Germany) creasingly used for the investigation of chemical bonds in crystalline solids. Primarily through the work of Tomes and DaileyC61, it was possible to use the spectroscopic data to establish the electron structure of the chemical bond. The method is applicable to compounds of 130 isotopes whose nuclear spin is greater than 1/2. Nuclear quadrupole resonance thus complements nuclear magnetic resonance, since it can be used for the detection of the very nuclei whose measurement with the aid of nuclear magnetic resonance is impossible because of excessive line broadening due to quadrupole coupling.Apart from the investigations on hal...

Nuclear magnetic resonance spectrometry

“…lenes (95), polymers (96)(97)(98)(99)(100)(101)(102)(103)(104), NMR determination of optical and enantiomeric purity (105), applications of NMR in organic chemistry (106), NMR spectra of acridines (107), N-containing compounds (108), and heterocycles (109), double resonance (110)(111)(112)(113), the nuclear Overhauser effect (114), dynamic nuclear polarization (115)(116)(117), NMR and ultraslow motions (118), NMR at high magnetic fields (119,120), continuous-wave NMR techniques (121), relaxation (122), solvation of ions and ion pairs (123), solvent dependence of nuclear spin-spin coupling constants (124), NMR of gases (125), medium effects (126), high pressure NMR relaxation studies of liquids (727), bandshape phenomena for fluids (128), NMR at zero frequency (129), NMR of molecules oriented in electric fields (130) and oriented on solids (131) have all been reviewed. The NMR spectra of solids (132), superconductors and dilute alloys (133), water and ice (134), ferromagnets and antiferromagnets (135), NMR and conformational motion in solids (136), nuclear spin diffusion (137), application of NMR in stereochemical determinations (138) and isomerism problems (139), NMR of nitrogen (140), silicon…”