Benzenes nuclear magnetic resonance

Nuclear Magnetic Resonance Spectroscopy. Nmr is a most valuable technique for stmeture determination in thiophene chemistry, especially because spectral interpretation is much easier in the thiophene series compared to benzene derivatives. Chemical shifts in proton nmr are well documented for thiophene (CDCl ), 6 = 7.12, 7.34, 7.34, and 7.12 ppm. Coupling constants occur in well-defined ranges J2-3 = 4.9-5.8 ... 

Analysis. The infrared (ii), ultraviolet M, and nuclear magnetic resonance (nmr) spectra are distinct and characteristic for benzene and are widely used in analysis (78—80). Benzene also produces diagnostic ions in the mass spectmm (81,82) (see Analytical methods). 

Nuclear magnetic resonance measurements have led to the conclu-sion that 2-pyridones have about 35% of the aromaticity of benzene and that the formally related l,2-dihydro-2-methylenepy-ridine is not aromatic. A substantial contribution by such resonance is indicated by the electronic spectrum of 2-quinolone, which is... 

The ratio [Sc(Cp )2Ph] / [Sc(Cp )2H] was obtained from relative heights of H nuclear magnetic resonance (NMR) peaks, and [C6H6] was calculated from the density of benzene. The determination of [H2] was more complicated because this substance is also involved in a gas-liquid equilibrium. The procedure used by the authors is as follows. 

Spectroscopy data Infrared (proton [5830] grating [33038]), nuclear magnetic resonance (proton [6575] C-13 [2936]) and mass spectral data have been reported (Sadtler Research Laboratories, 1980 Lide Milne, 1996) Solubility Very soluble in water (954 g/L) and ethanol slightly soluble in benzene and diethyl ether (Lide Milne, 1996 Verschueren, 1996)... 

The chemical properties of these complexes, together with their infrared and high resolution nuclear magnetic resonance spectra, show that the cyclopentadiene group is bound to the iron atom as shown in (XXII). By sharing the six Tr-elccIrons of the benzene molecule and the four -electrons of the cyclopentadiene molecule, the iron(O) atom acquires the electronic configuration of krypton. 

Normalization, 6 Normal modes, 240-244 of benzene, 438-439 of boron trifluoride, 281, 290 of carbon dioxide, 242, 248, 262, 265 of ethylene, 291 and group frequencies, 266-268 IR active, 457 Raman active, 457 and symmetry, 246-249,430-439 of water, 431-437 Normal operator, 108 Nuclear g factor, 3 24 Nuclear magnetic moments, 323-325 Nuclear magnetic resonance, 129-130, 323-366... 

All NMR spectra were recorded on a Varian A-60 spectrometer at room temperature by Nuclear Magnetic Resonance Specialties, Inc., New Kensington, Pa. Benzene soluble fractions were recorded in deuterated chloroform solution (CDCls) while dimethyl sulfoxide-dc (DMSO-dr.) was the solvent employed for other fractions. (Deuterated chloroform with enrichment of 99.8% was purchased from Bio-Rad Laboratories and dimethyl sulfoxide-dr, with enrichment of 99.6% from Merck, Sharp, and Dohme of Canada.) The internal standard used with the CDCla solutions was tetramethvlsilane and hexamethyl-disiloxane (chemical shift 7 c.p.s.) with DMSO-d . Prior to preparation for NMR recording, the samples were thoroughly dried in a vacuum at 110°C. The NMR tubes were sealed to minimize the absorption of atmospheric moisture. The chemical shifts given in c.p.s. are referred to tetramethylsilane. 

Proof for the existence of benzene isomers in irradiated benzene has been obtained in several ways. These will not be discussed in detail, but they may be classified broadly as physical and chemical. Nuclear magnetic resonance has been used by Wilzbach and Kaplan to identify benzvalene.39 Prismane has also been identified by NMR and by vapor-phase chromatography. The Dewar form has been synthesized in several steps which start with ris-1,2-dihydrophthalic anhydride. Photochemically this compound yields bicyclo(2,2,0)hexa-5-ene-2,3-dicarboxylic aqid anhydride. This was followed by catalytic reduction and oxidative decarboxylation to give the Dewar form of benzene.39 The method of synthesis alone provides some basis for structure assignment but several other bits of supporting evidence were also adduced. Dewar benzene has a half-life of about 48 hr at room temperature in pyridine solution and its stability decreases rapidly as the temperature is raised. 

The behavior of substituted benzenes does not afford adequate proof that benzene would behave in a similar way. There are two lines of evidence that it does (/) 1,3,5-trideuterobenzene isomerizes to benzenes with different deuterium distributions43 (the status of this work is at present not entirely satisfactory) and (2) benzvalene has been identified by nuclear magnetic resonance in liquid benzene exposed to ultraviolet light.41... 

The ground-state complex between benzene and maleic anhydride was found to have the exo configuration. Bryce-Smith and Hems [44] have measured nuclear magnetic resonance chemical shifts of the ethylenic protons of maleic an-... 

Although several metal-containing heterocyclic compounds (such as porphyrins, phthalocyanines, naphthenates) are present in oil fractions most of the bench-scale research has been based on relatively rapid Ni, V, or Ni/V deposition procedures in which experimental FCC formulations have been artificially metal contaminated with solutions of Ni and/or V naphthenate dissolved in benzene (or toluene) (24). Metal levels in these novel FCC are usually above 0.5% that is well above the concentration that today exist on equilibrium FCC, see Figure 1. High metal concentration facilitate the study and characterization of Ni and V effects by modern characterization techniques such as X-ray photoelectron spectroscopy (XPS), Laser Raman spectroscopy (LRS), X-ray diffraction (XRD), electron microscopy, secondary ion mass spectrometry (SIMS), and 51V nuclear magnetic resonance (NMR). 

A recent paper describes the reaction of 2-pyridone with sulfur dichloride when these are boiled in benzene for a week the 5,5 -dipyridyl sulfide (80) is formed in 13% yield. The structure of 80 was confirmed by its ultraviolet and nuclear magnetic resonance (NMR) spectra.173 3-Hydroxypyridine gives a poorly defined and apparently high polymeric substance under these conditions, whereas 4-pyridone is said not to react. 

Nuclear Magnetic Resonance Spectroscopy. Nmr is a most valuable technique for structure determination in thiophene chemistry, especially because spectral interpretation is much easier in the thiophene series compared to benzene derivatives. Chemical shifts in proton nmr are well documented for thiophene (CDC13), 6 = H2 7.12, H3 7.34, H4 7.34, and H5 7.12 ppm. Coupling constants occur in well-defined ranges J2 3 = 4.9-5.8 J3 4 = 3.45-4.35 J2 4 = 1.25-1.7 and J2 5 = 3.2-3.65 Hz. The technique can be used quantitatively by comparison with standard spectra of materials of known purity. 13C-nmr spectroscopy of thiophene and thiophene derivatives is also a valuable technique that shows well-defined patterns of spectra. 13C chemical shifts for thiophene, from tetramethylsilane (TMS), are C2 127.6, C3 125.9, C4 125.9, and C5 127.6 ppm. 

---