HNMR Spectroscopy

Treatment of ethyl 2,7-di-/ert-butylthiepin-4-carboxylate (24) with 3-chloroperoxybenzoic acid at — 78 °C results in the benzene derivative 25 only, and no sulfur-oxidized products 80 however, the stable 2,7-di-ter/-butylthiepin (26) can be oxidized with 0-benzyl 00-hydrogen monoper-oxycarbonate at — 78 °C to give the corresponding S-oxide 27, which was monitored by HNMR spectroscopy at — 40°C. At —15 C, sulfoxide 27 was converted, via extrusion of sulfur monoxide, with a half-life of 5.5 hours to the benzene derivative 28.87 The oxidation reaction of 26 with excess of the monoperoxycarbonate did not proceed to the S,S-dioxide, even though the parent thiepin 1,1-dioxide is known to be stable at room temperature.15... 

The synthesis of monocyclic thiepins from thiophene and dimethyl acetylenedicarboxylate is often accompanied by the loss of sulfur. In particular, in cases where room temperature is required for efficient rates of cycloaddition and rearrangement76 (see Section 2.1.3.3.), the desulfurization reaction proceeds rather quickly with the consequence that thiepin formation can be monitored by low temperature HNMR spectroscopy, but the products cannot be isolated.76 - 78 However, in the case of thiepin 1 where R1 = R2 = C02Me and R3 = H, refluxing toluene is necessary for the extrusion of sulfur.78... 

Ring inversions of 1H- and 4//-azepines between their two stable boat forms have been studied extensively by HNMR spectroscopy.37,38-40-76 82,85 A coalescence temperature of — 55 7 C and a AG value for ring inversion of 42.7 kJ mol have been determined for the two conformers 10 A and 10 B of A-phenyl-3//-azepin-2-amine.82... 

Determined by HNMR spectroscopy of the crude reaction mixture. 

In the case of 6-isopropyl-2-methylphenyl azide a 1 1 mixture (by HNMR spectroscopy) of 3-isopropyl-A%V,7-trimethyl-3//-azepin-2-amine and 7-isopropyl-N,N,3-trimethyl-3//-azepin-2-amine is obtained in 45% yield. 

Cyanophenyl azide is of interest in that on photolysis in methanol/tetrahydrofuran solution, an unseparated 1 1 mixture (by HNMR spectroscopy) of 2-methoxy-3//-azepine-3-carbonitrile and -7-carbonitrile (44%) is formed.197-282 Likewise, irradiation of 2-azidophenyl methyl ketone in methanol furnishes a mixture of 3-acetyl-2-methoxy- (11 %) and 7-acetyl-2-methoxy-3//-azcpine (3%) along with 3-methyl-2,l-benzisoxazole (18%).78... 

As expected, similar treatment of 3-nitroarenes furnishes mixtures of 4- and 6-substituted 3H-azepines, 54 and 55, respectively.176 Comparable yields of mixed azepines were also obtained by deoxygenation of 3-nitroarenes with alkylphophorous triamides, formed in situ from hexa-methylphosphorous triamide and excess of a secondary amine.66 In a few cases the 3//-azepines were separated by fractional crystallization of their oxalate salts66 but, in general, pure isomers were not isolated and the yields cited in the table were determined by HNMR spectroscopy. 

Irradiation of 3-benzoyl-2-methoxy-3//-azepine (32) in methanol gives rise to a mixture of the 3-azabicyclo[4.1.0]hepta-2,4-diene 33 (detected by HNMR spectroscopy, but not isolated), 2-methoxy-3-phenacylpyridine(34), and a trace of 2-phenylfuro[2,3-A]pyridine (35), this last product being an artefact derived from the phenacylpyridine 34.246... 

An X-ray structural analysis has confirmed that ethyl 1//-azepine-1-carboxylate (1) and nitrosobenzene yield the [6 + 2] adduct 1 1 183-254 255 Subsequently, however, a careful analysis of the reaction mixture by HNMR spectroscopy indicated that a [4 1 2] adduct is also formed, albeit in low yield, to which structure 12 was assigned.256... 

Characterization of the modified plastocyanins was by Inductively Coupled Plasma Emission Spectroscopy to analyze for Ru and Cu (1 1 ratio), and by HNMR spectroscopy. In the HNMR characterization the C2H resonance of His59 at 8.2 ppm is seen to be lost due to paramagnetic line broadening effect of the attached Ru(III), Fig. 13 [50]. In a further test it is known that the His59 s of both native plastocyanins react with diethyl pyrocarbonate (DEPC) to give an JV-ethoxyhistidine derivative, (12), which absorbs strongly at 238 nm (e 2750M- cm-i), Fig. 14 [133]. 

Reactions were carried out mainly at 40° C with deuteroacetonitrile, CD3CN, as the usual solvent. Monomer and initiator consumptions were monitored simultaneously by HNMR spectroscopy. The structure of the active centres was also assessed by NMR and in addition the concentration of propagating species could be calculated at any time during the reaction. A simple mechanism involving initiation kh and propagation kp, was proposed, and both rate constants were readily determined. 

The important role that HNMR spectroscopy has played in the study of the ring conformations of pyrrolidines and related compounds will be discussed in Section 3.04.5.3. 

HNMR spectroscopy has been used to distinguish between the two isomeric products obtained as a mixture in the reaction of 5,8-dichloro-2-phenylpyrimido[4,5-rf]pyridazine with aliphatic amines. In these reactions the isomeric products are separated by column chromatography and then the chemical shift of the H-4 proton is noted. This proton is shifted to lower field (ca. 8 10.2) for the 5-amino substituted products (39), when compared with the chemical shift (ca. 8 9.9) for the 8-amino substituted products (38) (72CPB1522). Chemical shifts for several pyrimido[4,5-rf]pyridazin-5-ones have also been reported (Table 2) (76BSF1549). 

Homeman, A.M. etal. Highly Functionalised Cyclopentanes by Radical Cyclisation of Unsaturated Bromolactones III. Preparation of Carbaaldohexofuranoses. Determination of the Relative Configuration at C-4/C-5 of 2,3-Unsaturated Heptono-1,4-lactones by Means of HNMR Spectroscopy. 2.1 1999(126]... 

The benzomorphan structure with an oxygen function in either the 1- or 11-position offers a means of building an acetylcholine moiety onto a sterically constrained support, and such compounds could afford evidence for the steric requirements of acetylcholine at its nicotinic and muscarinic receptors. Pairs of a- and /3-isomers of 1- and 11-acetoxybenzomorphan quaternary salts 182 and 183 have been synthesized and their stereochemistry established by Hnmr spectroscopy.01S)... 

Tetrafluoroborates recrystallizcd from abs EtOH and fluorides from magnesium-dried ( superdry") EtOH. Relative ratios determined by HNMR spectroscopy (in CDCI3). 

The red fox (Vulpcs wipes) uses a chemical communication system ha. ted on scent marks in urine. Recent work has shown one component of fox urine to be a sultlde. Muss spectral ana lysis of the pure acent murk t iijnpoiwnc.sh[Pg.737]

To a solution of enamine in CH2C12 was added a solution of l-fluoropyridin-2(l/f)-one (9 ca. 1 to 4 molar equiv) in CH2C12, and the mixture was allowed to reflux. Alter the appropriate time, the mixture was stirred with aq HCI and the crude fluoro ketone was analyzed by 19F and HNMR spectroscopy, and GC. 

West and coworkers on the basis of HNMR spectroscopy suggest that (MeAs)5 is in rapid equilibrium with open-chain oligomers, which are in turn in slow equilibrium with higher polymeric species ... 

Microwave spectroscopy and dipole moment measurements HNMR spectroscopy NMR spectroscopy... 

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