Shift ring proton

Nuclear magnetic resonance spectra of 2-aminothiazole and of 2-imino-4-thiazoline were reported during the studies related to protomeric equilibria (125-127) ring protons in the former are centered at 6.48 and 7.14 ppm (internal Me4Si), while those in the latter are shifted upheld to 5.8 and 6.5 ppm (125). 

A 2-methylthio substituent decreases the basicity of thiazole pK = 2.52) by 0.6 pK unit (269). The usual bathochromic shift associated with this substituent in other heterocycles is also found for the thiazole ring (41 nm) (56). The ring protons of thiazole are shielded by this substituent the NMR spectrum of 2-methylthiothiazole is (internal TMS, solvent acetone) 3.32 (S-Me) 7.3 (C -H) 6.95 (Cj-H) (56, 270). Typical NMR spectra of 2-thioalkylthiazoles are given in Ref. 266. 

By trapping PX at liquid nitrogen temperature and transferring it to THF at —80° C, the nmr spectmm could be observed (9). It consists of two sharp peaks of equal area at chemical shifts of 5.10 and 6.49 ppm downfield from tetramethylsilane (TMS). The fact that any sharp peaks are observed at all attests to the absence of any significant concentration of unpaired electron spins, such as those that would be contributed by the biradical (11). Furthermore, the chemical shift of the ring protons, 6.49 ppm, is well upheld from the typical aromatic range and more characteristic of an oletinic proton. Thus the olefin stmcture (1) for PX is also supported by nmr. 

Table 2 H Chemical Shifts of Protons on the Heterocyclic Rings of Simple Benzazines cf. naphthalene, column 1)...

Chemical shifts in parentheses are for the methyl group of the substituent. Coupling constants in parentheses are between the substituent methyl group and the indicated ring proton. 

Annelation of a benzene ring on to the [Z>] faee of the heteroeyelie ring does not have any pronouneed effeet upon the ehemieal shifts of the heteroeyelie protons (cf. Table 8). The rather unexpeeted heteroatom sequenee for shifts to progressively lower field for both H-2 and H-3 remains NHsolvent dependent and as in pyrrole it is also eoupled to the ring protons with Ji,2 = 2.4Hz and Ji,3 = 2.1 Hz. The assignment of the benzenoid protons H-5 and H-6 has eaused some eonfusion in the literature as they have almost... 

Aromatic character in isoxazoles has been studied from a number of viewpoints, and these studies indicate that although isoxazole may be formally considered an aromatic system, the disposition of the ring heteroatoms modifies this character to an appreciable extent. From a qualitative viewpoint, thermal stability and electrophilic attack at the 4-position may be considered consistent with an aromatic character. Furthermore, NMR chemical shifts of the ring protons are consistent with those of an aromatic compound. References related to these studies may be found in Section 4.16.2.3.4. 

In Fig. 2.7 the H signal with a typieal aromatie proton shift of Sh =7.1 shows a doublet of doublets with 7-values of 8.5 Hz ortho eoupling, Jhh) and 2.5 Hz meta eoupling, V////). The ring proton in question therefore has two protons as eoupling partners, one in the ortho position 8.5... 

The present authors have found that the preparation of 7V-acetyl aziridine derivates provides the most secure method of differentiating aziridines from primary amines which are alternate reaction products in a number of cases. The infrared spectra of the former derivatives show only a peak at 1690 cm" for a tertiary amide peaks at ca. 3440 and 1530 cm" indicative of a secondary amide are absent. Acetylation also shifts the aziridine ring protons to a lower field in the NMR by ca. 1 ppm relative to the parent aziridine. The A"-acetyl aziridines are hydrolyzed with 3% methanolic potassium hydroxide. " Published NMR spectra of several 16j5,17j -aziridines reveal resonance patterns resembling those of the respective epoxides. " ... 

Ring current (Section 15.8) The circulation of tt electrons induced in aromatic rings by an external magnetic field. This effect accounts for the downfield shift of aromatic ring protons in the lH NMR spectrum. 

Benzyl alcohol. We have demonstrated that all benzyl aleohol (BzOH) moleeules dissolved in water are also immediately transported and trapped in the lipid bilayer phase, when it is mixed with EPC bilayer [46]. The trapped site of BzOH, however, differs from that of PrBe. As shown in Fig. 8, the ring proton signal of BzOH in water is at first broadened and shifted to a higher field [from (a) to (b)j then the signal is split into two (e). 

In order to evaluate the DD site semiquantitatively, we have analyzed the chemical shift change A.S of the ring proton signals of PrBe and BzOH on the delivery from water to... 

TABLE 6 Chemical Shift Difference of the Ring Proton Signals of PrBe and BzOH Delivered to the EPC SUV from the Water Phase... 

The DD site can be ensured by the chemical shift changes of the BPA signals. The chemical shift differences of the ring proton signals of BPA on the delivery from water to bilayer phases are —0.04 and —0.11 ppm for the ortho and meta sites, respectively. Negative values mean upfield shifts recall the HCS rule. It is concluded that both benzene rings of BPA are trapped in the bilayer from the water phase and the meta site penetrates more deeply into the hydrophobic interior. 

The UV spectrum closely resembles that of tropone and exhibits a batho-chromic shift over those of cycloheptatriene (unconjugated). Although the "B signal at 53.6 ppm is not much shifted over that in 1-phenyl-4,5-dihydroborepin (54.6 ppm), the borepin ring protons occur at markedly... 

The NMR chemical shifts of the polymers 10 and 11 are only slightly dependent on the molecular weight. The NMR spectrum of the polymer 10 shows three shrap resonances at 6 0.34, 0.94, and 7.28 ppm, due to MeSi, EtSi, and phenylene ring protons, while the polymer 11 reveals shrap resonances at 6 0.62, 7.28, and 7.35 ppm, attributed to MeSi and phenyl ring protons. The polymers 10 and 11 show characteristic strong absorption bands at 262 and 254 nm, respectively, significantly red-shifted relative to pentamethylphenyl-disilane which exhibits an absorption band at 231 nm. 

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