Chemical shift of thiazole

CARBON-13 CHEMICAL SHIFTS OF THIAZOLE AND SOME OF ITS DERTVATTVES (257,258)... 

TABLE L3L PROTON CHEMICAL SHIFTS OF THIA20LE AND VARIOUS MONOSUBSrrrUTED THIAZOLES ... 

TABLE 1-33 CHEMICAL SHIFTS OF PROTONS OF THE SUBSTITUENTS IN SUBSTITUTED THIAZOLE (235)... 

The chemical shifts of in natural abundance have been measured for thiazole and many derivatives (257,258). They are given in Tables 1-37 and T38. These chemical shifts are strongly dependent on the nature of the substituent CNDO/2 calculations have shown (184) that they correlate well with the ((t+tt) net charge of the atom considered. As a consequence, the order of the resonance signals is the same for protons and for carbon atoms. 

TABLE 1-38, CARBON CHEMICAL SHIFTS OF SUBSTITUE-NTS IN THIAZOLE AND SOME OF ITS DERIVATn/ES" (257)... 

The molar diamagnetic susceptibility of thiazole and some derivatives was initially determined by the classical Curie-Cheneveau method (5,315,316) and later confirmed by a method (317) based on the difference of NMR proton chemical shift of a sample of tetramethylsilane immersed in the liquid to be investigated, according to the shape (cylindrical or spherical) of the sample tube (Table 1-47) (318),... 

No nitration of thiazole occurs with the classical nitration reagents, even in forcing conditions (341-343). In a study concerning the correlation between the ability of thiazole derivatives to be nitrated and the HNMR chemical shifts of their hydrogen atoms, Dou (239) suggested that only those thiazoles that present chemical shifts lower than 476 Hz can be nitrated. From the lowest field signal of thiazole appearing at 497 Hz one can infer that its nitration is quite unlikely. Thiazole sulfonation occurs... 

Magnetic criteria have received wide application mainly as a qualitative test for aromaticity and antiaromaticity. The values of the exaltation of diamagnetic susceptibility (in 10-6A cm-3 mol-1), and therefore aromaticity, decrease in the sequence thiazole (17.0) > pyrazole (15.5) > sydnone (14.1). The relative aromaticity of heterocycles with a similar type of heteroatom can be judged from values of the chemical shifts of ring protons. The latter reveals paramagnetic shifts when Tr-electron delocalization is weakened. For example, in the series of isomeric naphthoimidazoles aromaticity decreases in the sequence naphthof 1,2-djimidazole (8 = 7.7-8.7 ppm) > naphtho[2,3- perimidine (8 = 6.1-7.2 ppm). This sequence agrees with other estimates, in particular with energetic criteria. 

The 13C-H spin coupling constants of thiazole have been determined on samples with 13C natural abundance or on samples specifically enriched in the 2-, 4- or 5-positions (Table 8). The 13C chemical shifts of benzothiazole are reported in Table 9. 

NMR study of nitrothiazoles has been the subject of few number of works [525, 530-540], The proton chemical shifts of about 30 thiazole derivatives including 5-nitrothiazole and 2-nitrothiazole are presented in [536], The authors have found the coupling constants between H-2 and II-4 in most 5-substituted thiazoles to be negligible with the exception of 5-nitrothiazole and 5-thiazolecarboxylic acids [536], The change in the H-4 chemical shifts of the 2-substituted 5-nitrothiazole fragment enables the ratio of isomeric products of the reaction of 5-nitrothiazole 2-(T,3 -dicarbonyl) derivatives with hydrazine and hydroxylamine to be established (Scheme 3.8) [537],... 

The H NMR chemical shifts of 5- and 6-substituted benzoxazoles, benzo-thiazoles, and benzoselenazoles were measured [737],... 

TT-Electron densities, correlation with proton chemical shift, of alkylthiazoles, 344 of phenylthiazoles, 345 Electronic charges, of thiazole, 31 of aminothiazoles, 44 of chlorothiazoles, 44 of methylthiazoles, 40 Electronic effects, of 5-substituents on quaternization, 390 Electronic paramagnetic resonance, 84 coupling constants for nitrothiazoles, 84 coupling constants for 2-thiazolyl radical, 84... 

J j 5N-H coupling constants in thiazole, 81 JNH coupling constants of thiazole, 80 line width of thiazole lines, 80 of monosubstituted thiazoles, 68 proton chemical shifts, of alkylthiazoles, 342... 

Thiazole shows a N chemical shift of 57.00 ppm relative to nitromethane when the spectrum is registered in pure liquid. The shielding of nitrogen remains practically unchanged in the fused ring of benzothiazole ((5 N of benzothiazole 61.00 ppm, acetone). Nitrogen-15 spectroscopy has been used in the characterization of neutral methanate complexes (ML2) between Zn and 2-thiazoline or benzothiazole derivatives <91G365>. 

The pXa value of oxazole itself has been determined240 by the chemical shifts of H-2 in acidic media and is 0.8 0.2 at 33°C. The feebly basic strength of oxazole relative to thiazole (pKa 2.53),297 pyridine (5.23),297 or 1-methylimidazole (7.33 )W8 is attributed primarily to the powerful inductive effect of the electronegative oxygen atom. This effect, evident in isoxazole (pX —2.03),240 299 is clearly more important than any base-strengthening effect from delocalization of the oxygen lone pair in oxazole. 

The H chemical shifts of some substituted pyrrolo[2,l-Z)]thiazoles are summarized in Table 5 <73JCS(P1)657, 86JCS(P1)I255>. 

In 2-substituted 2,3-dihydro-3-oxopyrrolo[2,l-fi]thiazoles, chemical shifts of aromatic protons are similar to those of 1,2-disubstituted pyrroles (83JHC591). 

The natural abundance C chemical shifts for thiazole (and its 2-, 4-, 2,4-, and 4,5-methyl derivatives) have been measured at 25.15 MHz against 50% enriched 82. The results confirm the accuracy of the C-H coupling constants, and show that the methyl groups exert an appreciable substituent effect on the carbon atoms to which they are attached. 2-Thiazoline (and its 2-methyl, 5-methyl, and 5-methyl-2-ethyl homologues) have also been studied from this point of view. ... 

The NMR spectra of thiazoles show the same behavior as those of aromatic compounds, but the chemical shifts also depend on the two heteroatoms. 

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