NMR carbonyls

Benzoates. The selective debenzoylation of sucrose octabenzoate [2425-84-5] using isopropylamine in the absence of solvents caused deacylation in the furanose ring to give 2,3,4,6,1/3/6 -hepta- and 2,3,4,6,1/6 -hexa-O-benzoyl-sucroses in 24.1 and 25.4% after 21 and 80 hours, respectively (54). The unambiguous assignment of partially benzoylated sucrose derivatives was accompHshed by specific isotopic labeling techniques (54). Identification of any benzoylated sucrose derivative can thus be achieved by comparison of its C-nmr carbonyl carbon resonances with those of the assigned octabenzoate derivative after benzoylation with 10 atom % benzoyl—carbonyl chloride in pyridine. 

Temperature-dependent 13C-NMR carbonyl signals of the [Cr(CO)4-(f/4-diene)] complexes 3a-3f, indicate an easy mutual conversion of the four [Cr(CO),(13CO)(iy4-dicne)] isotopomers a, d, e, and f (10,23). For this interconversion the barriers of activation were found to be between 39 and 47 lcJ/mol for complexes with acyclic diene ligands (Table II). Only in the case of tetracarbonyl-f/4-l,3-cyclohexadienechromium(0) (3g) is the carbonyl scrambling fast, even at 190 K. 

To take advantage of l9F NMR, carbonyl groups including quinones have been derivatized by reaction with trifluoromethyltrimethyl-silane in the presence of tetramethylammonium fluoride followed by hydrolysis of the trimethylsilyl ethers (Ahvasi et al. 1999). The method was applied to analysis of the various carbonyl groups in lignin. 

Figure 6. Expanded HNMR (A) and C NMR carbonyl region (B) of poly(BTMC-co-DON) with different molar composition PBTMC (Entry 1, Table 3) 86 14 BTMC.DON (Entry 2, Table 3) 54 46BTMC DON(Entry4, Table 3) 29 71 BTMC DON (Entry6, Table 3).

Figure 5 Variation of the urea/uron ratio of the C NMR carbonyl peak areas as a function of pH during the total reaction.

The effects of TIP also appear in figure B 1,11.3 and figure B 1.11.4. In the NMR spectrum, all the resonances of the sp carbons lie above 100 ppm (a usefiil general rule of thumb) because A is smaller for multiple bonds. The highest shifts are for the carbonyl C at 169 ppm and the ring C attached to oxygen at 155... 

The 4-Hydroxy-thiazoles are characterized by infrared absorption near 1610 cm (KBr) (3) or 1620 to 16.S0cm (CCI4) (8), indicating a strongly polarized carbonyl group. H-5 resonates near 5.6 ppm in the NMR spectrum like similar protons in other mesoionic compounds (3). Two fragmentations of the molecular ion are observed in the mass spectra. The first involves rupture of the 1,2 and 3,4 bonds with loss of C2R 0S . In the second, the 1,5 and 3,4 bonds are cleaved with elimination of C2R 0. ... 

The 4-hydroxy-THISs are extremely hygroscopic hydrolysis affords the parent thiobenzimide (3). When R" = Me and R = p-ClPh or Ph, but not p-NOjPh the nondipolar tautomer 3 (X = 0, Y = CH2) is present according to NMR and infrared spectra, the latter exhibiting carbonyl absorption at 1710 to 1720 cm ... 

The reasonable stable products are characterized by an ir-absorption near 1615 cm". The 4-protons resonate near 6.2 ppm in the H NMR spectrum (23). NMR spectra exhibit a carbonyl atom signal near 173 ppm, whereas C-4 resonates near 8 108 these positions are characteristic of other mesoionic ring carbon atoms (24). In the mass spectra, decomposition with loss of CO, rupture of the 1,5 and 2.3 bonds with elimination of R NC2R 0 and cleavage of the 1,2 and 3,4 bonds with elimination of C2R 0S is observed (11)... 

A compound has the molecular formula C4HgO and contains a carbonyl group Identify the compound on the basis of its H NMR spectrum shown in Figure 17 20... 

NMR Like other carbonyl groups the carbon of the —CO2H group of a car boxylic acid is strongly deshielded (8 160-185) but not as much as that of an aldehyde or ketone (8 190-215)... 

C NMR The C NMR spectra of carboxylic acid derivatives like the spectra of carboxylic acids themselves are characterized by a low field resonance for the carbonyl... 

Section 20 21 Acyl chlorides anhydrides esters and amides all show a strong band for C=0 stretching m the infrared The range extends from about 1820 cm (acyl chlorides) to 1690 cm (amides) Their NMR spectra are characterized by a peak near 8 180 for the carbonyl carbon H NMR spectroscopy is useful for distinguishing between the groups R and R m esters (RCO2R ) The protons on the carbon bonded to O m R appear at lower field (less shielded) than those on the carbon bonded to C=0... 

The infrared carbonyl stretching frequencies of n- and isobutyraldehyde in the condensed phase occur at 1727.6 and 1738.0 cm , respectively (38). The proton nmr spectra of both aldehydes are weU-known (39). 

A comparison of the relative basicities of pyrrole, furan and thiophene may be made by comparing the pK values of their 2,5-di-t-butyl derivatives, which were found to be -1.01, —10.01 and —10.16, respectively. In each case protonation was shown by NMR to occur at position 2. The base-strengthening effect of alkyl substitution is clearly apparent by comparison of pyrrole and its alkyl derivatives, e.g. A-methylpyrrole has a pKa. for a-protonation of -2.9 and 2,3,4,5-tetramethylpyrrole has a pK of 4-3.7. In general, protonation of a-alkylpyrroles occurs at the a -position whereas /3-alkylpyrroles are protonated at the adjacent a-position. As expected, electron-withdrawing groups are base-weakening thus A-phenylpyrrole is reported to have a p/sTa of -5.8. The IR spectrum of the hydrochloride of 2-formylpyrrole indicates that protonation occurs mainly at the carbonyl oxygen atom and only to a limited extent at C-5. 

---