ICS-NMR

H.O. Kalinowski, S. Berger u. S. Braun, 1 iC-NMR-Spektroskopie. S. 177, 193, Georg Thieme Verlag, Stuttgart New York 1984. 

Problem 13.6 Assign the resonances in the, iC NMR Bpectrum of methyl propanoate, CH3CH2C02CH3 (Figure 13.10). 

Carboxylic acid groups can be detected by both and 1 iC NMR spectroscopy. Carboxyl carbon atoms absorb in the range 165-185 6 in the 13C NMR spectrum, with aromatic and a,(3-unsaturated adds near the upheld end of the range (-165 8) and saturated aliphatic acids near the downfield end (-185 8). The acidic -COOH proton normally absorbs as a singlet near 12 8 in the H NMR spectrum. As with alcohols (Section 17.12), the -COOH proton can be replaced by deuterium when D20 is added to the sample tube, causing the absorption to disappear from the NMR spectrum. 

The principal techniques for determining the microstmcture of phenoHc resins include mass spectroscopy, proton, and C-nmr spectroscopy, as well as gc, Ic, and gpc. The softening and curing processes of phenoHc resins are effectively studied by using thermal and mechanical techniques, such as tga, dsc, and dynamic mechanical analysis (dma). Infrared (ir) and electron spectroscopy are also employed. 

The logical approach to problem solving for rubber analysis at Polysar Ltd was described by Chu [73] (cf. Schemes 2.4 and 2.5). Systematic analysis involves sampling, elimination of interference and measurement. Methods employed include chromatography (GC, HS-GC, HPLC, SEC, IC), spectroscopy (AAS, UV/VIS, IR, NMR), MS, microscopy and thermal analysis. The specific role of each of these techniques for the analysis of rubber compounds with or without... 

Selection of on-site analytical techniques involves evaluation of many factors including the specific objectives of this work. Numerous instrumental techniques, GC, GC-MS, GC-MS-TEA, HPLC, HPLC-MS-MS, IR, FTIR, Raman, GC-FTIR, NMR, IMS, HPLC-UV-IMS, TOF, IC, CE, etc., have been employed for their laboratory-based determination. Most, however, do not meet on-site analysis criteria, (i.e., are not transportable or truly field portable, are incapable of analyzing the entire suite of analytes, cannot detect multiple analytes compounded with environmental constituents, or have low selectivity and sensitivity). Therefore, there exists no single technique that can detect all the compounds and there are only a few techniques exist that can be fielded. The most favored, portable, hand-held instrumental technique is ion mobility spectrometry (IMS), but limitations in that only a small subset of compounds, the inherent difficulty with numerous false positives (e.g., diesel fumes, etc.), and the length of time it takes to clear the IMS back to background are just two of its many drawbacks. 

Another phosphorus containing CDA (87) has also been described for the estimation of the enantiomeric excess of chiral amines80. The phosphorus CDA 87 is formed quantitatively and instantaneously in situ in an NMR tube by reaction of phosphorus trichloride (PCI3) with the chiral diamine 88. Addition to the NMR tube of the chiral amine (IC-NIIo) for which the ee is to be determined gives the diastereomeric phosphorous derivatives ... 

The N NMR chemical shifts of the axial/equatorial nitrogen atoms in isomers 1 and 2 (R = R = H NR2 = NH2, NMe2) proved useful for conformational analysis (lb, 2b) (82JOC1933). In case of NR2 = NMe2, the chemical shift sequence is reversed (Ic, 2c in Scheme 2) (82JOC1933). 

The deshielding of the resonance in lithium carbenoids is explained by the polarization of the elongated C—X bond and shows that the carbocationic structures Ic and 2c have to be taken into account. The postulated high s character of the C—Li bond is also confirmed by the NMR-spectroscopic investigations insofar as enhanced C- Li coupling constants have been observed in lithium carbenoids . Thus, the effect of the metalation that leads to the formation of lithium carbenoids can be summarized as follows (Scheme 3) . 

The H-NMR spectra of pavines can provide appreciable assistance in structural elucidation. The oxygenation pattern of a pavine may be deduced from a careful examination of the methine (H j) and methylene (H. f) proton absorptions (Ic). In the case of 2,3,8,9 substitution, the abc and def protons furnish two superimposable ABX patterns. A doublet integrating for two protons at the lower field end of the system at approximately 8 4.0 represents the bridgehead protons, Ha and Hj. At 60 MHz, it appears as if these protons are coupled to only one of the neighboring protons (J = 6 Hz) (18,20,25). Furthermore, the geminal hydrogens couple to each other with a coupling constant of 17 Hz (18,20). On... 

Bei den Alkyl-a-D-l5 opyranosiden sollten nach Reeves sowohl die Cl- als auch die IC-Form im Gleichgewicht vorliegen >. Das NMR-Spektmm des Benzyl-a-D-l5ncopyranosids (86) spricht fiirdas Oberwiegen... 

The spectral data provide information about the structure of a-acetoxydibenzylnitrosamine (VII). The high frequency (1780 cm ) for the carbonyl group in the infrared spectrum (Fig. 9) is consistent with this structure ( ) and the introduction of the chiral center at the benzylic position causes the methylene of the other benzyl ic substituent to be diastereotopic and appear in the nmr spectrum as an AB quartet. The center of the quartet... 

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