CNMR

All nuclei with an odd mass number have a fractional (1/2, 3/2, etc.) spin number. Also, all nuclei with an even mass nnmber and an odd atomic number have a unit (1, 2, 3, etc.) spin 

However, it can be seen readily that essentially all other elements have at least one isotope that can be examined by NMR. Examples were given in Table 3.1, and some additional isotopes are listed in Table 3.5, together with their sensitivity by NMR compared to the proton. 

NMR is now a routine technique, providing important structural information about the carbon backbone of organic molecules. 

Coupling between C and H nuclei does occur, but there are techniques available to decouple these nuclei. Consequently, the C NMR spectra are very simple, with a singlet seen for each chanically distinct carbon atom. This facilitates interpretation of the spectra And, as we will see later, the comparison of C and H spectra leads to data that can be interpreted with a high degree 

Nucleus Natural Abundance (%) Spin Sensitivity Relative to 

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The same reaction performed in ether at 0°C (336) gives the same major adduct, but the structure proposed by Acheson et al. corresponds to 86, although such a structure is hardly compatible with the presence of an isolated low-field proton. Very recently, in a reinvestigation of these cyclo-additions of DMA to azoles (338, 339), Acheson et al. were able to establish the correct structure of the adducts on the base of CNMR spectra and X-ray diffraction studies. The adduct of thiazole is represented by formula 87, and it results from the rearrangement of the... 

Calculated rr-bond orders are summarized in Table 1. These calculations are supported by chemical evidence that the S—N bond is the one most easily cleaved. Attempts have been made to relate bond orders and electron densities to NMR coupling constants (74CJC833, 77aC6i9> and CNMR (75CJC596, 75CJC1677> and NNMR (78JOC4693> chemical shifts, with limited success. 

The CNMR chemical shifts of a number of substituted isothiazoles and 2,1-... 

Some results have been published on 2-alkylisothiazole-3- and -5-thiones (75CJC836, 80JCS(P 1)2693). As expected, the resonance of the carbon attached to the exocyclic sulfur atom is shifted downfield, to around 185 p.p.m. in the case of the 3-thiones and to over 190p.p.m. for the 5-thione. It is possible that CNMR chemical shifts could be used to investigate tautomerism in related compounds. Saccharin has carbon resonances at 161.0 (3), 127.9 (3a), 125.1 (4), 134.7 and 135.5 (5 and-6), 121.2 (7) and 139.5 (7a) p.p.m. in DMSO solution <82UP41700>. 

The NMR chemical shifts of non-aromatic isothiazoles can be predicted with reasonable accuracy using standard substituent increments. A particular usefulness of NMR is its ability to distinguish between very similar compounds, and for this reason NMR finds application in pharmaceutical and other analyses. As an example CNMR allows ready distinction of the dlastereolsomers of dehydromethionine (14) and the possibility of detection of one dlastereolsomer in the presence of the other (79JOC2632). 

H-Dibenz[6/]azepine, 10,1 l-dihydro-5-niethyl- C NMR, 7, 498 <74JCS(P2)1648) 5H-Dibenz[r c]azepine H NMR, 7, 497 <81LA240) 6H-Dibenz[c,e]azepine, 6-allyl-5,7-dihydro- CNMR, 7, 498 <79JPS890) 5H-Dibenz[6,/]azepine-5-carboxylic acid, 10,11-dihydro-, ethyl ester C NMR, 7, 498 <74JCS(P2)1648)... 

Piperidine, 1-methyl- CNMR, 2, 15<76JA3778) dipole moment, 2, 160 <67JCS(B)493, 70JCS[Pg.42]

Pyrazole, 5-amino-3,4-dicyano-l -methyl- "CNMR, 5, 191 <75JOC1815)... 

Pyrazole, 5-amino-l,3-dimethyl- CNMR, 5, 191 <790MR<12)587, 79X12991)... 

Pyrazoline-5-thione, 2,3-dimethyl-1 -phenyl- CNMR, 5, 194 (74JHC135) 3-Pyrazoline-5-thione, 1,2,4-trimethyl-PE, 5, 205 (78JA1275)... 

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