Increment rules

In this second empirical approach, which has also been used for C NMR spectra, predictions are based on tabulated chemical shifts for classes of structures, and corrected with additive contributions from neighboring functional groups or substructures. Several tables have been compiled for different types of protons. Increment rules can be found in nearly any textbook on NMR spectroscopy. 

Further increment rules for the calculation of 13C shieldings in various types of saturated and unsaturated compounds may be found elsewhere (11). In a totally mathematical approach, Wiberg and co-workers (407,408) analyzed data for 18 sets of aliphatic and alicyclic halides (X = F, Cl, Br, or I) by means of factor analysis. They found that three parameter terms suffice to correlate all the shielding data ... 

Despite these significant differences in 13C chemical shifts, it may be problematic assigning the configuration of a given cyclopropane derivative if its diastereomeric counterpart is not available. Therefore, in order to predict 13C chemical shifts, increment rules have been derived which include cross-terms for pairwise interaction of bromine, methyl and ethynyl substituents425. This approach, however, requires an investigation of a large number of model compounds if further substituents are involved. 

H and 13C chemical shifts have been reported for many 1,2-disubstituted oxiranes432 436-439. Similar to cyclopropanes, oxirane ring carbon chemical shifts are smaller in the cis- than in the frans-isomers, and an increment rule using pairwise substituent interaction cross-terms has also been developed439. 

The discussion given earlier for weak mesomeric effects offers an explanation for the empirical increment rules proposed by Woodward (1942) for estimating the absorption maxima of dienes and trienes. The distinct values for the homo-and heteroannular arrangement of the double bonds illustrate the configurational influence on the polyene spectra that has been discussed in Example 2.2. From the data collected in Table 2.5 the absorption of methylenecyclo-hexene (27) with an exocyclic double bond and two alkyl substituents is calcu-... 

Table 2.5 Increment Rules for Diene Absorption (Adapted from Scott, 1964)...

The quaternary salts QX can be completely dissociated to free ions (Q+ and X ) in the aqueous phase (. [Q ]/[QX] > 100) and partially dissociated in the organic phase when the concentration of the quaternary salt is 0.0125 kmol/m. The quaternary salts QX can be partially dissociated to free ions in the aqueous and the organic phases when the concentration of quaternary salt is 0.1 kmol/m. The incremental rules of the dissociation degree of the quaternary salts were obtained as follows (1) increasing the charge-to-volume ratio of the central cation or counteranion (e.g., > N" " or 1 > Br > Cl ),... 

R. Stenutz, Automatic Spectrum Interpretation Based on Increment Rules CASPER , in Bioinformatics for Glycohiology and Glycomics An Introduction, eds. C.-W. Von der Lieth, T. Luetteke and M. Frank, John WUey Sons Ltd., Chichester, UK, 2009, p. 311. 

Increment rules that predict the chemical shifts of protons in the H n.m.r. spectra of aldohexopyranoses to within 0.09p.p.m. have been presented. 300 MHz H n.m.r. spectroscopy has shown that both a- and p-D-ribopyranose exist as a mixture of C4 and C, conformations in deuterium oxide, while P-d-ribo- and P-D-xylo-pyranosylamines prefer the C, conformation. The con-... 

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