Empirical, equation structure refinement

Equations (4) and (5) have been empirically refined from a statistical survey of numerous crystal structures to account principally for the behavior of ribosides and 2 -deoxyribosides.4i However, similar modified equations have also been developed for sugars having other patterns of substituents (ara,xylo, and lyxo). The parameters characteristic for the ara-, xylo- and lyxo-configurations are phase-shifted by 120° with respect to either C-2 and C-3 of ribose. This is very important, given the fact that the experimental coupling constants have to be identified by PSEUROT as either cis or trans. For compounds 1—4 the modified equations published in ref. 42 were used. 

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