title: Factor analysis of deuterium isotope effects on 13C NMR chemical shifts in Schiff bases.
abstract: We have analyzed deuterium isotope effects on (13)C chemical shifts in a series of o-hydroxy Schiff bases by applying factor analysis. Two orthogonal factors were obtained that explain about 80 and 10 % of the variance of the data. The numerical values of these factors can be related to 1H NMR chemical shifts of the proton involved in the intramolecular bonds delta(XH) (X = O or N). Such a relation allows one to identify clusters of compounds with different tautomeric forms of hydrogen bonding. Application of a similar approach to solution 13C NMR chemical shifts produces three important factors, which have a different structure to factors describing isotope effects. This illustrates well the different nature of chemical shifts and isotope effects. The three factors explain about 54, 15, and 13 % of variance. They can be rationalized and are strongly related to the electronic properties and location of substituents.
authors.affiliation: Chemistry Department, Warsaw University, Warszawa, Poland.
authors.forename: Paulina M
authors.initials: PM
authors.lastname: Dominiak
authors.forename: Aleksander
authors.initials: A
authors.lastname: Filarowski
authors.forename: Poul Erik
authors.initials: PE
authors.lastname: Hansen
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Woźniak