Characterization of methyl derivatives of cyclopentadiene monomer and dimer by 13C NMR spectroscopy

Abstract

AbstractThe assignment of the carbons of different isomers of methylcyclopentadiene monomers (Me‐CPD) and dimers (diMe‐DCPD) has been performed directly in a mixture, without previous separation of these products, by analysing data from quantitative 13C NMR spectra of the mixtures and applying a J‐modulated spin–echo sequence. Semi‐empirical rules for the influence of methyl groups on the chemical shifts of carbons in pentenic and norbornyl ring systems have been formulated and utilized to assign the absorptions. The same method can then be applied to the carbon assignments in cyclopentadiene–methylcyclopentadiene codimers (Me‐CPD), and it is possible to develop additivity rules and predict chemical shifts for diMe‐DCPD based on the chemical shifts for the carbons of these codimers.