Variable-temperature NMR and X-ray crystallographic studies of 5-dimethylaminomethylene-, 5-dimethylaminopropenylidene-, and 5-(5-dimethylaminopenta-2,4-dienylidene)-derivatives of Meldrum's acid and related dimethyl malonate derivatives

Abstract

Variable-temperature ¹H and ¹³C NMR studies of the title Meldrum's acid derivatives and the corresponding malonates show in most cases coalescence phenomena due to C–N and CC rotation effects. The trends in free energies of activation for these processes are examined with respect to the X-ray crystal structures of the Meldrum's acid derivatives which show effects of electron delocalisation in the conjugated system.