A dipole moment study of the structures of some ketene acetals

The dipole moments of several acyclic and cyclic ketene acetals have been determined in benzene solution at 293 K using the Halverstadt-Kumler method. For ketene dialkyl acetals (alkyl = Me, Et) the results point to a predominance of the s-cis,s-trans retamer, which disagrees with the conclusions drawn previously from ¹³C NMR chemical shift data, i.e. the s-cis,s-cis form is the more stable species. In the case of 2-methoxyfuran, the dipole moment measurements confirm the previous findings based on the ¹³C NMR spectra, viz the s-cis form is the predominating rotamer. The dipole moments and structures of some other ketene acetals are also discussed.