A field may be interrupted by other bonds or atoms before propagating to a reactive site of interest.[6] Atoms of differing electronegativities can move closer together resulting in bond polarization through space that mimics the inductive effect through bonds.[6] Bicycloheptane and bicyclooctane (seen left) are two compounds in which the change in acidity with substitution was attributed to the field effect.[4] The C-X dipole is oriented away from the carboxylic acid group, and can draw electron density away because the molecule center is empty, with a low dielectric constant, so the electric field is able to propagate with minimal resistance.[5]