Transmission of substituent effect through π-conjugation by cyclobutane ring

A simple mathematical approach is provided in this article about the sp2 character of the carbons of cyclobutane and its ability to transmit substituent effect through pi-conjugation comparing the Hammett reaction constants (rho) of the dissociation equilibriums of cinnamic acids, 2-(3 or 4-X-phenyl)cyclobutane-1-carboxylic acids and 3-phenylpropionic acids.Graphical abstractThe substituent (X) effect on dissociation equilibriums of 2-(3 or 4-X-phenyl)-cyclobutane-1-carboxylic acids through pi-conjugation by cyclobutane ring is demonstrated comparing its Hammett reaction constant (rho) with those of 3-X-phenylpropionic acids and cinnamic acids. The substituent effect in 2-(3 or 4-X-phenyl)-cyclobutane-1-carboxylic acids is 18% as effective as cinnamic acids.