We have determined the inhibition strength of a group of difunctional naphthalene-l-sulfonic acid esters. In these structures the sulfonic acid groups were placed at increasing distances from each other by using aromatic dihydroxy compounds as spacers. At short distances the inhibition factors of the difunctional compounds are much smaller than the sum of the inhibition factors of the monofunctional sulfonic acid groups, and we interpret this as the result of interference between the phenolic strings emanating from the S=O dipoles of the sulfonic acid moieties. By systematically increasing the distance between the sulfonic acid groups, we were able to determine the critical distance at which their strings no longer influence each other. We believe that in this way we have found the radius of gyration and hence the length of the undisturbed strings.