Organic chemistry allows for a basically infinite number of modifications of molecular structures. For example, substituents added to a molecule can lead to either a stronger or a weaker coupling to the substrate. We performed a comparative study of tetra-tert-butyl phthalocyanine (ttbPc) isomers on a Ag(111) surface by means of low-temperature scanning tunneling microscopy to analyze the influence of substituents on the tautomerization, a proton transfer reaction, in single molecules. By comparison with other well-studied molecules we find a decoupling of ttbPc from the surface. We find significant differences between the four ttbPc isomers which naturally exist due to different bonding positions of the tert-butyl groups on the macrocycle. The result has been published in the Journal of Physical Chemistry C.