We report an experimental and theoretical study of the single-molecule conductance of two separate families of regioisomeric phthalocyanine derivatives in which the binding groups are connected at opposite or at contiguous positions about the phthalocyanine moiety. We observe that compounds with the longest distance between the anchoring groups yield molecular junctions with a higher conductance compared to those with a shorter distance. We performed both density functional theory (DFT) and tight binding calculations to understand how interference effects explain the experimental results including the role of constructive and destructive quantum interference in five phthalocyanine derivatives.