To have insight into the structure, strain energy and -conjugation / aromaticity of 5a-c, computational studies were conducted by the DFT method with the Gaussian 16 package. To simplify the calculation, all N-alkyl substituents are replaced by methyl group. Geometry optimization by B3LYP functional with the 6-311G(d) basis produced belt structures obtained in single crystal X-ray diffraction analysis. Following a literature method, an equation of Estrain = 213.91×n×e -n/2.5 (Kcal/mol) was established to estimate the total strain energy of belt [n]pyrrole [n]pyridines. Clearly, strain energy increases exponentially with the decrease of the number of the repeat units (n) of the belts (Fig. ). A high strain energy of 116.4 Kcal/mol for 5a well explained the low chemical yield (5%) of its synthesis even though the macrocyclic precursor 4a adopted a favorable predisposed conformation for fjord-stitching Caryl-Caryl bond homocoupling reactions (vide infra).