Alternant X2Y2 (X = N, P, As, and Sb and, Y = O, S, Se, and Te) cyclic planar and butterfly like isomers have been studied at the complete-active-space self-consistent-field (CASSCF) molecular orbital and second-order configuration-interaction (SOCI) levels of theory with optimized basis sets including f-functions. The salient geometrical features, and trends in the intraanular X-X bond are discussed along with the relative energies between the isomers. Rationalization of the trends found in the relative energy is based on examining the various forms and magnitudes of bond strain present in each isomer.