- For alternant I-network Systems both heteroatoms and system size have been imagined to influence ground-state spin multiplicities. Here theoretical and computational evidences are presented against a significant influence of system size and in favor of a notable influence of heteroatoms. Pair-excitation limited configuration interaction (CI) is argued to exhibit artifactual system size effects, so that other computational schemes are recommended to predict Splitting patterns of weakly coupled electrons. Full CI computations are reported illustrating the influence of heteratom electronegativity on the Splitting pattern of a couple -network structures. 1993, Taylor & Francis Group, LLC. All rights reserved.