Stable geometrical structures for formonitrile imine (1) and N-substituted nitrile imines HCN2 R (R = Li, BeH, BH2, CH3, CN, CCH, C6H5, NH2, OH, and F) (2-11) were examined by using the multiconfiguration self-consistent-field (MCSCF) method followed by second-order configuration interaction (SOCI) calculations and second-order multiconfiguration quasi degenerate perturbation theory (MCQDPT2) calculations, together with the aug-cc-pVTZ basis sets. The results show that 1 suffers a pseudo-Jahn Teller (JT) distortion from a linear C-infinity v structure to a C-1 structure via a planar bent C-s structure. Each of the others is found to undergo pseudo JT distortion from a symmetrical structure to a planar bent C, structure for 2, 3, and 7 and to a C-1 structure for 4, 5, 6, 8, 9, 10, and 11. At the stationary structures of 1-11, the structural characteristics were briefly discussed in terms of allenic and propargylic. To elucidate the nature of pseudo JT distortions, energy component analyses were carried out at the MCSCF+SOCI level of theory at all of the stationary structures for the relevant molecules. In most of the molecules examined, pseudo JT stabilizations were classified into two groups, one in which the stability arises from a lowering of the energy of the attractive term V-en and the other in which the stability results from a lowering of the energy of the repulsive terms V-nn and V-ee. In addition to the above two groups, it was also found that the following three groups are responsible for the pseudo-JT stabilizations in a certain stage of the structural changes. Namely, one is a lowering of the energy of the term V-ee observed in 6, another is a lowering of the energy of the terms V-ee and V-en observed in 9-11, and the other is a lowering of the energy of the terms V-en and V-nn observed in 10. These energetic behaviors were accounted in terms of an elongation or a contraction of the molecular skeleton, a migration of electrons from one part of the molecule to other parts, and the combined effects arising from these two factors.