An unusually stable dianion : cycloalkylidenemalononitrile dianion characterized by NMR, IR, MS & MNDO

The dianion of cyclopentylidenemalononitrile (CPDM2-) can be characterized by dialkylation. The adducts formed in diallylation have been studied both experimentally and theoretically. Diallyl-CPDM has been characterized by 1H and 13C NMR, IR spectrum and by its fragmentation pattern in the mass spectrum. The chemical reactivity of CPDM2- is easily explained or predicted using the frontier molecular orbitals, FMO, calculated using MNDO method. The evidences from NMR, IR, MS and the prediction from MNDO calculation were highly consistent. The results indicate a very stable dianion having a pattern of reactivity that is observed experimentally and predicts the isomeric structure of its alkylation product, Diallyl-CPDM (Isomer A), consistent with MS, IR and NMR experiments.Cyclohexylidenemalononitrile dianion (CHDM2-) has been generated by two dimetalating systems, n-butyllithium/DMSO and Dimsyl/DMSO, and examined by 1H and 13C NMR in DMSO-d6. The 13C NMR spectra of CHDM2- has been interpreted by means of MNDO atomic charge, attached proton test APT, Nuclear Overhauser Effect and chemical shift reference data. The generation of this dianion is accompanied by appropriately characteristic changes in the 13C chemical shifts.MNDO calculations have been performed for all molecules of interest, and found to be useful and reliable for the study of Y-conjugated dianionsof cycloalkylidene-malononitriles. The correlation of MNDO atomic charge vs empirical 13C chemical shift was found to be linear for sp2 conjugated carbons of negative-charged nitriles and the empirical equation, s = 44.9p + 125.4, predicts chemical shifts with only 2.14% average percent error. With FORCE calculation, MNDO method can calculate the frequencies of CPDM and CHDM with only 0.65% average error which was superior than AM1 method (3.87%). Moreover, systematic MNDO calculations of over 30 nitrile molecules have been carried out giving; heats of formation, electronic energy, core-core energy, dipole moment and ionization potential.The conformation of CHDM2- has been analyzed with MNDO optimized geometry and found to have 45° twist within the Y-conjugated n-system of the dianion. Double-LithiumBridging-Structure, the simple model of dilithio-CHDM, has been proposed based on Ion Triplets Theory and MNDO charge distribution, and its electronic energy was calculated from the distances of point charges in this model. The results indicate that the Li counterion can stabilize the dianion.Department of ChemistryThesis (M.S.