A detailed exploration of the singlet potential surface for the system CHNO has been carried out with the aid of ab initio molecular orbital theory with minimal, split-valence, and split-valence + polarization basis sets. Direct search procedures are used to locate minima and transition states within the surface. The most stable isomer of CHNO is predicted to be isocyanic acid (HNCO) followed by cyanic acid (HOCN), formonitrile oxide (HCNO), and carboxime (HONC). Each of these isomers is predicted to be quite stable with respect to intramolecular rearrangement. HCNO is found to have a linear equilibrium geometry while HNCO, HOCN, and HONC are each predicted to have trans bent structures. It is shown that singlet formyl nitrene and the cyclic isomers of CHNO are unlikely to be observable species. The rearrangement of HCNO to HNCO proceeds via structures resembling oxazirine and formylnitrene; however, neither of these species is predicted to be an intermediate on the reaction path.One of the simplest typical "organic" molecules-containing the typical "organic" elements carbon, hydrogen, nitrogen, and oxygen-is the molecule with the empirical formula CHNO. Although reasonable valence structures may be drawn for at least seven CHNO isomers (Table I), relatively little is known experimentally about these compounds. Only two isomers, HNCO2 and HCNO,3 have been isolated in pure form and subjected to detailed spectroscopic examination. The substituted isomers RNCO,4 RCNO,5 and ROCN4 are more common, and substituted formylnitrenes RC(0)N have fre-

Ab initio molecular orbital theory has been used to study the ionization of methane, ethane, propane, n‐butane, isobutane, cyclopropane and cyclobutane. For methane radical cation, the preferred structure has C20 symmetry and a pair of long C—H bonds, resembling a complex of CH+2 with H2. This appears to be the only significant minimum on the CH+4 surface. For the remaining acyclic systems, the calculated structures of lowest energy (e.g., CH3‐CH2—CH+3, CH3‐CH2—CH2‐CH+3) are characterized by the extreme lengthening of a single C—C bond. However, alternative structures with two or more elongated C—C bonds have very low relative energies. The main structural conclusion for the alkane and cycloalkane radical cations is that the potential energy surface connecting various possible isomeric structures is generally very flat. Facile wide amplitude distortions and scrambling processes are therefore expected in these ions. The large structural changes which accompany ionization are manifested in large differences between vertical and adiabatic ionization potentials.

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Ab initio molecular orbital calculations with the STO-3G and 4-31G basis sets have been carried out for the radical anions of benzene (Bz-) and fluorobenzene (FBz-). In accordance with the Jahn-Teller theorem, Bzis predicted to distort from regular hexagonal (ZJ6*) symmetry. The best structures of Bzhave D2h symmetry. Two quite different £>2/i structures are found, one with four longer and two shorter C-C bonds and the other with two longer and four shorter C-C bonds. Configuration interaction calculations suggest that these two structures have very similar energies. Interconversion of equivalent Z)2/i structures requires little activation energy, a result consistent with the experimental ESR spectrum. The ring skeletons of FBzand Bzare similar suggesting that the Bzstructures might usefully serve as models in studies of radical anions of substituted benzenes.