Point Group. Isomerism. Electronic Structure

The nonlinear molecular structure (Cg symmetry, see e.g. [1]) was proved by microwave (MW) [2, 3] and infrared (IR) spectra [4] in the gas phase. It was also obtained by ab initio [5 to 9] and by semiempirical (INDC) calculations [10] and by the extended Huckel theory [11]. 

The electronic configuration of the HOF X A ground state, written in a presumed order of decreasing binding energy, is [5]. The order of the three 

Orbital energies from other ab initio calculations pertain to assumed bond lengths [9] or to the experimental geometry [13, 14]. Orbital energies were also calculated semiempirically by the extended Hiickel method [11], by CNDO [15], INDO [15, 16], MNDO [17], and SINDO [18] (symmetrically orthogonalized INDO, see [19]). 

Apparently, the lowest total energy was calculated by Murrell et al. [5], = 

The influence of surrounding dielectrics upon orbital and total energies of the solute HOF molecule was calculated [31]. 

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In his discussion of the valence isomerization of troponoids, Chapman > has pointed out that 2-, 3-, and 4-methoxytropones undergo different photochemical behavior. A possible function of the methoxy group may he visualized as providing stabilization for charge-separated excited states as shown in structures 1, 2, and 3. In 7 and 3 (produced by excitation of 2- and 4-methoxytropone, respectively) smooth electron redistribution is available for collapse to type B cyclization products as indicated by the arrows. The corresponding intermediate 2 from 3-meth-... 

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