Mesomeric betaines molecular orbital calculations

Among the variety of compounds emerging from prototype structures 10-28 mentioned in the Introduction (Table I), X-ray structural determinations have been performed on six representative examples the mesomeric betaines 55, 116, 117, and 120 the higher homologue 119 and the novel aza analogue of sesquifulvalene with a betaine character 118 (Scheme 9 and Table VIII). As mentioned earlier, the experimental dipole moments for molecules 55,116-119 were found to be in the range 9 to 13 D (III,B, Scheme 8 and Table Vll). Comparison of the experimental molecular geometries and dipole moment values with those obtained from semiempir-ical molecular orbital calculations is discussed below (III,D). 

The type of conjugation is also reflected in the frontier orbital profile, the charge distribution, and the permanent dipole moments. The results of semiempirical calculations on l-methylpyridinium-3-olate (16), Malloapeltine (17), Trigollenine (18), and Homarine (19) are presented in Scheme 7. Characteristically for the class of conjugated mesomeric betaines, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are distributed over the entire molecule as examplifled for l-methylpyridinium-3-olate. It was shown that 90% of the... 

Figure 1 ir-Molecular orbitals of representative heteropentalene mesomeric betaines calculated using the Huckel... 

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See also in sourсe #XX -- [ , ]

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