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[摘要]：The geometries of a series of [n](2,7)pyrenophanes (n = 6-12) were optimized at the B3LYP/6-311G** DFT level. The X-ray crystal structures detd. for the [9](2,7)- and [10](2,7)pyrenophanes agreed excellently with the computed structures. The degree of nonplanarity of the pyrene moiety depends on the no. of CH2 groups in the aliph. bridge and, as analyzed theor., influences the strain energy and the extent of p-electron delocalization in the pyrene fragment. Various indexes, e.g., the relative arom. stabilization energies (DASE), magnetic susceptibility exaltations (L), nucleus-independent chem. were used to quantify the change in arom. character of the pyrene were evaluated by homodesmotic equations comparing the bent pyrene unit with its bent quinoid dimethylene-substituted analog. The bend angle, a, DASE, and L were linearly related. The aromaticity decreases smoothly and regularly over a wide range of bending, but the magnitude of the change is not large. The differences between planar pyrene (a = 0? and the most distorted pyrene unit (a = 39.7?in [6](2,7)pyrenophane) are only 15.8 kcal/mol (DASE) and 18.8 cgs-ppm (L). Also, the geometry-based HOMA descriptor changes by only 0.07 unit. The local NICS descriptors of arom. character also correlate very well with the global indexes of aromaticity. In line with the known reactivity of pyrenophanes, the variations of NICS(1), a measure of p-electron delocalization, were largest for the outer, biphenyl-type rings. The strain energies of the pyrene fragments were much larger and varied more than those evaluated for the bridge. Both strain energies were interrelated (correlation coeff. R = 0.979) and depend on the bend angle, a. |
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