Aromaticity on the Edge of Chaos: An Ab initio study of the bimodal balance between aromatic and non-aromatic structures for 10-p-Dihetero[8]annulenes.

Henry S. Rzepa* and Nikola Sanderson

Department of Chemistry, Imperial College London, SW7 2AY

Summary: The computed geometries of a class of 10-p-annulenes containing two heteroatoms, which exhibit an acutely sensitive balance between p and s influences upon ring planarity, reveal that the recent KMLYP hybridisation of the exchange functional in the DFT method is qualitatively superior to the more commonly used B3LYP hybrid for modelling the aromaticity of such systems.

Graphical Abstract
Structures 1-6

Electronic Supplemental Information

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Table 1. Geometries, Energies and NICS values for 4 - 6.

B3LYP/KMLYP 6-31G(d) Energy, Hartree
NICS(0), ppm [B3LYP/KMLYP]		 Crystal Geometry:
length, Å
[dihedral, degrees]		 Geometry (B3LYP) Geometry (KMLYP)
4, X=Y=O, R=H
 -382.59901/ -381.82874 [-8.2/-7.3] planar [0.0/00.0]
4, X=Y=O17
-724.75782/-723.29019a,b [-7.5/0.1]		 CUWWEW-xray CUWWEW-b3lyp CUWWEW-kmlyp
4, X=Y=O17
955.53210/-954.11459 [-7.7/-7.0]		 XrayCUWWEW B3LYPCUWWEW
4, X=Y=NH18
-342.89994/-342.21433 [-12.9/-12.5]
 B3LYPCUWWEW B3LYPCUWWEW
4, X=Y=N-TMS18
-1160.27700/-1158.59120 [-11.3/-10.8]
 Reported as planar
4, X=Y=N-CONMe219
-837.52547/-835.89800 [-8.5/-6.0]
 Reported as planar
4, X=Y=NCO2Me19
-798.64839/-797.07613 [-6.0/-1.3]
4, X=Y=N-SO2Me18
-1518.65134/-1516.49681c,d [-9.6/-7.4]
 Reported as twisted
5, X=Y=N-Acetyl24
-1715.32163/-1712.39694 [-0.8/-0.6]
4, X=O, Y=N, R'=(3,4,5-trimethoxybenzyl)20
-976.66132/-974.75355 [-10.0/-9.2]
4, X=O, Y=N-Tosyl20
-1181.67739/-1179.74661e,f [-8.9/-7.6]
4, X=Y=S21
-1256.41893/-1254.75146 [-2.5/-2.4]
4, X=Y=S22
-1260.83295/-1259.16593 [-2.2/-2.0]
4, X=S, Y=O23
-2852.64265/-2849.43451 [-2.17/-2.1]
4, X=O, X=S
-705.57218/-704.57509g [-9.2/-1.2 ]		 unknown
4, X=CH-, X=S
-669.09512/-668.17759[-14.1/-14.6]
 Diatropic by NMR25
4, X=CH-, X=O -346.1104603/-345.4187586[-13.5/-13.5]
 Diatropic by NMR18
4, X=CH-, X=NH -326.249677/-325.60088 [-15.8/-16.3]
 Diatropic by NMR18
6, X=Y=Z=NH -320.79828/-320.16244 [-8.2/-7.4] Unknown 36.7 12.5
aCorrected for DG: -723.15206, Total energy (MP2): -722.61300 bPlanar valence isomer; total energy (KMLYP/MP2) -723.29133/722.61166. Corrected for DG(KMLYP): -723.14989, NICS(KMLYP) = -6.1. c Total energy (MP2): -1515.42207 d Non-planar isomer (MP2); -1515.42046, C3-X4-C5-C6 dihedral = 82.5o. e Corrected for DG: -1179.53934. Total energy (MP2); -1139.55775. fNon-planar isomer; total energy (KMLYP/MP2) -1179.74319/-1139.55812 Corrected for DG(KMLYP): -1179.53740. NICS(KMLYP) =-1.2. C3-X4-C5-C6 dihedral (KMLYP) = 82.5o. gValence isomers; total energy (B3LYP/KMLYP) -705.56747/-704.57398 [-1.6/-8.6]. Transition state for interconversion (KMLYP): -704.57242 [-4.1]

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