Supplementary material (ESI) for Perkin Transactions 2

This journal is The Royal Society of Chemistry 2002

Supplemental Information

Möbius Aromatic Forms of 8-p Electron Heteropines

William L. Karney,a * Christian J. Kastrup,b Steven P. Oldfieldb and Henry S. Rzepab *

aDepartment of Chemistry, University of San Francisco, California, 2130 Fulton St., San Francisco, California, USA, 94117-1080, USA. bDepartment of Chemistry, Imperial College of Science Technology and Medicine, London, SW7 2AY
Summary: Ab initio calculations at the B3LYP//6-31G(d) level predict that Möbius-like conformations of O, NF, S and PF-substituted 7-membered ring 8-p electron perfluoro-annulenes with an axis of symmetry exist, but they are of higher energy than isomers with a plane of symmetry. Chiral inversion of the Möbius perfluoroazepine system via a planar structure is shown to be an orbital symmetry forbidden process for a closed shell singlet state, resulting from the nodal characteristics of the highest occupied Möbius molecular orbital. The orbital origins of an unusual electron-correlation dependent lengthening predicted for the N-F bond in the Möbius conformation of the azepine but largely absent in the analogous phosphorus system are discussed. Structural variations based on incorporating a biphenyl motif are explored, but in no case was the Möbius form lower in energy than the achiral non-aromatic geometries retaining a plane of symmetry.
Graphical Abstract

How to make use of this Supplemental Information

1. All Coordinates are available as MDL Molfiles. These 3D molecular coordinates embedded within this supplemental data are best viewed using a browser plugin such as Chime (http://www.mdlchime.com/) or Chem3D Std or Net Plugin (http://www.camsoft.com/). To measure bond length or angles, proceed as follows:
Using Chem3D plugin, select an atom by mouse clicking on it. To measure a distance, move the cursor to the second atom, and the distance will be displayed on the screen. To measure an angle, select the first atom, and then by holding the shift key down, the second. Move the cursor to the third atom to display the angle on the screen.
Using Chime. From the pull down menu that appears when the mouse button is held down over the molecule (Mac) or the right hand mouse button is selected (Windows), go to Select/Mouse Click Action/ dihedral angle. Release the menu and click at the position of two (three) atoms. The value of the bond angle is displayed in the information box at the bottom of the browser. Due to an error in Chime, we regret that Bond lengths are displayed incorrectly, and should be measured using alternative programs. Any set of coordinates can be saved onto your local disk for loading into other modelling programs.

2. To demonstrate the 3D nature of the orbitals, each thumbnail image below is linked to a 3DMF file. To view these orbital models, you will need a 3DMF viewer such as the Quick3D or 3DMFPlugin (both browser plugins), 3DMF Optimizer (a Macintosh application), Geo3D (for Mac) or 3DMF Viewer for Windows. Windows users must also install the QuickDraw3D libraries from Apple.
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Table 1. Energies, kcal mol-1, relative to 2 or 4 (B3LYP/6-31G(d) in Hartree) and computed NICS Values (ppm).
System Point Group C=C
configuration
Negative
Roots
Dihedral angle
C3-C4-C5-C6
Relative Energy (2 or 4
in parentheses)
NICS(0)
1a Cs cis,cis,cis 0 0 2.6 (-902.7656) -5.7
1a C2 cis,trans,cis 0 94.8 36.3 -10.5
1a C2v cis,cis,cis 1a 0.0 14.5 +9.4
1b Cs cis,cis,cis 0 0 4.7 (-1225.7418) -8.0
1b C2 cis,trans,cis 0 107.7 36.7 -10.9
1b C2v cis,cis,cis 1b 0.0 21.3 +7.3
1c Cs cis,cis,cis 0 0 -21.3 {-24.7}g (-982.0395) -9.5
1c C2 cis,cis,cis (7c) 0 32.4 4.9 {-1.1}g -6.6
1c C1 cis,trans,cis 0 98.1 23.9 -10.7
1c C2v cis,cis,cis (5c) 2c 0.0 14.1 17.5
1c C2v cis,cis,cis (8c) 2d 0.0 27.8 {4.2}g -
1d Cs cis,cis,cis 0 0 -11.4 {-9.8}g (-1268.7453) -7.9
1d C2 cis,cis,cis (7d) 0 43.9 46.0 {47.7}g -10.9
1d C1 cis,trans,cis 0 111.0 23.0 -6.5
1d C2v cis,cis,cis (6d) 3e 0.0 81.9 53.4
1d C2v cis,cis,cis (8d) 3f 0.0 67.0 {63.1}g -8.5
3a C2 cis,cis,cis 0 39.4 40.5 (-614.7114) 26.5, -1.1h
3b C2 cis,cis,cis 0 42.7 25.5 (-799.1745) 16.5, -3.1h
3c C2 cis,cis,cis 0 53.8 46.2 (-937.7039) 14.9, -4.0h
3d C2 cis,cis,cis 0 41.2 19.3 (-594.8438) 20.8,-1.0h
3e C2 cis,cis,cis 0 58.4 52.6 (-881.4595) 8.2, -6.2h
3f C2 cis,cis,cis 0 60.2 34.6 (-1065.9222) 4.0, -7.7h
aNegative root of Hessian; 118.8i cm-1 corresponding to Cs distortion. b89.4i cm-1 corresponding to Cs distortion. c472.0i, 115.8i cm-1 corresponding to Cs distortions. d59i corresponding to in-plane N-F bending) and 54i cm-1 corresponding to C2 distortion. e382.7i and 119.3i cm-1 corresponding to C2 distortions and 270.9i corresponding to Cs distortion. f 495.3i cm-1 (b1) corresponding to Cs distortion, 205.4i cm-1 (b2) corresponding in-plane P-F bending and 62.8i cm-1 (a2) corresponding to C2 distortion. g SCRF(DPCM) Solvation model.h Value for 6-ring.

Figures

Figure 1. B3LYP/6-31G* bond lengths (Å) for stationary points for perfluoro-oxepine and perfluoro-thiepine.


Figure 2. B3LYP/6-31G* bond lengths (Å) for isomers of perfluoro-azepine.

Figure 3. B3LYP/6-31G* Orbital Correlations for 5c, 7c and 8c.
5c Symmetry 7c 8c Symmetry
a2 a b1
b1 a a2
a1 b a1
a1 a a2
a2 b b1
HOMO-LUMO gap
b1 a b1
a2 a a1
b1 b a2
b1 b a1
b1 b b1
a1 a b1

Figure 4. B3LYP/6-31G* bond lengths (Angstroms) for for stationary points for 1d.

Figure 5. B3LYP/6-31G* Orbital Correlations for 6d, 7d and 8d
5d Symmetry 6d 7d Symmetry
a2 b a2
b1 a b1
b1 b b1
HOMO-LUMO gap
a2 a a1
a2 a b1
b1 b a2
b1 b b1
b1 b b1

Figure 6. A relaxed B3LYP/6-31G potential scan in C2 symmetry connecting 7d and 8d. The dihedral angle is defined as C4-Du-P-C2, where Du is the mid-point of C4-C5.
Variation of bond lengths with twist
Figure 7. B3LYP/6-31G* Highest occupied Molecular Orbital for 3d.
HOMO