^aDepartment of Chemistry, Imperial College of Science, Technology and Medicine, London, SW7 2AY, UK.

^bChemistry and Engineering Group, MRC Cyclotron Unit, Imperial College School of Medicine, Hammersmith Hospital, Ducane Road, London, W12 0HS UK.

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Supplemental Information

How to make use of this Supplemental Information

The 3D molecular coordinates embedded within this supplemental data are best viewed using a browser plugin such as Chime (Version 2.0) (http://www.mdli.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 2.0. 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/distance or angle. Release the menu and click at the position of two (three) atoms. The value of the bond length or angle is displayed in the information box at the bottom of the browser.

Saving coordinates

Any set of coordinates can be saved onto your local disk for loading into other modelling programs.

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This supplemental data (c) H. S. Rzepa and S. Martin-Santamaria, 2000.

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Table 1. Energies (Hartree), polymerisation or activation energy (kcal mol^-1) and imaginary normal mode wavenumber (cm^-1) for stationary point structures 1-5 at five different levels of theory.

Entry	Ground Statea	Association energy per unit	Transition state for F-R extrusiona	n1
1, X1=X2=H, Y1=Y2=H	-14276.7220 (18.2) -14275.5576 (14.1) -14284.9882 (24.3) -14283.8232 (19.9) -14346.2180 (13.9) 192.8 (21.2)	9.1 7.1 12.2 10.0 7.0 10.6	-14276.6557 (41.6) -14275.4873 (44.1) -14284.9473 (25.7) -14283.7808 (26.6) -14346.1794 (24.2) 247.7 (54.8)	583 i 652 i 418 i 489i 413 i 794 i
2, X1=X2=X3=H, Y1=Y2=Y3=H	-21415.1012 (38.7) -21413.3493 (29.2) -21427.5135 (56.1) -21425.7506 (39.7) 267.3 (53.7)	13.9 9.7 18.7 13.2 17.9	-21415.0461 (34.6) -21413.2816 (42.4) -21427.4748 (24.3) -21425.7147 (22.5) 328.3 (61.1)	438 i 600 i 267 i 416 i 769 i
3,b X1=X2=X3=OCH3, Y1=Y2=Y3=CN	-22028.5216 (40.5) 223.0 (52.9)	13.5 17.6	-22028.4729 (30.6) 277.2 (54.2)	419 i 726 i
4,b X1=X2=X3=CN, Y1=Y2=Y3=OCH3	-22028.5216 (56.0) 223.0 (61.1)	18.7 20.4	-22028.4475 (46.5) 282.6 (59.6)	502 i 788 i
5, X1=X2=X3 =X4=H, Y1=Y2=Y3 =Y4=H	-28553.4824 (60.5) -28551.1393 (43.3) -28570.0263 (80.0) -28567.6815 (61.8) 350.9 (77.1)	15.1 10.8 20.0 15.5 19.3	-28553.4211 (38.5) -28551.0672 (45.2) -28569.9773 (30.7) -28567.6395 (26.33) 413.3 (62.4)	476 i 506 i 402 i 352 i 765 i

^a At the levels of theory corresponding to RHF/3-21G(d), RHF/MIDI!, B3LYP/3-21G(d), B3LYP/MIDI!, B3LYP/DZVP and MNDOD/kcal mol^-1. ^b Relative transition state energy 3-4; +15.9, +5.4 kcal mol^-1.