Photoelectron spectra of ortho- and meta-substituted benzonorbornadienes. Relationships to regioselectivities in triplet di-.pi.-methane rearrangements

Control of regioselectivity in the di-.pi.-methane rearrangements. Triplet-sensitized photoisomerization of benzonorbornadienes carrying cyano substituents in the aryl and vinyl segments

“…We have shown earlier that the vacant orbital energies and shapes dominate bridging regioselectivity in benzonorbornadienes substituted on the aromatic ring by acceptor substituents. 18 In the case of the monocyano compounds, the LUMO polarization by the 2-cyano substituent in 10 is large, but not much larger than that caused by 5or 6-cyano substitution (Figure 9). However, the excited triplet state can only be described as a combination of two or more configurations, and the aromatic portion of the LUMO and SLUMO are polarized in an opposite fashion.…”

“…Hz, 1 H); m/e caled 292.9703, obsd 292.9710. 2.6-Dicyanobenzonorbornadiene (18). Vinyl iodide 20 (185 mg, 0.63 mmol) was heated with excess cuprous cyanide in HMPA in the manner described above.…”

Polar effects on di-.pi.-methane rearrangements. Regiospecificity in the triplet-sensitized photoisomerizations of 2-cyanobenzonorbornadienes carrying methoxy aryl substituents

“…The photoelectron spectra of the cyanomethoxybenzonorbornadienes are not reproduced here, since they are remarkably similar in appearance to those of the simpler ortho and meta methoxy compounds which we reported earlier. 6 The four lowest ionization potentials of the three isomers studied are shown in Figure 2, along with those of model systems to be discussed below. The first three IP's are due to the well-known benzonorbornadiene tr orbitals, while the fourth IP is due to an orbital heavily oxygen lone pair in character.…”

“…The third IP of 5-and 6-methoxybenzonorbornadiene arises from the orbital having the most olefinic tr character. 6 In these molecules, the vinyl cyano group has a delectably different influence on the IP's originating from orbitals heavily concentrated on the vinyl carbons, but the effect is very small. The methoxy group has a relatively large and specific effect on the IP's of benzonorbornadiene, and on the resultant shapes of the highest three tr molecular orbitals.…”

PE‐ und 13C‐NMR‐spektroskopische Untersuchungen zur Homokonjugation in 7‐Alkylidennorbornadienen

“…31 weist zwei Ionisierungsenergien bei Z, , , l = 8.55 eV und Z, , , 2 = 8.85 eV auf, die dem x-und einem osic(b2)-Orbital zugeordnet werden konnen. Zum Vergleich sei angefuhrt, daD in trans-l,2-Bis(trimethylsilyl)ethylen (4)…”