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Azo Bridges from Azines, XXII. [2 + 2] Photocycloaddition and 1,5‐Laticyclic Conjugation Between Parallel Azo Groups and π‐Systems The Symmetry Criterion in Azo‐Carbonyl Interactions
Author(s) -
Brand Uwe,
Hünig Siegfried,
Martin HansDieter,
Mayer Bernhard
Publication year - 1996
Publication title -
liebigs annalen
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 0947-3440
DOI - 10.1002/jlac.199619960910
Subject(s) - bathochromic shift , hypsochromic shift , chemistry , excitation , photochemistry , blueshift , crystallography , stereochemistry , photoluminescence , fluorescence , physics , quantum mechanics , electrical engineering , engineering , optics
The known 1,5‐lacticyclic interaction between parallel CC/ NN bridges in 1 in expressed by a bathochromic shift of the azo n‐π * transition of +7–10 nm. A CCCN bridge ( 2, 6 ) increases the bathochromic shift slightly, whereas a CC–OSiR 3 bridge ( 3 ) cases a hypsochromic shift of −6 nm. In a R 3 SiO–C = C–CN bridge ( 4 ) the effect of the two substituents cancel each other. All these compounds ( 1–6, 13 ) undergo quantitative [2 + 2] photocycloaddition by n‐π * excitation. A novel transannular interaction between azo and carbonyl ( 20, 21 : +8 nm) and 1,2‐dicarbonyl groups ( 24 : ca. +20 nm) is observed. From photoelectron spectra and MO calculations neighboring group effects on the orbital energies in 20, 21 , and 24 are assessed and discussed.