Abstract
The spectroscopic properties and thermal and photochemical isomerization reactions of (E)- and (Z)-β-furylacrylic and urocanic esters in the presence and absence of Lewis acids have been investigated. As is the case for cinnamic esters, complexation of β-furacrylic esters occurs on the carbonyl oxygen and results in a large red shift in the electronic absorption spectra and photostationary states enriched in the thermodynamically less stable Z isomer. Unlike cinnamic and β-furlacrylic esters, the Z isomer of methyl urocanate is more stable than the E isomer due to the formation of a moderately strong intramolecular hydrogen bond from the imidazole N1-H to the carbonyl oxygen. Complexation of both E- and Z-methyl urocanate with BF3 occurs on the imidazole N3 rather than carbonyl oxygen and causes a large blue-shift in their electronic absorption spectra. The free esters undergo reversible E,Z photoisomerization whereas their BF3 complexes undergo one-way E Z photoisomerization. The failure of the complexed (Z)-urocanate to photoisomerize is attributed to an increase in the intramolecular hydrogen bond strength upon complexation.
Original language | English (US) |
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Pages (from-to) | 5964-5968 |
Number of pages | 5 |
Journal | Journal of the American Chemical Society |
Volume | 108 |
Issue number | 19 |
DOIs | |
State | Published - Sep 1 1986 |
ASJC Scopus subject areas
- Catalysis
- Chemistry(all)
- Biochemistry
- Colloid and Surface Chemistry