Lewis acid catalysis of photochemical reactions. 4. Selective isomerization of cinnamic esters

Journal Article · Wed May 28 04:00:00 EDT 1986 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00271a033· OSTI ID:5532358

Lewis, F D; Oxman, J D; Gibson, L L; Hampsch, H L; Quillen, S L

The spectroscopic properties and photoisomerization reactions of several (E)- and (Z)-cinnamic esters, bis cinnamic esters, and model esters and lactones in the presence and absence of Lewis acids have been investigated. The use of Lewis acids such as BF/sub 3/ or EtAlCl/sub 2/ results in enhanced photoisomerization efficiency and a shift in the photoequilibrium toward the thermodynamically less stable Z isomer. Enhanced E ..-->.. Z photoisomerization results from selective excitation of ground-state ester-Lewis acid complexes. These complexes have been characterized by /sup 1/H NMR, ultraviolet, and fluorescence spectroscopies. The equilibrium constants for complexation are dependent upon both the electron donor strength of the ester and its conformational mobility. These factors also determine the magnitude of the red shifts in the electronic absorption spectra observed upon complexation. Enhanced E ..-->.. Z photoisomerization upon complex formation is a consequence of selective excitation of the E vs. Z complex, more efficient isomerization of the excited E vs. Z complex, and larger equilibrium constants for complexation of E vs. Z esters. The photoequilibria obtained for bis cinnamic esters are highly enriched in the Z,Z and Z,E isomers in accord with independent isomerization of the two cinnamate groups; however, in the case of 1,3-trimethylenebis(cinnamate), two-bond isomerization of the E,E to Z,Z isomer is observed at low conversions.

• Research Organization: Northwestern Univ., Evanston, IL
• OSTI ID: 5532358
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 108:11; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400301 -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
400500* -- Photochemistry
ABSORPTION SPECTROSCOPY
CARBOXYLIC ACIDS
CATALYSIS
CATALYSTS
CATALYTIC EFFECTS
CHEMICAL REACTIONS
CINNAMIC ACID
DATA
EFFICIENCY
EMISSION SPECTROSCOPY
ESTERS
EXPERIMENTAL DATA
FLUORESCENCE SPECTROSCOPY
HYDROGEN COMPOUNDS
INFORMATION
INORGANIC ACIDS
ISOMERIZATION
ISOMERS
LEWIS ACIDS
MAGNETIC RESONANCE
MONOCARBOXYLIC ACIDS
NMR SPECTRA
NUCLEAR MAGNETIC RESONANCE
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
PHOTOCHEMICAL REACTIONS
QUANTUM EFFICIENCY
RESONANCE
SPECTRA
SPECTROSCOPY
THERMODYNAMICS
ULTRAVIOLET SPECTRA