Radical Anions of Sterically Protected Polyenes: An ESR and ENDOR Study

Facile Electron Uptake by Carotenoids Under Mild, Non‐Radiative Conditions: Formation of Carotenoid Anions

“…[44,45] General: NMR spectra were recorded on Bruker Avance 400 MHz and 600 MHz instruments in CDCl 3 with 0.05 % TMS as internal standard. The precise assignment of protons and carbons in the products was achieved by iterative interpretation of spectra from different NMR techniques ( 1 H, 13 C, DEPT, homo and hetero nuclear COSY, HMBC). UV/Vis spectra were obtained on a single beam Thermo Spectronic Helios γ and a HP 8453 diode array spectrometer.…”

“…When a solution of MeOK in MeOH was injected under nitrogen to DMSO or DMF in which 1 was dissolved, the color changed within 10 s resulting in a complete conversion (isosbestic point at 500 nm) from orange 1 (λ max = 450 nm) to a new blue product (λ max = 570 nm, Figure 1). Comparison of the 13 C NMR signals from the blue solutions in alkaline [D 6 ]DMSO with those of Car 1 (7 C=C) revealed a distinct up-shift of the polyene chain signals, which is indicative of a more electron rich molecule. It was identified as charged delocalized Car 2-3 (8 C=C) with the charge partially directed to oxygen (Figure 2, Scheme 1).…”

“…It was identified as charged delocalized Car 2-3 (8 C=C) with the charge partially directed to oxygen (Figure 2, Scheme 1). 13 C NMR signals of Car 2-3 compared to 13 C NMR signals of Car 1, upfield shift change expressed in % relative to Car 1.…”

“…[9] So far, electron uptake by Car has been investigated by quite elaborated methods: chemical reactions with metals (Al-Hg, Na, K, Cs), [10][11][12][13] and metal organic compounds (e.g. sBuLi), [14] electrochemical methods, [15] ionizing rays (pulse radiolysis) [2,16,17] and flash photolysis.…”

“…The broad shoulder at 700 nm could either indicate the presence of small amounts of long-wavelengths absorbing species or may be inherent to the electronic properties of 3. For NMR characterization 1 (10 mg, 0.034 mmol) was dissolved in deoxygenated [D 6 ]DMSO (1 mL) in 13 C NMR: δ = 165.86 ppm. The formation of 4 and formate is similar to the carbon dehomologation reaction of enamines.…”