15678-54-3Relevant articles and documents
Preparation and structure elucidation by NMR of the charge delocalised β,β-carotene dication
Lutnaes, Bjart Frode,Bru?s, Liv,Krane, Jostein,Liaaen-Jensen, Synn?ve
, p. 5149 - 5152 (2002)
The β,β-carotene dication (λmax 985 nm at room temperature) prepared by treatment of β,β-carotene with BF3-etherate had considerable stability. The reaction, monitored by EPR studies at -25°C, occurred by free radical intermediates. EIMS further revealed a C40H56BF3 intermediate. The detailed structure of the charge delocalised β,β-carotene dication was established by COSY, HSQC, HMBC and 1D and 2D ROESY NMR techniques (600 MHz, CDCl3, -25°C) leading to complete assignments of 1H and 13C chemical shifts and 3JH,H coupling constants. Considerable downfield shifts were observed relative to β,β-carotene. The results are consistent with charge delocalisation mainly in the C-5-C-9 and C-5′-C-9′ regions and with retro shifted double bonds in the central C-13-C-13′ region. The effect of the two delocalised charges on chemical shift (charge distribution) and bond distance (3JH,H) is discussed.
