Dicarbene quintet state

Encouraged by the experimental finding (Itoh, 1967 Wasserman et al., 1967) that the dicarbene [15 m = 2] ( = [3]) had a ground quintet state, i.e. all four spins were ferromagnetically coupled, Iwamura and Itoh have been engaged in a project directed towards the construction of the higher series of poly(carbenes) [15], [23] and [24] (Iwamura et al., 1985 Teki et al., 1983, 1985, 1986). 

Fig. 22 (a) Epr spectrum obtained by photolysis of the didiazo-compound o-[38a] of a [2.2]paracyclophane. (b) The signals due to unoriented dicarbene o-[38] in the quintet state simulated by a perturbation calculation. 

The thermal reactions of the DR-intermediates, however, exhibit an extraordinary effect. Hand in hand with the disappearance of the DR series a new series appears, which shows a four line ESR fine structure arising from S = 2 quintet dicarbene DC states 3-66) "pjje thermal transformation of the DR intermediates into the DC inter-... 

The chemistry of high-spin polycarbenes started in 1967 when two groups led by K. Itoh [1] and E. Wasserman [2] reported independently their findings that OT-phenylene-dicarbene Ic generated by the photolysis of diazo compound Id has a ground quintet state. Prior to this report, A. M. Trozzolo and coworkers... 

Figure 9.10 Temperature dependence of the ESR intensities of dicarbenes DC9, DCm, and DCn. The calculated lines have been fitted by Eq. 9 with the activation energies As q for the quintet states [33,47].

The first term of Eq. 4 represents the electronic Zeeman term, Si and 2 the spin operators for tvro triplet carbenes, and the second term represents the electronic exchange interaction. If Si and 2 couple to a quintet state (S = 2), ( 1 + 2) = S = S(S + 1) = 6. If they couple to a singlet, S = 0. Therefore, this term directly results in the energy level scheme, indicated in the inset of Fig. 9.13. The pure singlet and the pure quintet states are split by Assq which turns out to be the characteristic property of each dicarbene. The third term of Eq. 4 represents the magnetic dipole-dipole coupling of the two triplet carbenes ... 

For a long time it was unclear whether the triplet state (S = 1) of the dicarbenes ( DC) does exist, and if it does whether its energy is higher or lower than the energy Acsq of the dicar-bene quintet state ( DC). Miiller-Nawrath et al. [51] have shown theoretically and experimentally that the ESR transitions of the triplet states of carbenes ( C) and of dicarbenes ( DC), respectively, are mutually degenerated in diacetylene oligomers of diacetylene crystals if the... 

The results of these studies are summarised in Figure 5. For TS, the first intermediate observed is a dimer diradical, which can be converted thermally or by selective irradiation into a trimer, tetramer, etc.. Irradiation, however, also produces an asymmetric carbene trimer, which in turn can be converted into a series of oligomers. There is then a further side reaction which converts the asymmetric carbene trimer into a stable oligomer. Conversion of a diradical into an asymmetric carbene and a carbene into a stable oligomer occur only by the addition of a further monomer unit to the intermediate. These intermediates appear as the direct products of photo-polymerization below 80 K. Above K dicarbene radicals with singlet ground states and excited triplet and quintet states are observed. Some of these are sufficiently long for the interaction of the carbene radicals to... 

K. Itoh, Quintet state of dicarbene, Chem. Phys. Lett., 1, 235 (1967). 

It is possible to exactly identify and characterize the radical species and chain structures of the reaction intermediates, which are determined by their different reactive or unreactive chain ends. The reactive intermediates are best described by diradical (DR), asymmetric carbene (AC) and dicarbene (DC) oligomer molecules of different lengths. The respective singlet (S = 0), triplet (S = I) or quintet (S = 1) states and their roles in the polymerization process are investigated in detail by solid state spectroscopy. A one-dimensional electron gas model is successfully applied to the optical absorption series of the DR and AC intermediates as well as on the different stable oligomer SO molecules obtained after final chain termination reactions. 

Photolysis of (2-phenoxyphenyl)phenyldiazomethane (36) in cyclohexane at 10°C gave phenylcycloheptabenzofuran (37) via (2-phenoxyphenyl)phenylcarbene.The infrared spectrum of photo-chemically generated anthranylidene has been determined,and the dicarbene, (9,lO-dihydro-9,lO-o-benzeno-2,6-anthrylene)di(phenyl-methylene), has been shown by e.s.r. spectroscopy to have a quintet ground state.Products of photodecomposition 1,l-dimethyl-2-diazo-2-phenylethanol (38) in cyclohexane are the hydroxy ketone (39), the oxirane (40) and 3-phenylbutan-2-one (41), whereas reaction in methanol gave the methoxy alcohol (42) and the alkene (43).43... 

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