Abstract
TAUTOMERISM beween methyl-acenes (I, II, III, IV, V) and methylene-dihydroacenes (la, Ila, IIIa, IVa, Va, respectively) has often been postulated to explain side -chain reactivity of aromatic compounds but hitherto no methylene-dihydroacene has beprt isolated. This weakness in the hypothesis has rfow been removed by the synthesis of pure 6-methylene-6 : 13-dihydropentacene (Va). The 'anellation principle'1 requires a gradual transition in properties in the acene series, and it may be inferred, therefore, that (IV), (III), (II) and (I) will also contain the corresponding methylene forms, but in decreasing proportions.
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References
Clar, E., "Aromatische Kohlenwasserstoffe", 20 (Springer-Verlag, 1941).
Sirkin, J. K., and Diatkina, M. E., Bull. Acad. Sci. U.R.S.S., Cl. Sci. Chim., 153 (1946). Brit. Abstr., AI, 365 (1946). The view of these authors was supported, and in some cases an even greater stability of the higher methyl-acenes was predicted in private communications from other workers.
Ber., 56, 1619 (1923).
Clar, E., Ber., 75, 1271 (1942). Compare Fieser, L. F., J. Amer. Chem. Soc., 53, 2329 (1931).
Marschalk, Ch., Bull. Soc. Chim., (5), 4, 1549 (1937).
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CLAR, E., WRIGHT, J. Equilibrium Between Methyl-Acences and Methylenedihydroacenes. Nature 163, 921–922 (1949). https://doi.org/10.1038/163921a0
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DOI: https://doi.org/10.1038/163921a0
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