Structures and tautomeric interconversions of anthraquinone imine derivativesстатья
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Аннотация:Substituted 1-hydroxy-9,10-anthraquinone-9-imines have been found to exhibit tautomeric interconversions between the 9,10- and 1,10-quinonoid forms in the solid state as well as in solution. Single-crystal X-ray crystallography was used to study the structures of 4-(N-acetyl-p-tolylamino)-9-amino-1, 10-anthracenedione and 4-hydroxy-1-phenylamino-10-mesitylimino-9(10H)-anthracenone at ambient and low temperatures. The former compound gave crystals belonging to the monoclinic space group P2(1)/c and, at 295 K, a = 9.684(2), b = 16.371(3), c = 12.097(2) Angstrom, beta = 110.41(1)degrees, V = 1797 Angstrom(3), Z = 4, R(F) = 0.042, and GOF = 0.863. The latter compound gave crystals belonging to the monoclinic space group C2/c and, at 295 K, a = 38.158(8), b = 6.322(2), c = 19.325(4) Angstrom, beta = 101.78(2)degrees, V = 4564 Angstrom 3, Z = 8, R(F) = 0.052, and GOF = 0.981, while at 150 K, a = 37.852(6), b = 6.245(1), c = 19.235(4) Angstrom, beta = 102.81(1)degrees, V = 4434 Angstrom 3, R(F) = 0.047, and GOF = 1.006. Comparison of the geometric parameters of the two compounds illustrates the considerable zwitterionic nature of the first, a distinctive feature of which is a very short bond N(9)-C(9) whose length is essentially equal to that of a double bond. Molecular modeling studies using AMI semiempirical calculations were shown to be capable of satisfactorily reproducing the energetics of the tautomeric equilibrium once the medium effect was taken into account.