Molecular structure paracyclophane

The crystal of 2 OPr recrystallized from EtOH/H20 solution, and the mixed crystal of the same ethyl and propyl cinnamate derivatives (2 OEt and 2 OPr), on photoirradiation for 2h at room temperature with a 500 W super-high-pressure Hg lamp, afforded the highly strained tricyclic [2.2] paracyclophane (2 OEt-2 OPr-cyclo) crystal quantitatively (Maekawa et ai, 1991b). A crystal structure analysis was carried out of a single crystal of the complex of 2 OEt-2 OPr-cyclo with HFIP (recrystallization solvent) in a 1 2 molar ratio. Fig. 13 shows the molecular structure of 2 OEt-2 OPr-cyclo viewed along the phenylene planes. The short non-bonded distances and deformation of the benzene rings, as seen in Fig. 13, are common to those of [2.2] paracyclophanes, as previously reported (Hope et ai, 1972a,b). 

The molecular structure of 1,2,9,10-tetragerma[2.2]paracyclophane 17 was determined by the X-ray diffraction study. The single crystals of 17 for X-ray crystallography were obtained from a toluene solution. Similar to 12, the crystal belongs to the space group P2Jn, and the data collection was carried out at 13°C. The ORTEP drawing of 17 is shown in Fig. 7. 

The synthesis of [2.2]paracyclophane (2) and its identification by X-ray structural analysis were first reported in a short communication by Brown and Farthing 8> in 1949. A more detailed report on its molecular structure followed in 19534>. Further investigations by Lonsdale et al.5> at two different temperatures (93 and 291 °K) provided additional information about the thermal expansion and molecular vibrations in the crystal. A recent X-ray structural analysis > confirms and supplements Lonsdale s observations. 

Contents J.Gasteiger, P.Gillespie, D.Marquarding, I.Ugi From van t Hoff to Unified Perspectives in Molecular Structure and Computer-Oriented Representation. - B.Vennesland Stereospecificity in Biology. - F.Vogtle, P.Neumann [2.23 Paracyclophanes, Structure and Dynamics. 

ABSTRACT. Crystal and molecular structures of (1 1) molecular complexes of N,N, N",N" -tetramethyl-2,ll,20,29-tetraaza[3.3.3.3]paracyclophane(] ) with CHCI3, CH2C12/ CH3CN and CO2 are reported. The macrocycle has square-box structure, giving hydrophobic cavity surrounded by four benzene rings. The guest molecules are included in the cavity. 

Similar behaviour has been observed in the photoreaction of methyl a-cyano-4-[2-(2-pyridyl)ethenyl]cinnamate (7 OMe) crystals in which the yield of [2.2] paracyclophane reached 65% on irradiation at — 78°C (see Scheme 10 p. 153) (Hasegawa et al., 1989b). From the crystal structure analysis of the same type of [2.2] paracyclophane, which is topochemically derived from alkyl a-cyano-4-[2-(4-pyridyl)ethenyl]cinnamate crystals, a highly strained molecular shape is confirmed in which two phenylene rings are severely bent (Maekawa et al., 1991b). 

The molecular and electronic structures are discussed on the basis of B3LYP and CASPT2 quantum chemical calculations. Paracyclophanes are attractive model compounds for studying specific intramolecular interactions [146, 147]. Gerson et al. [148] showed the radical anion of [2,2] paracyclophane 71 is an unassociated specie, with the unpaired electron being equally distributed over both 7r-systems. 

Such a rigorous proof of structure is still lacking for an equally interesting hydrocarbon with the molecular formula C60H38, which was isolated in 52% yield after subjecting a 1 2 mixture of 1,2-benzo [2.2]paracyclophane-1,9-diene (35) and its bromo derivative 36 to the same conditions as applied to 32 + 4. The NMR ( H and 13C) spectroscopic data, however, indicate a close structural analogy to 34 and suggest the constitution 37 for this product [30b]. Whether... 

As in the case of [6]paracyclophane (la), irradiation of [6](1,4)naph-thalenophane (55a) produced the Dewar type isomer 53a (s. Scheme 13) [40a]. In remarkable contrast, irradiation (X > 370 nm) of anthracenophane 56a did not give the Dewar type isomer 54a (s. Scheme 13) but yielded five stereoisomers of cyciobutane dimers 85 (Structure 13) [67], Four minor dimers have cis-cis junction around the cyciobutane ring, while the major product has ds-trans stereochemistry. This remarkable photochemical behavior of 56a is ascribed to the high double bond character of the bond a in the anthracenophane system, which is predicted by the semi-empirical molecular orbital calculations. 

Jagadeesh MN, Makur A, Chandrasekhar J (2000) The interplay of angle strain and aromaticity molecular and electronic structures of [0n]paracyclophanes. J Mol Model 6(2) 226-233... 

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