The use of nuclear magnetic resonance (nmr), infrared (ir), and mass spectra to determine the structures of disubstituted (aromatic) [2.2]paracyclophanes is described. Besides the usual chemical shift in the nmr observed for protons ortho to substituents, the following 4-substituted [2.2]paracyclophanes exhibit downfield shifts for their pseudo-gem protons:2 bromo, chloro, iodo, cyano, methyl, ethyl, hydroxy, acetoxy, and methoxy. The absorption appears as a doublet (J = 8 Hz) with further small splittings (1 to 2 Hz) due to ortho, meta, and para proton splittings. If either X or Y of X,Y-[2.2]paracyclophane (X in one and Y in the other aromatic ring) is one of the above groups, then the four possible isomers (not counting enantiomers) each exhibits a unique nmr aromatic proton resonance pattern. When X and Y are pseudo-gem, no signal for a proton pseudo-gem to the down-shifting group is observed. When X and Y are pseudo-meta, the proton pseudo-gem to the down-shifting group is split by its ortho and para protons, and appears as a doublet (J=8 Hz). When X and Y are pseudo-ortho, the proton pseudo-gem to the down-shifting group is split only by its meta and para protons, and appears as a broad singlet or close doublet. When X and Y are pseudo-para, the proton pseudo-gem to the down-shifting group is split by its meta and ortho protons, and appears as a doublet of doublets (J1 = 8 Hz, J2 = 2 Hz). The structures of 40 disubstituted [2.2]paracyclophanes have been assigned on this basis. A unique halogen-aromatic ring absorption has been observed in the infrared spectra of all [2.2]paracyclophanes substituted with halogen, and occurs from 1029 to 1099, depending on the nature of the halogen and other substituents. This band was useful for analysis of mixtures. The carbonyl stretching frequency of pseudo-gem-bromoacetyl[2.2]paracyclophane was found to be moved to 1663 cm-1 from 1666-1668 cm-1 for the other isomers. This frequency decrease may be due to transannular Br• • •C=O interactions. The mass spectra of the substituted [2.2]paracyclophanes at low ionizing voltages (12 eV) show predominant fragmentation to the substituted p-xylylene (or elements thereof) ion radicals. Thus, the mass spectrum provides a convenient analytical tool for the determination of the number of substituents on each aromatic ring of a polysubstituted [2.2]paracyclophane. Correlations between structures and other physical properties of disubstituted [2.2]paracyclophanes have been summarized. For example, pseudo-gem isomers tend to melt higher, to move slower on tic, and to be more insoluble than the other isomers. © 1969, American Chemical Society. All rights reserved.
