Molecular biphenyl

Hummel and Luthjens [398] formed electron—cation pairs in cyclohexane by pulse radiolysis. With biphenyl added to the solvent, biphenyl cations and anions were formed rapidly on radiolysis as deduced from the optical spectra of the solutions. The optical absorption of these species decreased approximately as t 1/2 during the 500 ns or so after an 11ns pulse of electrons. The much lower mobility of the molecular biphenyl anion (or cation) than the solvated electron, es, (solvent or cation) increases the timescale over which ion recombination occurs. Reaction of the solvated electron with biphenyl (present in a large excess over the ions) produces a biphenyl anion near to the site of the solvated electron localisation. The biphenyl anion can recombine with the solvent cation or a biphenyl cation. From the relative rates of ion-pair reactions (electron-cation, electron—biphenyl cation, cation—biphenyl anion etc.), Hummel and Luthjens deduced that the cation (or hole) in cyclohexane was more mobile than the solvated electron (cf. Sect. 2.2 [352, 353]). 

Treatment of biphenyl (see Section 11 7 to remind yourself of its structure) with a mixture of nitric acid and sulfuric acid gave two principal products both having the molecular formula C12H9NO2 What are these two products ... 

Fig. 3a. Molecular structures of selected liole-transport molecules. Biphenyls (7a) (R = H)...

The backbone of poly(phenylene oxide)s is cleaved under certain extreme reaction conditions. Lithium biphenyl reduces DMPPO to low molecular weight products in the dimer and trimer molecular weight range (20) and converts poly(2,6-diphenyl-l,4-phenylene oxide) to 3,5-diphenylphenol in 85% yield (21) (eq. 4). 

Mesogenic diols, such as 4,4 -bis( CO-hydtoxyaLkoxy)biphenyls, ate used with 2,4-TDI or 1,4-diisocyanatobenzene (PPDI) to constmct Hquid crystalline polyurethanes (7). Partial replacement of the mesogenic diols by PTMG shows that the use of lower molecular weight flexible spacers form polymers that have a more stable mesophase and exhibit higher crystallinity (8). Another approach to Hquid crystal polyurethanes involves the attachment of cholesterol to the polyurethane chain utilizing the dual reactivity in 2,4-TDI (9). 

R. Docherty, K. J. Roberts. Modeling the morphology of molecular crystals Applications to anthracene, biphenyl and B-succinic acid. J Cryst Growth 55 159, 1988. 

Not all of these isomers are completely separated by the conditions given here, but all arc readily detected by plotting the masses of the molecular ions. Pesticides can interfere with polychlorinated biphenyl (PCB) analysis. 

In Figure 13.2, the intensity of the ion at m/z 170 represents a molecular ion of an aromatic compound. The characteristic losses from the molecular ion (M - 1, M - 28, and M - 29) suggest an aromatic aldehyde, phenol, or aryl ether. The molecular formula of Ci2H 0O is suggested by the molecular ion at m/z 170, which can be either a biphenyl ether or a phenylphenol. The simplest test to confirm the structure is to prepare a TMS derivative, even though m/z 11 strongly indicates the diaryl ether. 

More than 90 years ago Bamberger (1897) discovered that iV-nitrosoacetanilide decomposes easily in benzene to give biphenyl, acetic acid, and molecular nitrogen (Scheme 2-24). 

An investigation of the relative rates of bromination of benzene, toluene, m-and p-xylene by bromine in acetic acid, catalysed by mercuric acetate, revealed relative rates almost identical with those obtained with molecular bromine322, though as in the bromination of biphenyl by bromine acetate (p. 129) it is quite inconsistent for a much more reactive electrophile to have the same selectivity. Relative rates were (molecular bromination values in parenthesis) benzene 1.0 toluene, 480 (610) p-xylene, 2.1 x 103 (2.2 x 103) m-xylene 2.0 x 10s (2.1 x 10s). 

In some molecules the molecular dipole is simply dominated by a single polar bond. In sufficiently complex molecules there may be several polar bonds of differing strength. In this case the molecular dipole is determined by their relative orientation. Ab initio studies of 2-2 -difluoro biphenyl have revealed a strong shape dependence of the molecular dipole as a function of inter-ring angle. This is illustrated in Fig. 12. 

Fig. 12. Torsional potential and molecular dipole for 22-difluoro biphenyl...

In this section, we will describe the crystal structures of the mesogenic A -n-alkoxy-4-cyano-biphenyls (Fig. 1) [53-57]. The compounds have the phase sequences crystal-nematic-isotropic for CB05—CB07 and monotropic nematic for CB01-CB04 crystal-smectic A-nematic-isotropic for CB08. The crystal and molecular data of the investigated compounds CBOn are summarised in Table 2. 

Stacked together along the a-axis. The long molecular axes are tilted by 13° within the layers. By Raman spectral measurements Tashiro et al. found that the biphenyl group of the compound has a twisted structure in the liquid crystalline state as well as in the a-form. 

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