On the Notion of Pressure in a Canonical Ensemble

and biphenyl to 1700A,8 it is assumed that the introduction of a methylene bridge (fluorene is 2,2'-methylene-biphenyl) results in an approximately planar structure in which the phenyl groups are not symmetrical about an axis through the 4,4'-positions. This is in agreement with dipole moment measurements which favor this configuration.9 The band positions change due to alkyl substitution (bathochromic shift) and the intensities of the IBb bands decrease as is indicated by the decrease in i-values. It is to be noted that essentially the same occurs in the comparison of the spectra and the i-values of anthracene and phenanthrene. Similar regularities (bathochromic shifts and decrease in i-values) are also observed in the spectra of 2-phenylnaphthalene and its methylene derivative, 1,2-benzfluorene, and in 2-phenylazulene and its methylene derivative, indeno-azulene, as can be seen from the data in Fig. 3 and Table II, although in these