Heats of Sublimation of Polycyclic Aromatic Hydrocarbons and Their Molecular Packings

Abstract

Abstract The vapour pressure of some polycyclic aromatic hydrocarbons was measured by means of the effusion method. From the temperature dependence of the pressure, the heat of sublimation (ΔH kcal/mol) and the entropy (ΔS° cal/mol·deg) were calculated for the following hydrocarbons: 1,2-benzanthracene (ΔH=22.8; ΔS°=44.8), tetracene (29.8; 43.3), chrysene (28.1; 43.0), triphenylene (25.6; 33.9), 3,4-benzophenanthrene (25.4; –) p-terphenyl (28.3; 47.9), 1,12-benzperylene (30.0; 40.7), 3,4-benztetraphene (32.6; 45.9), 1,2,5,6-dibenzanthracene (33.9; 49.3), pentacene (37.7; 48.9), picene (33.5; 45.9), coronene (30.7; 36.9), 1,2,4,5-dibenzpyrene (32.9; 48.3), 1,2,6,7-dibenzpyrene (35.1; 45.6), 1,3,5-triphenylbenzene (34.0; 55.6), tetrabenzonaphthalene (33.9; 47.4), isoviolanthrene A (52.2; 54.6), violanthrene A (46.8; 48.1), violanthrene B (36.7; 38.0) and tetrabenzoperylene (28.2; 44.7). The small values of ΔH for violanthrene B, tetrabenzoperylene and tetrabenzonaphthalene may reflect the existence of the non-coplanar structure of their molecules. Further, the large values of ΔS° for triphenylbenzene and terphenyl suggested the possibility of the rotation about their single bonds.