(Received: September 21, 1998 ; Accepted for publication: January 18, 1999 ; Published on Web: May 19, 1999)
Enthalpies of benzene-monosubstituted benzene interactions were evaluated by semi-empirical MO calculations of heats of formation for (i) the benzene (PhH) dimer and (ii) benzene-monosubstituted benzene (PhX) pairs. Calculation methods, initial intermolecular distances (rI), and so on were investigated for the benzene dimer. The interaction enthalpy and optimized geometry calculated with PM3 were consistent with the previous experimental and theoretical results. As initial arrangements of PhH-PhX systems, one parallel (P) and four vertical arrangements (Vr , Vp , Vm , and Vb) were chosen (Figure 1). In the case of Vp or Vm arrangement where the lowest H atom at the para or meta position to substituent X in PhX was located above the centroid of PhH, calculated enthalpies of the interactions (DDHf) between PhH and PhX had close correlation with experimental ones (DDHt) determined by gas-liquid partition chromatography (GLPC), with the correlation coefficient (r) as large as 0.94 (Figure 5); differences between the experimental DDHt values and the DDHt values calculated from the correlation equation were less than ca. 0.1 kcal mol-1 . With the other arrangements except for Vp, no appreciable relationship was observed between the DDHf and DDHt (Figures 2, 3, and 4).
Keywords: Intermolecular interaction, Aromatic-aromatic interaction, Benzene-monosubstituted benzene, MOPAC93, Relationship between calculated and experimental interaction enthalpies
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