Magnitude and Nature of Interactions in Benzene−X (X = Ethylene and Acetylene) in the Gas Phase:  Significantly Different CH/π Interaction of Acetylene As Compared with Those of Ethylene and Methane

Abstract

The accurate interaction energies of the CH/pi interaction in the benzene-X clusters (X = ethylene and acetylene) were experimentally and theoretically determined. Two-color multiphoton ionization spectroscopy was applied, and the binding energies in the neutral ground state of the clusters were evaluated from the dissociation threshold measurements of the cluster cations. The experimental binding energies of the clusters (D0) were 1.4+/-0.2 and 2.7+/-0.2 kcal/mol, respectively. Estimated CCSD(T) interaction energies for the clusters at the basis set limit (De) were 2.2 and 2.8 kcal/mol, respectively. Calculated D0 values (1.7 and 2.4 kcal/mol, respectively) are close to the experimental values. Large electron correlation contributions (Ecorr=-3.6 and -2.8 kcal/mol, respectively) show that dispersion is the major source of the attraction in both clusters. The electrostatic interaction in the ethylene cluster is very small (-0.38 kcal/mol), as in the case of the benzene-methane cluster, whereas the electrostatic interaction in the acetylene cluster is large (-1.70 kcal/mol). The shifts of the S1-S0 transition also suggest that the ethylene cluster is a van der Waals-type cluster, but the acetylene cluster is a pi-hydrogen-bonded cluster. The nature of the CH/pi interaction of the "activated" alkyne C-H bond is significantly different from that of the "nonactivated" (or typical) alkane and alkene C-H bonds.

Properties of the Solute-Stationary Liquid Interactions in Gas Liquid Chromatography

“…5,6) However, typical CH/p complexes such as benzene-methane [7][8][9] have been shown primarily of dispersion interactions based on high-level ab initio calculations. The interaction energies were also consistent with the experimental binding energy D o of benzene-X (Xϭmethane, 10) ethylene and acetylene, 26) and benzene 27,28) ) as CH/p complexes and benzene-XH 2 (XϭN 29) and O [30][31][32] ) as the T-shape form of hydrogen bonds. Both the calculated and experimental binding energies in the weak interaction showed a linear correlation, as shown in Fig.…”

Accurate dissociation energies of two isomers of the 1-naphthol⋅cyclopropane complex

“…9 Larger CH · · · π complexes, such as benzene·alkanes, were measured using a two-color appearance potential method. 20,21 Again a linear correlation with the average molecular polarizabilities was found. 6,7 Currently, we are extending measurement of D 0 (S 0 ) values to more complex and chemically relevant cases such as 1-naphthol (1-NpOH) with hydrocarbons.…”

Isomerenselektive IR‐Spektroskopie von Benzol‐Acetylen‐Clustern: Vergleich mit der Struktur des Benzol‐Acetylen‐Cokristalls

“…Mithilfe der resonanten Zweiphotonenionisationsspektroskopie (R2PI) [7,8,12,13] [14] bei 38 606 cm À1 nachgewiesen werden. Die Blauverschiebung in den UV-Spektren deutet auf eine verminderte Clusterstabilität im elektronisch angeregten Zustand hin, die durch eine aus der pp*-Anregung resultierende, niedrigere Elektronendichte im Benzolring zustandekommt, wie es bei anderen Clustern mit Wasserstoffbrücken zum aromatischen p-System beobachtet wurde.…”