The Spectroscopic Consequences of C−H···π H-Bonding:  C₆H₆−(C₄H₂)_n Clusters with n = 1 and 2

Abstract

The ultraviolet and infrared spectra of the C6H6−(C4H2) n complexes with n = 1 and 2 have been formed and studied in a supersonic expansion using resonant two-photon ionization (R2PI), resonant ion-dip infrared spectroscopy (RIDIRS), and IR−UV hole-burning spectroscopy. A T-shaped structure is deduced for the complex, with the C4H2 centered, end on, over the benzene ring. This C−H···π H-bond shifts the frequency of the vibronic transitions of C6H6 by 161 cm-1 to the blue. The acetylenic CH stretch fundamental of C4H2 is localized and split by formation of the π H-bond. The H-bonded CH stretch fundamental is lowered in frequency by about 40 cm-1, increased in intensity by more than a factor of 2, and split by a Fermi resonance that is turned on by the complexation. The C6H6−(C4H2)2 complex has a structure that makes the S1−S0 origin transition weakly allowed and possesses an infrared spectrum that has acetylenic CH stretch absorptions due to free CH, aromatic π-bound CH, and a more weakly π-bound CH. Its structure is tentatively assigned as a cyclic, “pinwheel” structure.

Toward Selection of Efficient Density Functionals for van der Waals Molecular Complexes: Comparative Study of C–H···π and N–H···π Interactions

“…Infrared (IR) spectroscopy was used to characterize the C−H stretching frequency of C−H···π interactions in the complexes. 2,41,46,47,58,59 Vibrational spectroscopy is also useful in characterizing N−H···π interactions in small clusters involving pyrrole. 3 46 for the vibrational mode of interacting C−H of acetylene when it forms complex with benzene.…”

A theoretical study of methylation and CH/π interactions in DNA intercalation: methylated 1,10-phenanthroline in adenine–thymine base pairs

“…20 Ab initio calculations of the benzene clusters with small hydrocarbon molecules 8,[21][22][23] conrmed this preference and the role of weak electrostatic interactions in stabilizing this orientation. Nevertheless, while electrostatic forces play a major role in conventional hydrogen bonds, 24,25 the CH/p interaction has been mainly attributed to the dispersion forces, 8,20,[26][27][28][29][30][31][32][33][34][35][36][37] namely when aliphatic or aromatic CH groups are involved. Electrostatic contributions may become more relevant for species involving strong CH donors such as chloroform or acetylenic CH.…”

Conformational studies of benzyl alcohol and benzyl fluoride

“…T he conformational properties of benzyl compounds, C 6 H 5 CH 2 X, with flexible ligands have been the subject of several experimental and theoretical studies [1][2][3][4][5][6][7][8][9][10][11]. When X is an alkyl group, an amine or a halide, the COCOCOX dihedral angle is 90°and the COX bond lies in a plane orthogonal to the benzene ring [12][13][14][15][16][17][18][19]. This orientation is consistent with a model that minimizes steric repulsion effects between the X of the OCH 2 X group and the closest hydrogens in the phenyl ring.…”