Microwave spectroscopic and theoretical studies on the phenylacetylene⋯H2O complex: C–H⋯O and O–H⋯π hydrogen bonds as equal partners

Abstract

Rotational spectra of five isotopologues of the title complex, C(6)H(5)CCH···H(2)O, C(6)H(5)CCH···HOD, C(6)H(5)CCH···D(2)O, C(6)H(5)CCH···H(2)(18)O and C(6)H(5)CCD···H(2)O, were measured and analyzed. The parent isotopologue is an asymmetric top with κ = -0.73. The complex is effectively planar (ab inertial plane) and both 'a' and 'b' dipole transitions have been observed but no c dipole transition could be seen. All the transitions of the parent complex are split into two resulting from an internal motion interchanging the two H atoms in H(2)O. This is confirmed by the absence of such doubling for the C(6)H(5)CCH···HOD complex and a significant reduction in the splitting for the D(2)O analog. The rotational spectra, unambiguously, reveal a structure in which H(2)O has both O-H···π (π cloud of acetylene moiety) and C-H···O (ortho C-H group of phenylacetylene) interactions. This is in agreement with the structure deduced by IR-UV double resonance studies (Singh et al., J. Phys. Chem. A, 2008, 112, 3360) and also with the global minimum predicted by advanced electronic structure theory calculations (Sedlack et al., J. Phys. Chem. A, 2009, 113, 6620). Atoms in Molecule (AIM) theoretical analysis of the complex reveals the presence of both O-H···π and C-H···O hydrogen bonds. More interestingly, based on the electron densities at the bond critical points, this analysis suggests that both these interactions are equally strong. Moreover, the presence of both these interactions leads to significant deviation from linearity of both hydrogen bonds.

Microwave Spectroscopic and Atoms in Molecules Theoretical Investigations on the Ar⋅⋅⋅Propargyl Alcohol Complex: Ar⋅⋅⋅HO, Ar⋅⋅⋅π, and Ar⋅⋅⋅C Interactions

“…Splittings in a-and b-type transitions are of the order of a few kilohertz, whereas splitting in the c-type transitions is relatively larger (0.9-2.6 MHz) and decreases in the order Ar···PA > Ar···PA-D(CD) > Ar···PA-D(OD). [14] Goswami and Arunan reported the microwave spectrum of C 6 H 5 CCH···H 2 O, [15] thereby providing positive confirmation for the structure proposed by Patwari's group. Atoms in molecules (AIM) and electrostatic potential calculations are used to explore the nature of the interactions in this complex.…”

“…[13] Recently, Patwari and co-workers have investigated many complexes of phenylacetylene (C 6 H 5 CCH), another multifunctional molecule, by infrared-optical double resonance spectroscopy and showed the diversity in the complex structures. [14] Goswami and Arunan reported the microwave spectrum of C 6 H 5 CCH···H 2 O, [15] thereby providing positive confirmation for the structure proposed by Patwari's group. Although the main objective of this study was to find whether H 2 O acts as a hydrogen-bond donor to the p electrons or as an acceptor to the acetylenic H atom, the results revealed that the complex had a cyclic structure in which H 2 O played both roles.…”

Rotational spectra of propargyl alcohol dimer: A dimer bound with three different types of hydrogen bonds

“…For example, the phenylacetylene· · ·H 2 O complex is stabilized by O-H· · ·π and C-H· · ·O hydrogen bonds. 22,51 Carboxylic acids form two strong symmetric hydrogen bonds on dimer formation. 52 The PA appears to be the smallest molecule exhibiting three different hydrogen bonds on dimer formation.…”

“…Microwave (MW) spectroscopy in a molecular beam has been used for positive confirmation of the structure(s) when there is a possibility of different conformers of molecules and many different minima of weakly bound complexes. [21][22][23] Such is the case of the propargyl alcohol dimer.…”

The Unexplored World of Cycloalkene–Water Complexes: Primary and Assisting Interactions Unraveled by Experimental and Computational Spectroscopy

“…[11,12] While strong HBs are well characterized, [13] weak OÀH···p interactions are less explored. Some alkyne complexes with water [14] and alcohols [15] have indeed been studied, together with complexes of phenol with ethylene and acetylene [16] as well as of tert-butyl alcohol with bulky alkenes. [17] However,if one excludes the molecular complexes involving aromatic systems as the p-partner in the interaction, [18][19][20][21] olefinic···HÀ Oc ontacts remain surprisingly unexplored, with ethylenewater and ethylene-methanol being, to the best of our knowledge,t he only clusters well characterized.…”