Evidence for a C–H⋯π type weak interaction: 1 : 1 complex of styrene with acetylene studied by mass selective high-resolution UV spectroscopy and ab initio calculations

Synthesis of Azacalixarenes and Development of Their Properties

This review focuses on the synthesis, structure, and interactions of metal ions, the detection of some weak interactions using the structure, and the construction of supramolecules of azacalixarenes that have been reported to date. Azacalixarenes are characterized by the presence of shallow or deep cavities, the simultaneous presence of a basic nitrogen atom and an acidic phenolic hydroxyl group, and the ability to introduce various side chains into the cyclic skeleton. These molecules can be given many functions by substituting groups on the benzene ring, modifying phenolic hydroxyl groups, and converting side chains. The author discusses the evidence of azacalixarene utilizing these characteristics.

Benzene⋯acetylene: a structural investigation of the prototypical CH⋯π interaction

The benzene⋯acetylene dimer is a symmetric top with μ = 0.438(11) D and H⋯π = 2.4921(1) Å.

The CH/π hydrogen bond in chemistry. Conformation, supramolecules, optical resolution and interactions involving carbohydrates

The CH/π hydrogen bond is an attractive molecular force occurring between a soft acid and a soft base. Contribution from the dispersion energy is important in typical cases where aliphatic or aromatic CH groups are involved. Coulombic energy is of minor importance as compared to the other weak hydrogen bonds. The hydrogen bond nature of this force, however, has been confirmed by AIM analyses. The dual characteristic of the CH/π hydrogen bond is the basis for ubiquitous existence of this force in various fields of chemistry. A salient feature is that the CH/π hydrogen bond works cooperatively. Another significant point is that it works in nonpolar as well as polar, protic solvents such as water. The interaction energy depends on the nature of the molecular fragments, CH as well as π-groups: the stronger the proton donating ability of the CH group, the larger the stabilizing effect. This Perspective focuses on the consequence of this molecular force in the conformation of organic compounds and supramolecular chemistry. Implication of the CH/π hydrogen bond extends to the specificity of molecular recognition or selectivity in organic reactions, polymer science, surface phenomena and interactions involving proteins. Many problems, unsettled to date, will become clearer in the light of the CH/π paradigm.

High resolution IR spectroscopy of acetylene-furan in ultracold helium nanodroplets

We have measured the IR spectrum of the acetylene-furan complex in ultracold helium nanodroplets in the region of the nu(3) CH(asym)-stretch vibration of the acetylene (between 3240 and 3300 cm(-1)). We have observed eight bands that can be attributed to acetylene-furan complexes. Two of these bands are assigned to two different isomers of the 1:1 acetylene-furan complex. The vibrational band at 3267.4 cm(-1) is assigned to the CH(asym)-stretch vibration of the dimer structure with the C-H of the acetylene being attached to the pi-system of the furan. The peak at 3272.1 cm(-1) is assigned to the CH(asym)-stretch vibration of the dimer structure with the C-H of the acetylene being attached to the oxygen atom of the furan. These assignments are confirmed by additional measurements of the spectrum of the (13)C-acetylene-furan complex.

Van der Waals Bonding to a Molecule with π-Electron Conjugation: Styrene-Argon Complex Studied by Mass Selective High Resolution R2PI UV Spectroscopy and Ab-initio Calculations

Combining high-resolution mass-selective resonance-enhanced two-photon ionization spectroscopy analysed by genetic-algorithm-based computer-assisted rotational fit and high-level ab initio calculations we were able to determine the structure and the transition moment orientation of the styrene-Ar complex. The results demonstrate that Ar binds to the benzene ring of styrene. The binding site of Ar is 3.42 Å above the benzene-ring plane and is close to the C 6 symmetry axis of the aromatic ring, but slightly shifted to the vinyl group, which implies that the binding pattern is perturbed by the presence of the bonded to the benzene ring vinyl group. The transition moment ratio of the styrene-Ar complex is considerably different from the one of bare styrene this being a purely mass effect stemming from the reorientation of the principal axes of inertia upon the cluster formation. The red shift of the 00 0 origin band of the styrene-Ar2 complex is almost twice that of the single complex, indicating that the red-shift additivity rule holds in this case. On this basis we conclude that the second Ar atom is bound to the opposite side of the benzene ring.