Conformations and CH/π interactions in aliphatic alkynes and alkenes

Cyclobenzoin Esters as Hosts for Thin Guests

Cyclotetrabenzoin esters can host terminal triple bonds of alkynes and nitriles in their cavities, as revealed by cocrystal structures of four such complexes. Within cyclotetrabenzoin cavities, π-clouds of triple bonds establish favorable and virtually equidistant interactions with the four aromatic walls of the cyclotetrabenzoin skeleton. Binding is selective for aliphatic nitriles and terminal alkynes, with their aromatic counterparts residing outside of the cyclotetrabenzoin cavity.

Experimental and Theoretical Soft X-ray Study of Nicotine and Related Compounds

The valence and core electronic structure of nicotine, nicotinic acid, and nicotinamide have been studied by photoelectron and soft X-ray absorption spectroscopy, supported by theoretical calculations, which take into account conformational isomerism. The core-level photoionization spectra of all molecules have been assigned, and theory indicates that the effects of conformational differences are small, generally less than the natural line widths of the core ionic states. However, in the case of nicotinamide, the theoretical valence ionization potentials of cis and trans conformers differ significantly in the outer valence space, and the experimental spectrum is in agreement with the calculated outer valence cis conformer spectrum. In addition, the C, N, and O K edge near-edge absorption fine structure spectra are reported and interpreted by comparison with reference compounds. We find evidence at the N and O K edges of interaction between the delocalized orbitals of the pyridine ring and the substituents for nicotinic acid and nicotinamide. The strength of the interaction varies because the first is planar, while the second is twisted, reducing the extent of orbital mixing.

Deeper Insights into Conformational Analysis of cis-Butene and 1-Alkenes as Monomers and Dimers: QTAIM, NCI, and DFT Approach

A few theoretical and experimental studies have been done so far about the properties and the conformational analysis of alkenes as monomers and dimers. Deeper insights into the conformational analysis of monomers and dimers of alkenes and the relation with boiling point are done in this work. In low-lying cis-butene, there is no repulsive interaction between methyl groups but there is an attractive hydrogen-hydrogen bonding. In monomers of 1-alkenes, the most stable conformer has bent-inward geometry which favors the π bond interaction with methyl/methylene hydrogen/carbon atoms. Conversely, each alkene’s molecule in the corresponding most stable alkene’s dimer has a straight, zig-zag geometry. Two straight, zig-zag alkene’s molecules in the corresponding most stable dimer have only one type of intermolecular interaction (hydrogen-hydrogen bonding). As a consequence, very good linear relationships between a physical property (such as boiling point) and theoretical parameters are obtained.

Electronic Properties of Chlorine, Methyl, and Chloromethyl as Substituents to the Ethylene Group--Viewed from the Core of Carbon

"Substituent effects" is an important and useful concept in organic chemistry. Although there are many approaches to parametrizing the electronic and steric effects of substituents, the physical basis for the parameters is often unclear. The purpose of the present work is to explore the properties of chemical shifts in carbon 1s energies as a well-defined basis for characterizing substituents to an ethylene C═C moiety. To this end, high-resolution carbon 1s photoelectron spectra of six chloro-substituted ethenes and seven chloro-substituted propenes have been measured in the gas phase. Site-specific adiabatic ionization energies have been determined from the spectra using theoretical ab initio calculations to predict the vibrational structures. For two molecules, 3-chloropropene and 2,3-dichloropropene, the spectral analyses give quantitative results for the conformer populations. The observed shifts have been analyzed in terms of initial-state (potential) and relaxation effects, and charge relaxation has also been analyzed by means of natural resonance theory. On the basis of core-level spectroscopy and models, chlorine, methyl, and chloromethyl have been characterized in terms of their effect on the carbon to which they are attached (α site) as well as the neighboring sp(2) carbon (β site). The derived spectroscopic substituent parameters are characterized by both inductive (electronegativity) effects and the ability of each substituent to engage in electron delocalization via the π system. Moreover, the adopted approach is extended to include substituent-substituent interaction parameters.