Conformational Analysis of the Molecular Complexes of Sodium with Methanol and 1,2-Ethanediol:  Photoionization and ab Initio Molecular Orbital Studies

Abstract

The molecular complexes of the sodium atoms with methanol and 1,2-ethanediol were generated in a flow reactor and studied with photoionization mass spectrometry. The photoionization efficiency spectra of these complexes were measured and the ionization threshold energies were determined by the method of the Watanabe plots. The conformation-dependent bond dissociation energies and ionization energies of these complexes were also calculated by ab initio molecular orbital methods. The photoionization threshold energies of the sodium/methanol complex was determined to be 4.30 ( 0.02 eV, a value in good agreement with the ab initio prediction. Guided by the theoretical results, the experimental photoionization threshold energy of the cyclic conformers of the sodium/1,2-ethanediol complex was determined to be 3.95 ( 0.02 eV and that of the conformers with the concerted intramolecular H-bond was determined to be 4.32 ( 0.01 eV. The bond dissociation energy of the sodium/methanol complex was determined to be 0.28 eV. The interplay of the sodium complexation bonding and the intramolecular hydrogen bonding and its effects on both the bonding energies and the ionization energies of the conformers were discussed. The conformation-dependent physical properties of the corresponding cationic states of these complexes were also reported. Comparisons of the physical and chemical properties among the sodium/1,2-ethanediol, sodium/1,2-dimethoxyethane, and potassium/1,2-ethanediol complexes were emphasized in this study.

An Experimental and Ab Initio Study of the Nature of the Binding in Gas-Phase Complexes of Sodium Ions

“…Optimized structures for 1,2-ethanediol (1 and 2) and the most stable of its possible sodium complexes are shown in Figure 7. As shown by Yeh and Su [17] other, less stable, monodentate structures are possible. Ab initio calculations reveal the complex interplay of enthalpic and entropic factors.…”

“…Ab initio calculations on 1,2-ethanediol and its sodium complex have recently been reported by Yeh and Su. [17] Using a comparable type of wavefunction, they obtained a D 0 value of 39.7 kcal mol À1 . This is slightly larger than the present value, probably because no BSSE correction was applied.…”

Molecular Complexes between Sodium and Carbonyl Compounds: Photoionization and ab Initio Molecular Orbital Studies

“…14,15,17,19 The present spectra seem to suggest that some additional ionization channels are contributing to the ionization signal around and beyond the threshold region. One plausible source could be the autoionization process originating from the π* r n electronic transition of acetone.…”

“…The general experiment setup has been described in previous publications. 14,15,17,19 Here, only an outline of the experimental procedure which is relevant to the present carbonyl systems is given.…”

“…In this report, three main issues concerning the sodium/carbonyl systems were addressed. First, it has been well established that the natures of the bonding between the alkali metal atoms and the simple Lewis base molecules containing the hydroxyl, amino, and/or ethereal groups all belong to the same category. − For the sodium/carbonyl systems, one would like to know whether the presence of the π and π* orbitals of the carbonyl group modifies the bonding nature of the cp state. Second, the global electronic ground state consists of two general potential regions.…”