Using He droplets for measurements of interconversion enthalpy of conformers in 2-chloroethanol

Abstract

2-chloroethanol molecules having temperature from 300 to 600 K have been captured by helium droplets and the infrared spectra of the O–H and C–H stretching bands of the embedded molecules have been obtained. The intensity ratio of the bands due to trans and gauche conformers of the molecules follows the Arrhenius dependence, giving the enthalpy of conformers interconversion of 1.1 kcal/mol. It is concluded that the abundance ratio of the conformers, which are at equilibrium in the gas phase, remains unchanged upon the rapid cooling of the molecules in the helium droplets.

Infrared laser spectroscopy of the helium-solvated allyl and allyl peroxy radicals

“…Of course, in the limit of slow vibrational cooling, the system would "anneal" to the global minimum, and only the lowest energy conformer would be present at equilibrium in the 0.4 K droplet ensemble. However, the rate of energy dissipation via He atom evaporation has been shown to be sufficiently rapid to kinetically trap non-global minimum conformations of many other species, such as 2-chloroethanol, 42 tryptophan, 43 and tyrosine. 43 In these cases, the intact gas-phase molecules were picked-up by the droplets, and the equilibrium conformer distribution at the vapor temperature was largely preserved upon cooling to 0.4 K. 44,45 Moreover, as molecular cluster systems condense within He droplets, metastable structures are often kinetically trapped behind small isomerization barriers (greater than about 100 cm −1 ), 39,40,[46][47][48] although there are notable exceptions.…”

Ab initioStudy of Hyperconjugative Effect on Electronic Wavefunctions of 2-chloroethanol

“…These experimental findings were confirmed by ab initio calculations [4, 10−12] at different levels of theory ranging from Hartree-Fock (HF) up to the second-order Møller-Plesset perturbation theory (MP2) and the coupled cluster singles and doubles (CCSD) level of theory. Most theoretical studies have focused on the stability and structural parameters of 2-chloroethanol conformers [4,10,11], comparison of experimental and calculated the gas-phase vibrational spectra of 2chloroethanol [4,7], calculation of barriers to internal rotation between different conformers [7]. However, the analysis of hyperconjugative effects on the stability and electronic wavefunctions of 2-chloroethanol conformers has not been reported so far.…”

Communication: Helium nanodroplet isolation and rovibrational spectroscopy of hydroxymethylene

“…In a similar fashion, we estimate a ratio of 1:2.4. A combination of the rapid cooling inherent to He droplets, [34][35][36] and the millisecond timescale of the experiment could indeed yield the larger ratio of HCOH to FA observed in the He droplet experiment. The survey scan ( Figure S1 of the supplementary material 22 ) did not reveal any lines that could be assigned to the cis-conformation of hydroxymethylene (cHCOH), although the VCI computations 19 predict the ν 3 + ν 5 combination band to be the only transition with significant intensity (>10 km/mol) in the surveyed region.…”