Structural motifs of 2-(2-fluoro-phenyl)-ethylamine conformers

Abstract

a Vibronic and vibrational spectra of 2-(2-fluoro-phenyl)-ethylamine (2-FPEA) conformers were measured in a molecular beam by resonant two-photon ionization (R2PI), ultraviolet-ultraviolet hole burning (UV-UV HB) spectroscopy, and ionization-loss stimulated Raman spectroscopy (ILSRS). The measured ILSR spectral signatures in the survey spectra of the amino group region and in the broad spectral range revealed the presence of five different conformers, which were confirmed by the HB spectra. The determination of the structures of the conformers of 2-FPEA was assisted by quantum chemical calculations of the torsional potential energy surface and of the scaled harmonic Raman spectra.Comparison of the measured ILSR spectra with the calculated Raman spectra allowed us to identify one gauche structure with the ethylamino side chain folded toward the fluorine atom, two gauche structures with the ethylamino side chain folded to the opposite side and two anti conformers with extended tails.The effect of fluorination on the spectra and on the stability and structures of these species is discussed.

Effects of Aromatic Fluorine Substitution on Protonated Neurotransmitters: The Case of 2‐Phenylethylamine

“…The two lowest‐energy isomers have a folded ( gauche ) conformation of the side chain stabilized by an NH⋅⋅⋅π interaction, whereas the two highest‐energy extended ( anti ) conformers lack this stabilizing intramolecular noncovalent interaction. The substantial influence of aromatic monofluorination in ortho position on the potential energy surface of PEA, with respect to the structures and relative energies of the various conformers, has been studied using microwave, Raman, and electronic spectroscopy as well as quantum chemical calculations of o F‐PEA . The five lowest‐energy conformers of o F‐PEA (three gauche and two anti ) have been identified.…”

“…The substantial influence of aromatic monofluorination in ortho position on the potential energy surfaceo fP EA, with respect to the structures and relative energieso ft he various conformers, has been studied using microwave, Raman, and electronic spectroscopy as well as quantum chemical calculations of oF-PEA. [50,51] The five lowest-energy conformers of oF-PEA (three gauche and two anti)h ave been identified. Energetically favored are the gauche conformers in which the side chain is interacting with the aromatic ring.…”

Revealing the Structure and Noncovalent Interactions of Isolated Molecules by Laser-Desorption/Ionization-Loss Stimulated Raman Spectroscopy and Quantum Calculations

“…51 Then, this geometry is further optimized, with Gaussian 09, 52 using DFT calculations with the Becke three-parameter hybrid functional combined with the Lee−Yang−Parr correlation functional (B3LYP) 53,54 and the 6-311 ++ G(d,p) basis set to obtain the energetic, structural, vibrational, and electronic properties of TRA. The harmonic frequencies of vibrations are scaled by the previously derived factors 23 of 0.956 and 0.964 for the N−H and C−H stretches, respectively, and 0.946 for the low <1600 cm −1 frequency range. Finally, the calculated Raman spectra are obtained while accounting for the Raman activities, converted to Raman intensities, 42 and, for the scaled harmonic fundamental frequencies, convolved with pure Lorentzian lines of fwhm of 0.5 cm −1 .…”

“…Similar to IR-IDS, in ILSRS, ,− the UV laser is tuned to the transition of a specific isomer, but two different VIS beams, i.e., a fixed frequency pump (ω p ) and a tunable Stokes-shifted frequency (ω S ) are used, where ω p – ω S can match Raman transitions of the probed species. Under these conditions, depletion of a certain percent of the ground vibrational-state population occurs, leading to a loss in the ionization signal and, consequently, to isomer-specific Raman signatures.…”

Infrared spectrum of the cold ortho-fluorinated protonated neurotransmitter 2-phenylethylamine: competition between NH+⋯π and NH+⋯F interactions

“…15 The IRPD spectra of oF-H + PEA-Rg presented here allow for a clear-cut conformer assignment and provide for the first time invaluable experimental information of the drastic effects of ortho-fluorination on the NH + Á Á Áp interaction in this prototypical protonated neurotransmitter, which are much more pronounced than those deduced for neutral PEA. 31,32…”