Quantum-chemistry-aided identification, synthesis and experimental validation of model systems for conformationally controlled reaction studies: separation of the conformers of 2,3-dibromobuta-1,3-diene in the gas phase

Abstract

The successful separation of the gauche and s-trans conformers of 2,3-dibromobutadiene paves the way for studies of conformer-selected polar cycloaddition reactions in a cold and controlled environment.

Conformer-specific polar cycloaddition of dibromobutadiene with trapped propene ions

“…A molecular beam of the rotationally and vibrationally cold neutral diene DBB in neon carrier gas was prepared by a pulsed supersonic expansion, see Methods and ref. 36 . The collimated beam passed through an electrostatic deflector in which a strong electric-field gradient induced a spatially varying Stark-energy shift for polar molecules 24 , 36 .…”

“… 36 . The collimated beam passed through an electrostatic deflector in which a strong electric-field gradient induced a spatially varying Stark-energy shift for polar molecules 24 , 36 . This resulted in a force acting on the polar gauche -DBB (dipole moment μ gauche = 2.3 D 36 ), which was thus vertically deflected from the beam axis in contrast to the apolar s-trans conformer ( μ trans = 0 D).…”

“…Directing such a controlled molecular beam at a reaction target of trapped ions has enabled kinetic and mechanistic studies of individual conformers of 3-aminophenol with Ca + ions 33 , 34 as well as nuclear-spin-selected water molecules with diazenylium ions (N 2 H + ) 35 . In a recent study, we reported the successful electrostatic separation of the conformers of 2,3-dibromobuta-1,3-diene in a molecular beam 36 . DBB exists in an apolar s-trans and a polar gauche conformation (the s-cis conformation constitutes a saddle point on the potential-energy surface (PES) of this molecule).…”

A novel crossed-molecular-beam experiment for investigating reactions of state- and conformationally selected strong-field-seeking molecules

“…For the analysis of the experimental results, trajectories of molecules travelling from the source through the electrostatic deflector up to the reaction region were simulated using a Monte-Carlo approach implemented in home-written code. 59,65,69,70,79 Briefly, the Stark energy of the individual rotational states of the molecules in a specific external electric field was computed using the CMI Stark software package. 80 The electrostatic field of the deflector was calculated using COMSOL Multiphysics.…”

“…[51][52][53][54] Moreover, laser-based optical techniques were applied for the deflection and deceleration of neutral, strong-field-seeking molecules. [55][56][57][58] Furthermore, arXiv:2105.06427v1 [physics.chem-ph] 13 May 2021 electrostatic deflection of strong-field-seeking molecules in inhomogeneous electric fields 59 enabled not only the selection of individual rotational states in small systems, [60][61][62] but also the spatial separation of individual conformers of more complex species like different aromatic compounds, 49,63,64 2,3-dibromobuta-1,3-diene, 65 methyl vinyl ketone 66 and dipeptides. 67 Recently, we successfully applied this method in our laboratory 68 to the study of reactive collisions of conformationally selected 3-aminophenol molecules with trapped Ca + ions 69,70 and different nuclear-spin isomers of water with N 2 H + ions.…”