Abstract
The conformational isomerism of isopropylamine and n-propylamine has been investigated by means of an integrated strategy combining high-level quantum-chemical calculations and high-resolution rotational spectroscopy. The equilibrium structures (and thus equilibrium rotational constants) as well as relative energies of all conformers have been computed using the so-called “cheap” composite scheme, which combines the coupled-cluster methodology with second-order Møller–Plesset perturbation theory for extrapolation to the complete basis set. Methods rooted in the density functional theory have been instead employed for computing spectroscopic parameters and for accounting for vibrational effects. Guided by quantum-chemical predictions, the rotational spectra of isopropylamine and n-propylamine have been investigated between 2 and 400 GHz with Fourier transform microwave and frequency-modulation millimeter/submillimeter spectrometers. Spectral assignments confirmed the presence of several conformers with comparable stability and pointed out possible Coriolis resonance effects between some of them.
Highlights
Amines are widespread in nature and represent an important family of compounds involved in numerous natural and artificial mechanisms
More complex amines can be regarded as precursors of other proteinogenic amino acids
The signal was detected by a Schottky barrier diode and demodulated by a Lock-in amplifier set at twice the modulation frequency (2f) so that the second where / (A) contains the rotational constants in the Watson Areduced form,[41] the /cd part accounts for the centrifugal distortion terms, and /hfs is the hyperfine-structure Hamiltonian due to the presence of nitrogen, whose nuclear spin is IN = 1
Summary
Amines are widespread in nature and represent an important family of compounds involved in numerous natural and artificial mechanisms. The member when increasing the alkyl chain length, has not conclusively been detected.[10] Notwithstanding, even if a molecule is not identified, it is important to derive astronomical upper limits for its abundance to be compared with those of related species[11,12] or within astrochemical models. In this context, laboratory studies and analyses of the rotational spectra of Received: December 20, 2019 Revised: January 24, 2020 Published: January 27, 2020
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