Rich Collection of n‑Propylamine and Isopropylamine Conformers: Rotational Fingerprints and State-of-the-Art Quantum Chemical Investigation

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.研究人员通过结合高精度量子化学计算与高分辨转动光谱学的整合策略，对异丙胺（isopropylamine）和正丙胺（n-propylamine）的构象异构现象开展了系统研究。本研究采用所谓的‘廉价’复合计算方案——该方案将耦合簇方法与二阶莫勒-普莱瑟微扰理论相结合，用于外推至完全基组极限，从而计算得到了所有构象异构体的平衡结构及其对应的平衡转动常数与相对能量。此外，研究借助基于密度泛函理论的计算方法，获取光谱参数并考量振动效应的影响。在量子化学预测结果的指导下，研究团队利用傅里叶变换微波光谱仪与调频式毫米/亚毫米波段光谱仪，在2至400 GHz的频率范围内对两种目标分子的转动光谱进行了探测。光谱指认工作证实了多种稳定性相近的构象异构体的存在，并指出部分构象异构体之间可能存在科里奥利共振效应。