Temperature-dependent conformational energetics, interconversion kinetics and rotational spectroscopy of interstellar 2-methoxyethanol

Abstract The conformational stability, interconversion kinetics, and spectroscopic properties of 2-methoxyethanol (2-MOE; CH 3 OCH 2 CH 2 OH), a recently detected interstellar alkoxy alcohol toward the high-mass star-forming cloud NGC 6334I, have been investigated using the long-range corrected hybrid density functional ωB97XD together with high-level DLPNO-CCSD(T) calculations. Four low-lying conformers, namely tGg-MOE, gGg-MOE, tTg-MOE, and tTt-MOE, were characterized at 10, 170, and 298.15 K to simulate cold molecular clouds, warm/translucent clouds, and near-ambient conditions. The calculations identify tGg-MOE as the global minimum conformer, while gGg-MOE, tTg-MOE, and tTt-MOE lie 5.56, 11.18, and 11.28 kJ mol⁻¹ higher in energy, respectively. The gGg-MOE → tGg-MOE interconversion is strongly exothermic but kinetically suppressed at low temperature because of comparatively larger activation barriers, whereas the tTg-MOE → tTt-MOE pathway remains accessible even at 10 K owing to its shallow barrier (~1 kJ mol⁻¹). Transition State Theory calculations reveal that conformational kinetics are highly temperature dependent, with low-barrier processes dominating under cryogenic interstellar cloud conditions. Molecular electrostatic potential analysis demonstrates pronounced conformerdependent charge redistribution, with the terminal oxygen atom acting as the primary electron-rich reactive center. Rotational spectroscopic calculations reproduce available experimental constants with high accuracy and show strong conformational sensitivity, particularly in the centrifugal distortion parameters associated with torsional flexibility. The present study establishes a direct relationship between conformational energetics, low-temperature kinetics, and rotational spectroscopic observables, providing important theoretical support for future laboratory and astronomical identification of 2-methoxyethanol in chemically rich interstellar clouds.