Protonated ethanol and its neutral counterparts

Area of Science:

• Physical Chemistry
• Chemical Physics
• Ion Chemistry

Background:

• Protonation of neutral molecules can lead to various isomeric ion structures.
• Understanding ion structures is crucial for interpreting mass spectrometry data and reaction mechanisms.

Purpose of the Study:

• To investigate the distinct isomers formed upon protonation of ethanol.
• To elucidate the structural differences between ethanol ions and their neutral counterparts.
• To explore the influence of ion internal energy and isotopic substitution on ion stability.

Main Methods:

• Collisionally activated dissociation (CAD) experiments.
• Neutralization-reionization (NR) experiments.
• Analysis of isotopic effects in ethanol ions.

Main Results:

• Protonation of ethanol yields two isomers: the classical ion (CH3CH2OH2+) and a proton-bound complex (C2H4…H+…OH2).
• The neutral form of the proton-bound complex is unstable, while the classical ion's neutral form can be stabilized.
• Substantial geometric differences exist between CH3CH2OH2+ and the hypervalent CH3CH2OH2·.
• Specific isotopic substitutions (e.g., C2H5OD2·) show enhanced stability compared to others (e.g., C2D5OD2·).

Conclusions:

• Ethanol protonation leads to structurally distinct ions with differing stabilities.
• Ion internal energy and isotopic labeling significantly influence the observed stability.
• The findings provide insights into ion structures and reactivity, partially explaining observed isotope effects.