Isomerism of the Aniline Trimer

Area of Science:

• Physical Chemistry
• Molecular Spectroscopy
• Computational Chemistry

Background:

• Intermolecular forces govern molecular aggregation.
• Aniline clusters offer a model system for studying weak interactions like N-H···N, N-H···π, and C-H···π.
• Phenol trimers, with stronger hydrogen bonds, exhibit fewer aggregation isomers.

Purpose of the Study:

• To investigate the aggregation behavior of aniline trimers and monohydrated aniline dimers.
• To characterize the isomers and intermolecular interactions present in these clusters.
• To evaluate the performance of computational methods in predicting these structures.

Main Methods:

• Aniline clusters were generated using jet-cooled expansion.
• Broadband (chirped-pulsed) microwave spectroscopy was employed for probing.
• Rotational spectra were analyzed to detect and characterize isomers.

Main Results:

• Three isomers of the aniline trimer and two isomers of the monohydrated aniline dimer were identified.
• Aniline trimers exhibit diverse aggregation structures stabilized by weak N-H···N, N-H···π, and C-H···π interactions.
• Water acts as a hydrogen-bond pivot in the hydrated dimer via O-H···N interactions.

Conclusions:

• Weaker intermolecular forces in aniline systems lead to a greater variety of aggregation isomers compared to phenol.
• Computational methods like B3LYP-D3(BJ) and M06-2X show deficiencies in accurately reproducing experimental rotational data for these systems.
• The study highlights the complexity of weak interactions in molecular aggregation and the need for improved computational models.