Microwave Spectra, Structure, and the Aromatic Character of 1-Chloroborepin

Area of Science:

• Chemical Physics
• Molecular Spectroscopy
• Quantum Chemistry

Background:

• 1-chloroborepin is a somewhat unstable organoboron compound.
• Understanding the structure and bonding of novel boron-containing heterocycles is crucial for materials science and synthetic chemistry.

Purpose of the Study:

• To determine the high-resolution molecular parameters of 1-chloroborepin.
• To investigate the electronic structure and bonding characteristics of 1-chloroborepin.
• To confirm the aromaticity of this boron-containing molecule.

Main Methods:

• High-resolution pulsed beam Fourier transform microwave spectroscopy was employed.
• Microwave spectra were measured for three isotopologues: 11B35Cl, 10B35Cl, and 11B37Cl.
• An extended Townes-Dailey analysis was performed using experimental quadrupole coupling strengths.

Main Results:

• Rotational constants and molecular parameters were determined for the 11B35Cl isotopologue.
• An inertial defect of -0.174 amu Ų indicated a planar structure with out-of-plane vibrational motion.
• Analysis revealed electron density sharing between chlorine and the boron p-orbital, with a B-Cl bond length of 1.798(1) Å.

Conclusions:

• The structural and electronic properties of 1-chloroborepin are consistent with an aromatic boron-containing molecule.
• The study provides detailed insights into the bonding and electronic configuration of this unique heterocycle.
• Experimental data supports the aromatic nature and planar geometry of 1-chloroborepin.