Tuning halogen bond donor ability: benchmarking substituent effects in fluoroiodobenzenes

Area of Science:

• Molecular spectroscopy
• Quantum chemistry
• Chemical bonding

Background:

• Electric nuclear quadrupole coupling provides insights into molecular electronic structure.
• Fluorine substituents exert significant electronic effects (mesomeric and inductive) in aromatic systems.
• Understanding halogen bond donor abilities is crucial in supramolecular chemistry.

Purpose of the Study:

• To systematically investigate the mesomeric and inductive effects of fluorine substituents in fluoroiodobenzenes.
• To quantify iodine atom polarization and its halogen bond donor ability using the iodine atom as a probe.
• To benchmark theoretical methods for predicting molecular structures and nuclear quadrupole coupling constants.

Main Methods:

• Cavity resonator Fourier transform microwave jet spectroscopy for characterizing 19 fluoroiodobenzene substitution patterns.
• Extended Townes-Dailey model for quantifying iodine atom polarization.
• Intrinsic basis bonding analysis (IBBA) for comparison.
• Vibrational perturbation theory of second order (VPT2) to assess zero-point effects on rotational constants.

Main Results:

• Measured nuclear quadrupole coupling constants for all 19 fluoroiodobenzene isomers.
• Quantified iodine atom polarization, revealing the influence of fluorine substituents on halogen bond donor ability.
• Validated theoretical methods against extensive experimental data for structure and coupling constant predictions.

Conclusions:

• Mesomeric and inductive effects of fluorine substituents significantly modulate the electronic structure and halogen bonding capabilities of iodine in fluoroiodobenzenes.
• The study provides a rigorous benchmark for computational chemistry methods in predicting spectroscopic properties.
• Detailed understanding of substituent effects on halogen bond donation is established.