Neutral homoaromaticity in some heterocyclic systems

Area of Science:

• Organic Chemistry
• Computational Chemistry
• Quantum Chemistry

Background:

• Homoaromaticity is a key concept in understanding aromaticity in non-classical systems.
• Bicyclo[3.2.1]octane scaffolds offer a unique framework for investigating electronic properties.
• Heteroatom substitution provides a versatile route to tune electronic characteristics.

Purpose of the Study:

• To evaluate neutral homoaromaticity in modified bicyclo[3.2.1]octane systems.
• To investigate the impact of various heteroatom substitutions (BH, AlH, Be, Mg, O, S, PH, NH) on electronic properties.
• To classify the degree of homoaromaticity in the studied heterocyclic systems.

Main Methods:

• Density Functional Theory (DFT) calculations were employed.
• Homodesmotic equations were utilized to determine stabilization energies (SE).
• Calculations were performed at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d) level of theory.

Main Results:

• Stabilization energies were calculated and compared with magnetic criteria (Lambda, NICS).
• Analysis of frontier orbitals, geometries, and proton affinities provided complementary evidence.
• Substrates were classified as antihomoaromatic, nonhomoaromatic, and homoaromatic.

Conclusions:

• The study successfully categorized various bicyclo[3.2.1]octane derivatives based on their homoaromatic character.
• Heteroatom substitution significantly influences the homoaromaticity of these systems.
• Specific substitutions lead to antihomoaromatic (BH, AlH, Be), nonhomoaromatic (O, S, NH, PH), and homoaromatic (S, PH, NH, O, ON) behaviors, with Mg showing transitional properties.