Correlation between Hammett substituent constants and directly calculated pi-conjugation strength

Area of Science:

• Computational Chemistry
• Organic Chemistry
• Quantum Chemistry

Background:

• Benzylic cations and anions are key intermediates in organic reactions.
• Understanding substituent effects on electronic structure is crucial for predicting reactivity.
• Energy Decomposition Analysis (EDA) provides insights into bonding interactions.

Purpose of the Study:

• To investigate the electronic structure of substituted benzylic cations and anions.
• To analyze the pi bonding interactions between the benzylic carbon and the phenyl ring.
• To correlate these bonding properties with electronic substituent parameters.

Main Methods:

• Energy Decomposition Analysis (EDA) was performed on various substituted benzylic systems.
• Calculations included ortho-, meta-, and para-substituted benzylic cations and anions.
• The pi bonding component of the interaction was specifically examined.

Main Results:

• A linear correlation was observed between the calculated pi bonding values and Hammett constants.
• This correlation holds for substituents possessing pi orbitals.
• The strength of pi bonding is influenced by the electronic nature and position of the substituent (R).

Conclusions:

• The electronic effects of substituents on benzylic ions can be quantitatively described using Hammett constants.
• EDA provides a valuable tool for understanding bonding in substituted aromatic systems.
• This work offers a predictive model for the stability and reactivity of benzylic intermediates.