Homolytic C-O cleavage in phosphates and sulfonates

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Organic Chemistry

Background:

• Accurate calculation of bond dissociation enthalpies (BDEs) is crucial for understanding chemical reactivity.
• Various high-level ab initio and density functional theory (DFT) methods exist, but their reliability for C-O BDEs requires careful evaluation.

Purpose of the Study:

• To rigorously assess and identify the most accurate computational method for calculating C-O homolytic bond dissociation enthalpies.
• To investigate the substituent effects on the C-O BDEs of alkenyl and aryl phosphates/sulfonates using a validated high-accuracy method.

Main Methods:

• High-level ab initio calculations (G4, G3B3, G3, CBS-QB3).
• Density functional theory (DFT) methods, including wB97.
• Natural Bond Orbital (NBO) analysis.

Main Results:

• The wB97 method demonstrated the highest reliability for C-O BDEs with a root-mean-square deviation (RMSD) of 7.6 kJ/mol.
• Distinct substituent effects were observed for α- and β-substituted alkenyl phosphates/sulfonates.
• Excellent linear correlations were found between C-O BDEs and the σp(+) substituent constant for β-substituted alkenyl systems.

Conclusions:

• The wB97 method is recommended for accurate C-O BDE predictions.
• Substituent effects significantly influence C-O BDEs in phosphates and sulfonates, with variations between alkenyl and aryl systems.
• NBO analysis provides insights into the electronic origins of these substituent effects on C-O bond strength.