Methyl Radical Addition Reactions to C═X Double Bonds.

Area of Science:

• Organic Chemistry
• Computational Chemistry
• Physical Chemistry

Background:

• Radical additions are vital for forming carbon-carbon and carbon-heteroatom bonds.
• Understanding periodic trends in reactivity is crucial for designing new synthetic pathways.

Purpose of the Study:

• To systematically investigate methyl radical additions to various π-systems using DFT.
• To elucidate periodic trends in reaction barriers, energies, and regioselectivity.

Main Methods:

• Density Functional Theory (DFT) calculations employing ZORA-(U)OLYP/TZ2P.
• Systematic variation of the substituent X in H₂C═X across groups 14, 15, and 16.
• Analysis of orbital interactions and Pauli repulsion.

Main Results:

• Addition barriers at carbon decrease, while barriers at X increase from tetrels to chalcogens.
• Reaction energies become less favorable across a period but more favorable down a group.
• Regioselectivity favors addition at X, except for CH₂, NH, and O, where carbon attack dominates.

Conclusions:

• Clear periodic trends in methyl radical addition reactions were identified.
• Pauli repulsion is a critical, often overlooked, factor influencing radical reactivity and regioselectivity.
• The findings provide valuable insights for predicting and controlling radical addition reactions in π-systems.