# Radical Stability Paradox: Substituent Effects versus Heats of Formation

## TL;DR

The paper resolves a paradox in radical chemistry by showing that substituent stability, not just their effects, influences radical stability.

## Contribution

A generalizable framework is introduced to extract intrinsic substituent effects from experimental and computational data.

## Key findings

- Tertiary radicals are more stable than primary ones due to substituent stability, not substituent effects.
- The heat of formation includes both substituent effects and substituent stability.
- A new method is proposed to disentangle these effects in radical chemistry.

## Abstract

Recently, we have shown that alkyl substituents destabilize the carbon radical center of organic radicals. However, seemingly in contradiction with this earlier finding, the series of isomeric n‐butyl, s‐butyl, and t‐butyl radicals shows an increasingly stable (less positive) heat of formation ∆H
f, despite an increasing number of alkyl substituents at the radical center. Herein, we provide a solution to this apparent paradox of contradicting pictures. The crux of the matter is that ∆H
f not only comprises the substituent effect on the radical center but also the intrinsic stability of the substituents. Furthermore, we provide a generalizable framework for extracting the actual intrinsic substituent effects from experimental and computational data, an approach with broad applicability to radical chemistry, thermochemistry, and beyond.

Rethinking molecular stability: Quantum‐chemical analyses show that the greater stability of tertiary over primary organic radicals is not caused by stabilizing substituent effects but by the inherent stability of the substituent.