Triphenylmethyl radical

Triphenylmethyl radical (also known as the trityl radical) is a type of organic radical that has played a significant role in the development of organic chemistry. It is represented by the chemical formula (C₆H₅)₃C•, where the "•" indicates the presence of an unpaired electron, characteristic of radicals. This radical was first synthesized and identified by Moses Gomberg in 1900, marking a pivotal moment in the understanding of free radicals in chemistry.

History

The discovery of the triphenylmethyl radical by Moses Gomberg at the University of Michigan in 1900 challenged the existing chemical dogma of the time. Gomberg attempted to prepare hexaphenylethane from triphenylmethyl chloride and silver, expecting to couple two triphenylmethyl groups. Instead, he isolated a stable, colorless solution that exhibited properties indicative of a free radical, fundamentally changing the understanding of organic chemistry and paving the way for the study of radical chemistry.

Structure and Properties

The triphenylmethyl radical is characterized by its three phenyl groups attached to a central carbon atom, which bears an unpaired electron. This structure imparts significant stability to the radical, unusual for free radicals at the time of its discovery. The stability is attributed to the delocalization of the unpaired electron over the phenyl rings, a concept that has been supported by various spectroscopic studies, including electron paramagnetic resonance (EPR) spectroscopy.

The radical is relatively stable at room temperature in the absence of air, but it dimerizes to form hexaphenylethane in the presence of oxygen or upon prolonged standing. This dimerization is a reversible process, and the radical can be regenerated by various means, such as exposure to light or heat.

Synthesis

The original synthesis of the triphenylmethyl radical by Gomberg involved the reaction of triphenylmethyl chloride with metallic silver. This process, known as the Gomberg-Bachmann reaction, has been refined over the years but remains a fundamental method for preparing the triphenylmethyl radical. Other methods include the homolysis of certain precursors under specific conditions, such as photolysis or thermolysis.

Applications

The triphenylmethyl radical has found applications in various areas of chemistry. It serves as a starting material for the synthesis of other organic radicals and compounds. In polymer chemistry, it has been used as an initiator for the polymerization of certain monomers. Additionally, its stability and reactivity have made it a valuable model compound in the study of radical reactions and mechanisms.

See Also

• Free radical
• Organic chemistry
• Moses Gomberg
• Electron paramagnetic resonance