UGA researcher discovers new driving force chemical reactions

UGA researcher discovers a new driving force for chemical reactions

1:58 PM, 22nd June 2011
UGA researcher discovers a new driving force for chemical reactions

ATHENS, US: New research published in the journal Science by a team of chemists at the University of Georgia and colleagues in Germany shows for the first time that a mechanism called tunneling control may drive chemical reactions in directions unexpected from traditional theories.

The finding has the potential to change how scientists understand and devise reactions in everything from materials science to biochemistry.

The discovery was a complete surprise and came following the first successful isolation of a long-elusive molecule called methylhydroxycarbene by the research team. While the team was pleased that it had “trapped” the prized compound in solid argon through an extremely low-temperature experiment, they were surprised when it vanished within a few hours. That prompted UGA theoretical chemistry professor Wesley Allen to conduct large scale, state-of-the-art computations to solve the mystery.

“What we found was that the change was being controlled by a process called quantum mechanical tunneling,” said Allen, “And we found that tunneling can supersede the traditional chemical reactivity processes of kinetic and thermodynamic control. We weren’t expecting this at all.”

What had happened? Clearly, a chemical reaction had taken place, but only inert argon atoms surrounded the compound, and essentially no thermal energy was available to create new molecular arrangements. Moreover, said Allen, “The observed product of the reaction, acetaldehyde, is the least likely outcome among conceivable possibilities.”

Other authors of the paper include Professor Peter Schreiner and his group members Hans Peter Reisenauer, David Ley and Dennis Gerbig of the Justus-Liebig University in Giessen, Germany. Graduate student Chia-Hua Wu at UGA undertook the theoretical work with Allen.

“We knew that the rate of a reaction can be significantly affected by quantum mechanical tunneling,” said Allen. “It becomes especially important at low temperatures and for reactions involving light atoms. What we discovered here is that tunneling can dominate a reaction mechanism sufficiently to redirect the outcome away from traditional kinetic control. Tunneling can cause a reaction that does not have the lowest activation barriers to occur exclusively.” 

The fact that new ideas about tunneling came from the isolation of methylhydroxycarbene was the kind of serendipity that runs through the history of science. Schreiner and his team had snagged the elusive compound, and that was reason enough to celebrate, Allen said. But the surprising observation that it vanished within a few hours raised new questions that led to even more interesting scientific discoveries.           

While the process was unearthed for the specific case of methylhydroxycarbene at extremely low temperatures, Allen said that tunneling control “Can be a general phenomenon, especially if hydrogen transfer is involved and such processes need not be restricted to cryogenic temperatures.”

Allen’s research was funded by the US Department of Energy.

(C) University of Georgia News

 

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