Emory chemists reveal challenge to reaction theory

Dec 17, 2004

For nearly 75 years, transition-state theory has guided chemists in how they view the way chemical reactions proceed. Recent research by Emory University chemists is challenging the long-held theory, showing that in some cases chemical reactions can proceed via a path that completely bypasses the "transition state."

"Our understanding of chemical reactions rests on the notion of the transition state. If we think of reactions as occurring on an energy landscape, the transition state is the 'mountain pass' separating the reactants, and the resulting products from the reaction are valleys," says Joel Bowman, an Emory theoretical chemist and chairman of the chemistry department.

According to transition state theory, reactions proceed over this mountain pass, Bowman says, "but our results for a well-studied chemical reaction show that the reaction occurs during the transition state -- and also through a surprising second path that is not near this transition state region."

Bowman's research, done in collaboration with physical chemist Arthur Suits of Wayne State University in Detroit, was published in the Nov. 12 issue of the journal Science, and was highlighted in the Nov. 15 issue of Chemical and Engineering News.

Using high-powered computational work and detailed experimental studies, the scientists demonstrated that formaldehyde (H2CO) exposed to light rays (or photoexcited) can decompose to hydrogen and carbon monoxide via a path that skirts that reaction's well-established transition state entirely.

Using detailed pictures and measurements developed by Suits, Bowman performed high-level calculations to create a "movie" of this second pathway. The visual model reveals that one of formaldehyde's hydrogen atoms breaks off and roams around before bumping into the second hydrogen atom and forming a hydrogen molecule (H2). At no point in this second pathway does the reaction go through its transition state.

Formaldehyde decomposition has long been a model system for those studying transition-state theory because the reaction is simple enough to treat with high-level theoretical models, and the products are easily detectable. Bowman's research shows that such transition-state-skirting pathways may not be all that unusual in other chemical reactions.

"Although this discovery does not overturn traditional transition-state theory, our work is part of a growing body of evidence that is changing and expanding the way chemists and biochemists think about chemical reactions," Bowman says.

Source: Emory University Health Sciences Center

Explore further: The stapes of a neanderthal child points to the anatomical differences with our species

add to favorites email to friend print save as pdf

Related Stories

Unexplained warm layer discovered in Venus' atmosphere

15 hours ago

A group of Russian, European and American scientists have found a warm layer in Venus' atmosphere, the nature of which is still unknown. The researchers made the discovery when compiling a temperature map ...

Manganese speeds up honey bees

Mar 24, 2015

Asked to name one way people have changed the environment, many people would probably say "global warming." But that's really just the start of it.

Supersonic electrons could produce future solar fuel

Mar 02, 2015

Researchers from institutions including Lund University have taken a step closer to producing solar fuel using artificial photosynthesis. In a new study, they have successfully tracked the electrons' rapid transit through ...

Recommended for you

Destroyed Mosul artefacts to be rebuilt in 3D

9 hours ago

It didn't take long for the scientific community to react. Two weeks after the sacking of the 300 year-old Mosul Museum by a group of ISIS extremists went viral on Youtube, researchers from the ITN-DCH, IAPP ...

Boys plagiarise more than girls at school

10 hours ago

Research by the University of the Balearic Islands has analysed the phenomenon of academic plagiarism among secondary school students. The study, published in the journal Comunicar, confirms that this practi ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.