Carbon-carbon covalent bonds far more flexible than presumed

Date:
October 1, 2020
Source:
Hokkaido University
Summary:
A research group has successfully demonstrated that carbon-carbon
(C-C) covalent bonds expand and contract flexibly in response to
light and heat. This unexpected flexibility of C-C bonds could
confer new properties to organic compounds.



FULL STORY ==========================================================================
A Hokkaido University research group has successfully demonstrated that
carbon- carbon (C-C) covalent bonds expand and contract flexibly in
response to light and heat. This unexpected flexibility of C-C bonds
could confer new properties to organic compounds.


========================================================================== Rigid and robust, C-C covalent bonds are the most basic structure in
organic and biological compounds. Understanding their nature is essential
to improving our knowledge of chemical phenomena.

Usually, the C-C bond length is almost constant. The researchers, however, conducted this study on the premise that extremely elongated C-C bonds are weak, and so can expand or contract in response to external stimuli. The
group designed and synthesized compounds that cyclize to form cage-like structures when exposed to light. They investigated how the structural transformation influences the length of C-C bonds at compounds' cores.

The researchers found that the C-C single bonds at the core contract
flexibly during photocyclization. They also found that the cyclization
can be reversed by heating, and the C-C bonds expand as the compounds
return to the original state. Using single crystals of the compounds as
analogs made it possible for the researchers to directly observe their flexibility and easily elucidate their structure in detail.

This is the first time the process of expansion and contraction of C-C
bonds has been directly observed. The scientists concluded that this
is a new phenomenon, in which C-C bonds obtained flexibility when they
were elongated to the limit, decreasing the bonding energy. Furthermore,
they showed that the oxidation potential of the compound changed by
more than 1 volt due to the reversible expansion and contraction of the extremely elongated C-C bond, suggesting a new property related to the
bond's flexibility.

The researchers say that synthesizing compounds with even longer bonds
may lead to more functions through unique responses or major changes
in their properties. This challenging research, aimed at breaking the
record for the length of the C-C single bond, plays a role in developing materials that can be activated/deactivated by a novel response mode.

The researchers are Takuya Shimajiri, Professor Takanori Suzuki and
Assistant Professor Yusuke Ishigaki of Hokkaido University's Department
of Chemistry. The results of their study were published in Angewandte
Chemie International Edition on September 30, 2020. This work follows
their study in 2018, in which the group synthesized an organic compound
with a record C-C bond length of more than 0.18 nanometers, compared to
the standard 0.154 nanometers.


========================================================================== Story Source: Materials provided by Hokkaido_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Takuya Shimajiri, Takanori Suzuki, Yusuke Ishigaki. Flexible
C-C Bonds:
Reversible Expansion, Contraction, Formation, and Scission of
Extremely Elongated Single Bonds. Angewandte Chemie International
Edition, 2020; DOI: 10.1002/anie.202010615 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201001113537.htm

--- up 5 weeks, 3 days, 6 hours, 50 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)