Longest carbon–carbon bond yet pushes chemistry to its limits

The longest ever carbon–carbon bond has been created by researchers in Japan.1 At more than 1.8Å, this bond is longer than the maximum possible bond length calculated for certain alkanes and longer than the shortest non-bonding distance2 between two carbon atoms. ‘Looking for structures with particularly long or short bonds is telling us much about our current understanding of chemical bonding,’ says organic chemist Peter Schreiner from the University of Giessen, Germany, who wasn’t involved in the work. Pushing chemical bonds to their limits ‘urges us to keep asking the question: when is a bond a bond?’, he adds.Since 2011, Schreiner and colleagues held the record for the longest carbon–carbon bond – a 1.7Å alkane bond. Now, a team around Yusuke Ishigaki and Takanori Suzuki from Hokkaido University first computationally designed and then synthesised a compound featuring a bond 0.1Å longer – almost 1.2 times the length of a regular alkane carbon–carbon bond. This makes dispiro(dibenzo cycloheptatriene) derivative the neutral hydrocarbon with the longest single bond in existence.