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Target aryne

Target aryne
14 August 2015 - Image of the month

aryne AFM pavlicek 2015.PNGArynes are well established reactive intermediates in organic chemistry but if you are one of those people who believe something only when they see something you had to wait until 2015 when Avlivek et al. actually took an (AFM) image of one of them as reported in Nature Chemistry (DOI).

A specific naphtoperylene with two iodo substituents was selected as a precursor to an aryne. This molecule was then deposited on a layer of NACl on copper. A STM scan revealed the precise location of one molecule and then both iodine atoms were stripped from it by hovering the STM tip over them at a precise voltage. The report displays AFM images showing the perylene core with the two discarded iodine atoms at a distance. So what is to do next is comparing the AFM images of the aryne with a reference perylene that does not have the iodine substituents. The authors note that the aryne hexagon appears curved and that based on bond lengths and scan intensity (height) the resonance structure best representing the aryne is a cumulene rather than an alkyne or a diradical. Sanity check: the same AFM tip can reposition the iodine atoms on the perylene core proving that it is indeed an aryne.