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Introduction
Published in Harry Kroto, 60: Buckminsterfullerene, 2016
The Carbon Chain Pathway started in a totally different field with the development of organic synthetic techniques by David Walton at Sussex who created extended linear carbon chain structures called polyynes with alternating single and triple bonds30-32 and the study of the molecular dynamics of these chains by molecular spectroscopy (microwave rotational spectroscopy) in a collaboration between David and my spectroscopy group. In fact the key catalyst was a unique Chemistry by Thesis course, initiated by the then dean of the School of Molecular Sciences, Colin Eaborn. In this course chemistry undergraduates at the University of Sussex were able to obtain BSc degrees by carrying out research more or less full-time for ca. two years. The student involved in the study of the first cyanopolyyne HC5N, Anthony Alexander, did an outstanding job.33 When the rotational frequencies had been measured they were used in a collaboration between our Sussex group and Takeshi Oka, Lorne Avery, Norm Broten and John Macleod at the National Research Council (NRC) in Canada, and this resulted in the discovery by radioastronomy of the unexpectedly high abundance of HC5N in the interstellar medium.34* Then Colin Kirby, at the time a grad student, achieved the difficult synthesis of HC7N devised by David and measured its spectrum35 which enabled us to detect it in space.36 Then using the frequencies Takeshi imaginatively predicted the frequency of HC9N and we detected it as well.37 It was this series of Sussex/NRC laboratory and radioastronomy studies which uncovered the, at the time amazing, abundance of the long carbon chain molecules in space. The next step in the story was the detection by Eric Becklin, Gerry Neugebauer and their coworkers of an amazing object emitting infrared radiation an order of magnitude greater than
Conformational stability of cyclopropanecarboxaldehyde is ruled by vibrational effects
Published in Molecular Physics, 2021
Silvia Alessandrini, Mattia Melosso, Ningjing Jiang, Luca Bizzocchi, Luca Dore, Cristina Puzzarini
Experiments offer the opportunity to look into the relative conformers population in a sample via measurable quantities. In the field of spectroscopy, with particular reference to rotational and/or vibrational spectroscopic techniques, the intensity of transition lines can be used to identify the most stable species. Rotational spectroscopy can only be carried in the gas phase, while infrared and Raman spectroscopies can handle both condensed and gaseous sample. However, the high resolution required for obtaining good estimates of line intensities is achievable only in gas-phase experiments [5,6]. As in the case of line positions, experimental determinations often need to be supported and/or complemented by quantum-chemical calculations. In the present case, the analysis of the PES allows the identification of all possible conformers and of the TSs ruling their interconversion, and thus permits the estimate of the corresponding rotational barriers [6–9]. Overall, quantum-chemical computations allow the theoretical derivation of the relative abundances of each conformer at a given temperature. The interplay of experiment and theory is crucial whenever experiments alone are unable to reveal the observed conformer, as shown – for example – in Refs.[6,10–12].