Combined experimental and theoretical study of the C-H bond strength and the gas phase acidity of triacetylene, C6H2, and the electron affinity of the C6H. radical

✍ Scribed by Johannes Natterer; Wolfram Koch; Detlef Schröder; Norman Goldberg; Helmut Schwarz

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 670 KB
• Volume: 229
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(94)01075-7

✦ Synopsis

The thermochemistry of triacetylene, &H,, the corresponding neutral triacetylide radical, &H', and the triacetylide anion, C6H-, has been evaluated by combining mass spectrometric means with high-level ab initio MO calculations at the CCSD(T) level. Experimentally, the ion/molecule bracketing method has been applied to determine the gas phase acidity (AGacld) of &Hz as 347 ? 3 kcal/mol. For this purpose. C6H-anions were reacted with various bases for which AGacld is known. The computations lead to a dissociation energy of 126.8 i 1.6 kcal/mol for a C-H bond of triacetylene and an electron affinity of 3.69 rf-0.05 eV for the triacetylide radical C6H'. Combining the calculated figures in terms of a thermochemical cycle leads to a theoretical prediction of AGacld (298 K) = 346.7 rf-2.8 kcal/mol; this is in excellent agreement with the experimental value. The implications of the present results for interstellar chemistry are discussed.