Nathan P. Bowling, R. J. Halter, J. Hodges
Feb 21, 2006
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0
Influential Citations
52
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Journal
Journal of the American Chemical Society
Abstract
1-Diazo-2,4-pentadiyne (6a), along with both monodeuterio isotopomers 6b and 6c, has been synthesized via a route that proceeds through diacetylene, 2,4-pentadiynal, and 2,4-pentadiynal tosylhydrazone. Photolysis of diazo compounds 6a−c (λ > 444 nm; Ar or N2, 10 K) generates triplet carbenes HC5H (1) and HC5D (1-d), which have been characterized by IR, EPR, and UV/vis spectroscopy. Although many resonance structures contribute to the resonance hybrid for this highly unsaturated carbon-chain molecule, experiment and theory reveal that the structure is best depicted in terms of the dominant resonance contributor of penta-1,4-diyn-3-ylidene (diethynylcarbene, H−C⋮C−C−C⋮C−H). Theory predicts an axially symmetric (D∞h) structure and a triplet electronic ground state for 1 (CCSD(T)/ANO). Experimental IR frequencies and isotope shifts are in good agreement with computed values. The triplet EPR spectrum of 1 (|D/hc| = 0.6157 cm-1, |E/hc| = 0.0006 cm-1) is consistent with an axially symmetric structure, and the C...