Ethynyldiazonium Ions: Possible Precursors for the Generation of C-sp-Centered Carbenium Ions? An ab Initio Study of the Linear, Unimolecular Dissociation of the Parent Ethynyldiazonium Ion


The thermal dediazoniation of ethynyldiazonium ions is examined as a possible reaction pathway for the generation of C-sp-centered carbenium ions, ethynyl cations RCC+. The possibility of the linear, unimolecular dissociation HCCNN+(1)→HCC+ (2) + N2 is discussed on the basis of the structures obtained at the HF/6-31G* and the MP2/6-31G* levels, the energies calculated at levels up to MP4(SDQ)/6-31G*//MP2/6-31G*, and electron density analysis of 1 and several states of 2 and compared to the dissociations of vinyldiazonium ion, 3, and methyldiazonium ion, 5. 2 has several singlet states [1Σ+(π2)≈ 1Π < 1Δ < 1Σ+(π4)] that are energetically close to the 3Π ground state. The 1Σ+4) state is correlated with the ground state of 1 by orbital symmetry. The primary reaction product, however, is 2 in its 1Σ+2) state due to the occurrence of an avoided crossing. The dissociation toward 2, 1Σ+2), is endothermic by 96.2 kcal mol-1 at the highest level. The activation barrier for the reaction is predicted to be closer to the binding energy of 150.2 kcal mol-1 between molecular nitrogen and 2, 1Σ+4), since the avoided crossing is associated with a late transition state. The theoretical results suggest that the intrinsic stability of 1 is such that dediazoniation does not occur.



International Standard Serial Number (ISSN)

0002-7863; 1520-5126

Document Type

Article - Journal

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© 1987 American Chemical Society (ACS), All rights reserved.

Publication Date

01 Jul 1987