Theoretical Study of the Structure and the Physico Chemical Properties of 1,2‐Benzyne

Abstract

IJne estimation du taux de fragmentation montrc qu'i 70 cV, 60 i 65% des ions butyle form& dans la source se dkcomposent avant de parvenir sur le collecteur. L'importance de cettc fraction ne dCpend que t r k peu de la structure originale des ions C4H,+. 1 . Theoretical Study of the Structure and the Physic0 Chemical Properties of 1,2-BenzyneSummary. The structure of 1,2-benzyne (I) has been optimized with respect to its total molecular energy using the MINDOjZ SCF-procedure. The results indicate a bond length of -1.26 A for the strained triple bond. The overall geometry suggests that I possesses considerable resonance energy. The calculated heat of formation (dHf(1) = 107 kcal/mole) is in good agrecincnt with an estimate from mass spectrometric studies (AHfexP(I) = 118 & 5 kcal/mole). From model calcula-

Electronic States of 1,5‐Cyclooctadiyne Radical Cation and of Related Systems: The electronic structure of cis‐bent carbon‐carbon triple bonds

“…An important assumption underlying the above argument is that the orbitals la,(n), 3a,(CC-a) for the C2h system and lb,(n), 4al(CC-a) for the C z v system are almost accidentally degenerate for 8 = go", as suggested by the theoretical results obtained by Haselbach [14]. It should be mentioned that the argument embodied in (3) is similar to the one given by Gimarc [15] for the dependence on 8 of the orbital energies of diimidc.…”

“…Model calculations which show the influence of bending on the orbital structure of acetylene HCC-angle = n-8 have been performed by Hoffmavzn, Imamura & Hehre [lll using the Extended Hiickel Theory [12] and more recently with the MINDO/Z procedure [13] by Haselbach [14] in the course of a theorctical investigation of 1,Zbenzyne (9). Their arguments can be summarized qualitatively as shown in (3) The rationalization suggested is that a trans-bend (Dah -+ Czh) will lead to a lowering of the in-plane component of le,(n), which for an angle 8 = 90" will end up as the out-of-phase linear combination 3 b,(CH-a) of the CH-a-orbitals, whereas the 3ag(4 orbital of acetylene becomes the 3a,(CC-o) of the bent model system.…”

Normal coordinates, structure, and bonding of benzyne

“…The bond lengths and bond orders of benzyne were first estimated previously in connection with semiempirical theoretical calculations.6 Some calculations indicate a shortening of the C1-C2 bond and lengthening of the C4-C5 bond, and a "triple bond" structure, although one calculation suggests a cumulene-like structure. 7 The only experimental hints directly cogent to the geometry and bonding of benzyne come from the infrared spectrum of the species frozen in an inert matrix. This spectrum was obtained by Chapman, Mattes, McIntosh, Pacansky, Calder, and Orr.8 The microwave spectrum has not been reported and the electronic spectrum9 appears to consist of a featureless continuum whose energy range and intensity are consistent with the interpretation just given for the "triple" bond, that the "in-plane" carbon orbitals form ethylene-like bonding and antibonding orbitals whose bonding and antibonding strength are both significantly weaker than in a normal 2pir olefinic bond.…”