The C₄H₅⁺ Potential Energy Surface. Structure, Relative Energies, and Enthalpies of Formation of Isomers of C₄H₅⁺

Abstract

The potential energy surface for C4H5 + as calculated by ab initio molecular orbital theory is reported at two levels of theory, HF/6-31G(d,p) and MP2(full)/6-311G(d,p). Fourteen minima have been located at HF/6-31G(d,p), but inclusion of electron correlation reduced this number to nine. The methylcyclopropenyl cation, 1, is the global minimum, and the 2-cyclobutenyl (2), α-vinylvinyl (3), γ-methylpropargyl (4), α-methylpropargyl (5), and 1-cyclobutenyl (6) cations are 9.1, 19.9, 25.3, 27.5, and 26.9 kcal/mol, respectively, above 1. Eleven transition structures, permitting interconversion between the nine minima, are reported. Enthalpies of formation (in kcal/mol) calculated at MP4SDTQ/6-311++G(2df,p) are 231.4 for 1, 241.7 for 2, 246.9 for 3, 255.7 for 5, 259.9 for 6, and 264.3 for 7.

Vacuum ultraviolet photoionization mass spectrometric study of cyclohexene

“…However, both cis ‐ and trans ‐ form of buta‐1,3‐dien‐4‐yl cation cannot be located at ω B97X‐D/6‐31+g(d,p) level. In a previous C 4 H 5 + PES study, Hopkinson and co‐workers found that trans ‐buta‐1,3‐dien‐4‐yl cation could be located only at HF level, but not at MP2 or MP4 level, and it can collapse into buta‐1,2‐dien‐4‐yl cation (CH 2 CHCCH 2 + ) via low barrier. Previous investigations about photodissociation of 1,3‐butadiene have also suggested that formation of buta‐1,2‐dien‐4‐yl is more favorable among the two possible channels to produce C 4 H 5 + from C 4 H 6 + .…”

Cyclopropenyl cation – the simplest Huckel's aromatic molecule – and its cyclic methyl derivatives in Titan's upper atmosphere

“…A number of minima and several transition structures permitting interconversion between the minima have been located on the potential energy surface. The methylcyclopropenyl cation is the global minimum (Cunje et al, 1996), and five other isomers are above the global minimum by 9.1 to 26.9 kcal/mol. Because of the existence of multiple minima on the potential energy landscape and substantial barriers to the isomerization processes, each isomer is trapped at the bottom of its corresponding minimum well without the possibility to convert to the lowest energy geometry.…”

“…The biggest hurdle (Ricks et al, 2010;Garand et al, 2008) in infrared and microwave spectroscopy experiments is to selectively study a sufficiently cold isomer of a molecular ion in an isolated condition, even if it is well demonstrated that rotational spectrometers based on jet expansion and Fourier Transform technique are able to characterize different conformers at the same time (Cocinero et al, 2012;Pena et al, 2012). As an example, the C 4 H 5 + potential energy surface (Cunje et al, 1996), as evaluated by ab initio computations, is highly complex. A number of minima and several transition structures permitting interconversion between the minima have been located on the potential energy surface.…”

Imaging the dynamics of ion–molecule reactions

“…The internally highly excited product ions further stabilize by the formation and elimination of molecular hydrogen. 116 In a third step, a hydrogen atom might be ejected from the C 4 H 3 +…”