A mechanistic study of the carbocation route from tetrahydrodicyclopentadiene to the adamantane ring

Abstract

. Can. J. Chem. 71, 2016Chem. 71, (1993. The energy profile for the transformation of the endo-tetrahydrodicyclopentadienyl cation A into the 1-adamantyl cation R has been probed by means of six separate experiments employing superacid techniques. Of the approximately 14 cations between A and R , required as intermediates for the above transformation, it can be shown that only one of these is capable of direct observation. This cation, the tricyclo[5.2.1.03~8]dec-3-yl (homobrendyl) cation J , is characterized in detail in one of the six experiments. The rate of the rearrangement of J into the 1-adamantyl cation has been measured. Cation J also undergoes a degenerate rearrangement, the dynamics of which can be probed using NMR line-broadening and selective inversion-recovery experiments. The relationship between the exo and endo tetrahydrodicyclopentadienyl cations D and A has been studied. Only A is directly observable, even though in some experiments direct precursors of D were used as cation sources. Several experimental probes were made in an attempt to detect the presence of a small equilibrium concentration of D, without success, and a rationale is provided for the much greater stability of A vs. D. The remaining four experiments involved the addition of neutral precursors to superacid solutions, but the initially formed (expected) cations could not be observed, only cations A, J, or R being observed instead. These "partitioning3'-type experiments prove whether the corresponding left-hand or right-hand transition-state barriers are the lower in energy. In the case of starting with transient cation intermediate E, only observable cation J is obtained, showing that the barrier between B and E is the high point on the overall carbocation reaction profile. sans succks plusieurs sondes expkrimentales; on presente une rationalisation de la stabilite beaucoup plus grande de A par rapport a D. Les quatre dernikres expkriences impliquent ['addition de precurseurs neutres a des solutions de superacides; lorsque les cations formes (attendus) initialement n'ont pu &tre observes, seuls les cations A, J ou R ont etC observes. Ces expkriences de <<partition>> ont permis de determiner si les bamkres <<gauche>> ou <<droites correspondantes sont d'energie plus basse. Dans le cas ou le cation transitoire intermediaire est le E, le seul cation observable est le J ; ce resultat dkmontre que la barri6re entre les cations B et E est un maximum sur le profil reactionnel global du carbocation.[Traduit par la redaction] IntroductionAdamantane 1 is produced commercially by the rearrangement of tetrahydrodicyclopentadiene 2 using strong Lewis acid catalysts and a hydride transfer initiator. T h e reactive intermediates in this process are carbocations, and the overall reaction is "driven" by the thermodynamic stability skeleton by converting all o f the starting skeleton 2 to an observable carbocation, and this has also been shown to rearrange to the 1-adamantyl cation (1, 2). In this case, almost all of the organic material exists ...

The Historic Camphenyl Cation: A Detailed Structure Evaluation Including Solvation Energy Calculations

“…We would like to re-open a discussion of the camphenyl chloride 2 −isobornyl chloride 3 rearrangement because of two recent developments: (1) Theoretical calculations , have shown that the secondary isobornyl cation in Meerwein's proposal does not exist as a stationary point on the camphenyl−isobornyl cation potential energy (PE) surface. (2) Any camphenyl chloride 2 → isobornyl chloride 3 mechanism must account for both a C−C bond shift and a chlorine atom shift.…”

Quadricyclane hydration kinetics in natural waters

“…Lajunen and Hirvonen [8] proposed an unspecified carbocation intermediate in norbornadiene hydration. Detection of bridged carbocations in water may not be possible with current techniques, as indicated by the need for nonpolar solvents and low temperature (−78°C) required to detect adamantane carbocations [10]. Hydration of the carbocations appears rate limiting since the observed similarity of hydration rates of quadricyclane and norbornadiene indicates that protonation and carbocation formation is rapid relative to hydration.…”

Applications of noisy quantum computing and quantum error mitigation to “adamantaneland”: a benchmarking study for quantum chemistry

“…The molecules studied in this work are the isomers of C 10 H 16 (isomer set) and carbocationic rearrangements involving C 10 H 15 + (reaction set), shown in Tables 1 and 2. The isomers and chemical reactions selected for quantum chemical modeling were inspired by the earlier works of Engler et al 74 and Kirchen et al 75 These two earlier works highlight the efforts in the 1970s on adamantane isomers and substituted adamantanes through both experimental thermochemistry and computational molecular mechanics, which led to great improvements in both techniques. 76,77 In the work of Engler et al , the relative stabilities of C 10 H 16 isomers were calculated using a molecular mechanics force field while deducing the favorable reaction pathway from the endo -tetrahydrodicyclopentadiene molecule to the adamantane molecule.…”

“…The barrier height energies tabulated in Table 2 for CBS-QB3 (Δ E ‡ CBS-QB3 ) and L-W1X (Δ E ‡ L-W1X ) methods were calculated as the energetic difference between the transition state structure and reactant (for forward reaction) and transition state structure and product (for reverse reaction). Note that the data shown in Tables 1 and 2 serve as an update to computational data calculated using a force field in the work of Engler et al 74 and qualitative experimental data without any computational transition state modeling in the work of Kirchen et al 75 In particular, our high-level data present an improved energy ordering (low to high) compared to the earlier force field work of Engler and co-workers, as follows: 1 , 3 , 12 , 19 , syn - 5 , 18 , 4 , exo - 2 , exo - 8 , 13 , 14 , endo - 2 , anti - 11 , 10 , 7 , endo - 8 , 9 , syn - 11 , anti - 6 , and anti - 5 .…”