TY - JOUR
T1 - Insights into unusual stability of 5-membered-ring endocyclic benzyl carbocations in aqueous solution
AU - Sung, Robert
AU - Sung, Kuangsen
N1 - Funding Information:
We thank National Science Council of Taiwan for financial support (NSC104‐2119‐M‐006‐013) and National Center for High‐Performance Computing for computer facilities and time.
Publisher Copyright:
Copyright © 2018 John Wiley & Sons, Ltd.
PY - 2018/10
Y1 - 2018/10
N2 - The acyclic o-oxygen benzyl carbocation 1, the 6-membered-ring endocyclic o-oxygen benzyl carbocation 2, and the 5-membered-ring endocyclic o-oxygen benzyl carbocation 3 were used as model compounds to get insights into the general phenomenon for the unusual stability of the 5-membered-ring endocyclic benzyl carbocations in aqueous solution. The hydride-ion affinities of 1, 2, and 3 in gas phase, acetonitrile, and DMSO were calculated and compared by the density functional theory method, and 3 isodesmic reactions were designed to confirm their thermodynamic stability. What we found is that the 5-membered-ring endocyclic o-oxygen stabilizes the benzyl carbocation 3 less than the acyclic o-oxygen stabilizes the benzyl carbocation 1 in gas phase because of ring strain and through-bond induction. However, the high solvation energies of the 5-membered-ring endocyclic o-oxygen benzyl carbocation 3 not only offset the destabilizing effects of ring strain and through-bond induction but also make it even more stable than the acyclic o-oxygen benzyl carbocation 1 in polar solvents like acetonitrile, DMSO, and water.
AB - The acyclic o-oxygen benzyl carbocation 1, the 6-membered-ring endocyclic o-oxygen benzyl carbocation 2, and the 5-membered-ring endocyclic o-oxygen benzyl carbocation 3 were used as model compounds to get insights into the general phenomenon for the unusual stability of the 5-membered-ring endocyclic benzyl carbocations in aqueous solution. The hydride-ion affinities of 1, 2, and 3 in gas phase, acetonitrile, and DMSO were calculated and compared by the density functional theory method, and 3 isodesmic reactions were designed to confirm their thermodynamic stability. What we found is that the 5-membered-ring endocyclic o-oxygen stabilizes the benzyl carbocation 3 less than the acyclic o-oxygen stabilizes the benzyl carbocation 1 in gas phase because of ring strain and through-bond induction. However, the high solvation energies of the 5-membered-ring endocyclic o-oxygen benzyl carbocation 3 not only offset the destabilizing effects of ring strain and through-bond induction but also make it even more stable than the acyclic o-oxygen benzyl carbocation 1 in polar solvents like acetonitrile, DMSO, and water.
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U2 - 10.1002/poc.3863
DO - 10.1002/poc.3863
M3 - Article
AN - SCOPUS:85054327558
VL - 31
JO - Journal of Physical Organic Chemistry
JF - Journal of Physical Organic Chemistry
SN - 0894-3230
IS - 10
M1 - e3863
ER -