Mapping the Triplet Potential Energy Surface of 1-Methyl-8-nitronaphthalene
journal contributionposted on 2005-07-22, 00:00 authored by Svetlana V. Kombarova, Yuri V. Il'ichev
Spin-unrestricted calculations and time-dependent DFT were used to characterize structure and reactivity of 1-methyl-8-nitronaphthalene (1) in the triplet state. Four hybrid models (B3LYP, PBE0, MPW1K, BHLYP) with significantly different amount of the exact exchange were employed. The triplet potential energy surface of 1 was mapped by using the UB3LYP and UMPW1K techniques. Both hybrid models provided qualitatively consistent pictures for the potential energy landscape. Thirty-one stationary points, of which 15 were minima, were found at the UB3LYP level of theory. Three minima corresponding to the nitro form of 1 were located on the triplet surface; just one was found for the singlet ground state. Two reaction paths leading from 1 either to a nitrite-type intermediate (2) or to the aci-form (3) were characterized. For both paths, reaction products were of diradical nature. The lower activation energy was obtained for the triplet-state tautomerization affording 3. The ground state of triplet multiplicity was predicted for two isomers of the aci-form. The triplet diradical 3 is expected to react through the thermal population of a close-lying singlet excited state. The results are discussed in relation to mechanisms of photoinduced rearrangements of peri-substituted nitronaphthalenes that can be used to develop novel photolabile protecting groups.
triplet surfacetriplet statenitro formUB 3LYPEnergy Surfaceenergy surfacesinglet ground statephotoinduced rearrangementsPBEaciminimaUB 3LYP levelground stateBHLYPdiradical naturetriplet multiplicityDFTnovel photolabilereaction pathsreaction productsactivation energyenergy landscapemodeltriplet diradical 3UMPW 1K techniques