Structure-activity relationship in the case of intramolecular ortho-cyclization of aromatic nitroso oxides: Inverted steric effect of substituent in the 2-R-C6H4NOO transformation |
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Authors: | Alfia R. Yusupova Ekaterina M. Chainikova Rustam L. Safiullin Sergey L. Khursan |
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Affiliation: | Ufa Institute of Chemistry, Ufa Federal Research Center of the Russian Academy of Sciences, Ufa, Russian Federation |
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Abstract: | A systematic theoretical study at the M06L/6-311+G(d, p) level of theory was carried out to calculate the activation barriers ΔH≠ for the intramolecular ortho-cyclization of aromatic nitroso oxides 2-R-C6H4NOO and to reveal the effect of substituent nature and position in the benzene ring on the nitroso oxides reactivity. A set of 24 substituents with widely differing spatial and electronic properties (inductive, resonant, steric effects of R) was studied. The para-substituent was shown to have little effect on the ΔH≠ value. The full set of effects of the R substituent contributes to the reactivity of ArNOO for 3-substituted aromatic nitroso oxides. In the case of 5-substituted ArNOO the Hammett-type relationship was obtain to describe inductive and resonant effects of R on the ortho-cyclization reactivity. The ortho-cyclization for 2-substituted nitroso oxides is a nontrivial example of the existence of an “inverted” steric effect, when an increase in substituent size accelerates intramolecular transformation. The substituent in position 6 also exhibits an “inverted” steric effect, but it is noticeably weaker than that for 2-R-C6H4NOO. |
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Keywords: | density functional theory intramolecular transformation inverted steric effect nitroso oxides ortho-cyclization |
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