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Structure‐activity relationship in the case of intramolecular ortho ‐cyclization of aromatic nitroso oxides: Inverted steric effect of substituent in the 2‐R‐C 6 H 4 NOO transformation
Author(s) -
Yusupova Alfia R.,
Chainikova Ekaterina M.,
Safiullin Rustam L.,
Khursan Sergey L.
Publication year - 2020
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.26094
Subject(s) - steric effects , substituent , chemistry , intramolecular force , reactivity (psychology) , nitroso , electronic effect , stereochemistry , ring (chemistry) , benzene , medicinal chemistry , computational chemistry , organic chemistry , medicine , alternative medicine , pathology
A systematic theoretical study at the M06L/6‐311+G(d, p) level of theory was carried out to calculate the activation barriers Δ H ≠ for the intramolecular ortho ‐cyclization of aromatic nitroso oxides 2‐R‐C 6 H 4 NOO 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 Δ H ≠ 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‐C 6 H 4 NOO.