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Intramolecular exchange coupling of arylnitrenes by OXYGEN
Author(s) -
Minato Masaki,
Lahti Paul M.
Publication year - 1994
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.610070905
Subject(s) - chemistry , excited state , ground state , electron paramagnetic resonance , singlet state , intramolecular force , ether , resonance (particle physics) , crystallography , photochemistry , nuclear magnetic resonance , atomic physics , stereochemistry , physics , organic chemistry
A series of m , n ′‐diazidodiphenyl ethers ( m ≤ n, m = 3,4; n = 3,4) was photolyzed at 77 K in frozen, glassy 2‐methyltetrahydrofuran matrices to generate the corresponding diphenyl ether m , n ′‐dinitrenes for study by electron spin resonance (ESR) spectroscopy. 3,4′‐Diazidodiphenyl ether gave an ESR spectrum dominated by a mononitrene peak with ∣ D / hc ∣ = 0·972 cm −1 , and also showed a weak dinitrene quintet spectrum with ∣ D / hc ∣ = 0·162 cm −1 having ESR spectral intensity vs temperature dependence (Curie law) consistent with either a high‐spin ground state or a very small singlet–quintet gap. Di(3‐azidophenyl) ether gave a strong mononitrene peak with ∣ D / hc ∣ = 0·996 cm −1 and a quintet dinitrene ESR spectrum (∣ D / hc ∣ = 0·162 cm −1 ) which exhibited non‐linear Curie law intensity behavior consistent with the quintet being a thermally populated excited state 40 cal mol −1 above a singlet ground state. Di(4‐azidophenyl) ether gave a strong mononitrene peak with ∣ D / hc ∣ = 0·961 cm −1 , but no observable spectrum related to a high‐spin open‐shell dinitrene. The results are consistent with oxygen being a weak exchange coupling linker in pi‐conjugated open‐shell molecules. The observed ground‐state spin multiplicities are in accord with qualitative superexchange and connectivity models, despite any perturbations due to resonance effects between the oxygen linker and p ‐nitrene sites.