Kinetic application of electron paramagnetic resonance spectroscopy. IX. Preparation and properties of di-tert-butyliminoxy

Abstract

2.1.0]pentane which was recrystallized from ethanol to give 31.0 mg of the pure compound, mp 179-180°. Fractions 142-166 contained 172 mg of starting diene whose nmr spectrum showed no deuterium scrambling within experimental error.The nmr (CCL) of the deuterated vinylcyclopropane consisted of r 8.50 (m, cyclopropyl CH2. rel area 45), 7.64 (m, cyclopropyl CH, rel area 28), 4.84 (d, / = 10 cps, vinyl, rel area 9.4). The nmr (CC14) of the deuterated bicyclo[2.1.0]pentane consisted of 7.82 (d, J = 12 cps, rel area 70), 7.40 id, J = 12 cps, rel area 66), 6.98 (s, rel area 18).A second identical run gave the following results: vinylcyclopropane, nmr (CC14) 8.50 (m, cyclopropyl CH2, rel area 40), 7.64 (m, cyclopropyl CH, rel area 26), 4.84 (d, J = 10 cps, vinyl, rel area 10); bicyclo[2.1.0]pentane, nmr (CC14) 7.82 (d, / = 12 cps, rel area 50), 7.40 (d, J = 12 cps, rel area 45), 6.98 (s, rel area 12).Catalytic Reduction of Deuterio-2,2,5,5-tetraphenylbicyclo[2.1.0]pentane. A sample of deuterio-2,2,5,5-tetraphenylbicyclo[2.1.0]pentane obtained from photolysis of deuterated 1,1,5,5-tetraphenyl-1.4-pentadiene was catalytically reduced with 10% palladium on charcoal as described above. The nmr (CC14) indicated 7.57 (s, C-4 and C-5 CH2, rel area 23) and 6.20 (s, C-2 CH2, rel area 8.5).

Spectral and kinetic measurements on a series of persistent iminoxyl radicals

“…In striking contrast, radical 8 on standing gave about 4% pivalonitrile and 40% di-tert-butyl ketone. 4 A possible decay sequence for the radical, constistent with the limited evidence, is given in Scheme 2.…”

“…2,4 The conversion of oximes to ketones with oxides of nitrogen, during which iminoxyls are likely intermediates, is regarded as a standard synthetic transformation. 5 Head-to-tail dimerization as shown below is the exclusive pathway in the initial stages for di-tert-butyl ketiminoxyl (8), 4 and probably also for bis(1-adamantyl) ketiminoxyl. 6 …”

The Only Stable Organic Sigma Radicals: Di‐ tert ‐Alkyliminoxyls

“…Yield of di-tert-butyl ketoxime: 3.3 g (46 %). 19 Some 24 years later, a simpler and more elegant synthesis of this ketoxime (and other symmetric di-tertalkyl ketoximes) was developed by Mendenhall and coworkers (Equation 6.7). 20 In their new procedure the alkylating agent was generated in situ from sodium and the tertiary chloride, thus conveniently avoiding expensive, pyrophoric reagents.…”

“…Di-tert-Butyliminoxyl is a blue liquid, freezing point −21 • C, n 294K D 1.4452, d 295K 0.824, with a weak absorption extending from about 530 nm to beyond 800 nm, ε(800 nm) = 5.1 in benzene, 5.0 in 95 % ethanol, and 4.7 in cyclohexane. 19 The IR spectrum shows an intense absorption at 1610 cm −1 from C=N and/or N-O stretching vibrations. A peak at 1650 cm −1 in the parent ketoxime (C=N vibration) does not appear in the spectrum of the radical.…”

“…For example, at 23 • C (Me 3 C) 2 C=NO • has a N = 31.32 G in benzene and 31.55 G in acetic acid, whereas (Me 3 C) 2 NO • has a N = 15.44 G in benzene and 16.46 in acetic acid. 19 The lack of a significant solvent effects on both the EPR and visible spectra can be rationalized by noting that the nitrogen atom in the iminoxyl is approximately sp 2 hybridized and is, therefore, less polarizable and less basic than the sp 3 hybridized nitrogen atom in the nitroxide. The orbital energies and electron distribution in the iminoxyl are, therefore, less affected by a change in solvent polarity than is the case for the nitroxide.…”