Flash photolytic decomposition of aryl azides. Measurement of an intramolecular closure rate

Abstract

alkyl and alkyl-oxygen nonbonding interactions that are greater in the hydroxylamines and oximes than in the corresponding radicals, since the latter have a more open geometry. In addition, nonbonding interactions involving the hydrogen that is removed are eliminated.These steric effects on the O-H bond strength should be at a maximum with di-/er?-butyl nitroxide23 in which the relevant CNC angle is 136°and the CNO angle is 112°. In the hydroxylamine, if the nitrogen is tetrahedral, the angles will be 108°. Unfortunately ditert-butyl nitroxide reacted so slowly with hydrazobenzene in CC14 and in benzene that the heat of the reaction could not be determined. The slowness of reaction suggests that the O-H bond strength in this compound is several kcal/mole less than in 1, since the sterically more hindered but thermoneutral hydrogen transfer from di-?er/-butylhydroxylamine has a rate constant of over 102 M~l sec-1 in CC14 at room temperature.31The importance of steric factors in determining the O-H bond strength in 1 is difficult to estimate. However, the six-membered ring should inhibit any large changes in the CNC angle on going from the hydroxylamine to the radical, so steric effects are probably small. It is interesting to note that the nitrogen hyperfine splitting for 1 in most solvents is similar to the values found for many less substituted and unstable, dialkyl nitroxides. In these radicals the alkyl groups are free to adopt a conformation minimizing steric interactions. We would accordingly predict that the O-H bond strengths in unhindered dialkylhydroxylamines are in the range 72-74 kcal/mol.Steric effects should be absent in the bicyclic nitroxides 3 and 4.

Direct Modulation of Microtubule Stability Contributes to Anthracene General Anesthesia

“…The UV–vis spectrum of 1-AZA displays a pronounced triple absorption peak (λ abs = 350–400 nm), corresponding to the azido moiety (Figure S2b), and an extinction coefficient was determined at 372 nm: ε 372 = 9100 M −1 cm −1 . Complete photolysis of the azide via UV transilluminator or near-UV laser exposure occurred rapidly, consistent with previous studies on aryl azides, 21 with the transient product containing a reactive nitrene 12 capable of protein attachment. 20 The chemistry of aryl azides as protein photolabels has been extensively investigated.…”

Recent Advances in Iron‐Catalyzed C—H Bond Amination via Iron Imido Intermediate

“…This mechanism parallels with that of noncatalytic thermal-or photo-induced conversion of aryl azides to carbazoles. [86][87][88][89][90] Accordingly, the [Bu the C(sp 2 )-H bond amination reactions. [85] The subtle difference is having higher temperature (120 o C vs. 100 o C), and the use of a mixed solvent of DMF with ClCH 2 CH 2 Cl.…”

Photochemical Rearrangements and Fragmentations of Benzene Derivatives and Annelated Arenes

“…Arenes, which are condensed to carbo-or heterocyclic rings, may undergo P-cleavage followed by ring enlargement via widely differing mechanisms. The reaction of (225) proceeds at 77 K to give initially electronically excited (5) (apparently adiabatic reaction), because product fluorescence n [more intense than that of (225)l and product phosphorescence were For the formation of (227) at 77 K the triplet of (226) has to absorb a second photon['491. (228) with ~is-chromophores~'~~1 undergoes cyclobutene opening without complications[l5'I.…”