Rate Constants For Rearrangement Research Articles

Interfacial dynamic adsorption behaviour of the bovine alpha- Lactalbumin at the oil-water interface: Evaluating the role of glycyrrhizin

The contribution of glycyrrhizin (Gy) on the interfacial dynamic adsorption behaviour of the adsorbed layer formed by the bovine alpha-Lactalbumin (α-La) at the oil-water interface were investigated using the interfacial viscoelasticity and quartz crystal microbalance with dissipation (QCM-D) techniques. Compared to the individual α-La, Gy could decrease the interfacial tension, effectively enhancing their adsorption processing. The adsorption kinetic results revealed the diffusion rate of the α-La reduced at 0.5–2.0 mM Gy and its rate constant of rearrangement increased except for 2.0 mM. Also, Gy reduced the viscoelastic modulus including the elastic and viscous modulus of the adsorbed film formed by the α-La. Additionally, more adsorbed mass on the oil-water interface was observed in the α-La/Gy complex according to the QCM-D results, which can improve the stability at the oil-water interface. These results are expected to provide basic interfacial adsorption information for the film formed by multi-component.

Driving to a Better Understanding of Acyl Glucuronide Transformations Using NMR and Molecular Modeling.

Acyl glucuronide (AG) metabolites of carboxylic acid-containing drugs and products of their transformations have long been implicated in drug-induced liver injury (DILI). To inform on the DILI risk arising from AG reactive intermediates, a comprehensive mechanistic study of enzyme-independent AG rearrangements using nuclear magnetic resonance (NMR) and density functional theory (DFT) was undertaken. NMR spectroscopy was utilized for structure elucidation and kinetics measurements of nine rearrangement and hydrolysis products of 1β-O-acyl glucuronide of ibufenac. To extract rate constants of rearrangement, mutarotation, and hydrolysis from kinetic data, 11 different kinetic models were examined. Model selection and estimated rate constant verification were supported by measurements of H/D kinetic isotope effects. DFT calculations of ground and transition states supported the proposed kinetic mechanisms and helped to explain the unusually fast intramolecular transacylation rates found for some of the intermediates. The findings of the current study reinforce the notion that the short half-life of parent AG and slow hydrolysis rates of AG rearrangement products are the two key factors that can influence the in vivo toxicity of AGs.

Bulk and interfacial behaviour of caseinoglycomacropeptide (GMP)

Caseinoglycomacropeptide (GMP) is a hydrophilic glycopeptide released from milk κ-casein by chymosin hydrolysis during cheese making. GMP is thought to be a potential ingredient for specific dietary applications with several health benefits. In this study GMP was characterized at the air–water interface and its behaviour was related with the self-assembly of GMP in solution as affected by pH. This GMP self-assembly was investigated by dynamic light scattering and the interfacial properties were determined by tensiometry and surface dilatational measurements at pH 4, 5 and 7. At pH 5 GMP exhibited higher surface pressure at equilibrium than at pH 7. At pH 4 the behaviour was more complex due to self-assembly close to GMP pI. Dynamic measurement showed that the adsorption/penetration rate constant ( K ads) is facilitated at higher GMP bulk concentrations, while the rate constant of rearrangement ( K r) decreased at higher GMP concentrations which could be attributed to the existence of a steric restriction due to the higher GMP load at the interface. K r was higher at pH 5 because of lower electrostatic interactions close to the pI. The viscoelastic properties showed a complex behaviour due to the existence of protein–protein interactions depending on the GMP concentration, on the pH of the bulk and on the rates of diffusion, adsorption and rearrangement of GMP at the air–water interface.

Phosphaalkenes as Long-Lived Phosphorus Cluster Surface Functional Groups: Intramolecular P═C Addition to a Niobium-Supported P7 Cage

The diniobium octaphosphorus complex (P8)[Nb(OC[(2)Ad]Mes)3]2 (1) (Ad = adamantylidene, Mes = 2,4,6-Me3C6H2) contains a reactive niobium phosphinidene moiety that can be exploited for metathetical scission of the NbP bond. When 1 is treated with aryl ketones, loss of ONb(OC[(2)Ad]Mes)3(OEt2) (2) is observed along with concomitant formation of the corresponding phosphaalkene (RC6H4)2CPP7Nb(OC[(2)Ad]Mes)3 (3-R). Complexes 3-R rearrange to incorporate the (RC6H4)2CP unit into the phosphorus cage, thereby generating a saturated organo-phosphorus cluster complexed to the niobium tris-enolate platform, (RC6H4)2CP8Nb(OC[(2)Ad]Mes)3 (4-R). The structure of one such rearranged cluster 4-H, as determined by X-ray crystallography, is briefly discussed. An Eyring analysis of the first-order rearrangement of 3-H to 4-H gives activation parameters of DeltaH(double dagger) = 16.7 kcal/mol and DeltaS(double dagger) = -20.4 eu. A Hammett analysis of the phosphaalkene rearrangement, 3-R to 4-R, with substitution varying at the para positions of the aryl rings, reveals a linear relationship between the sigma values and the rearrangement rate constants. A concerted, asynchronous mechanism for the least-motion rearrangement of 3-H to 4-H is presented. When 1 is treated with alkyl ketones, similar loss of 2 and formation of the corresponding phosphaalkene is observed; however, the phosphaalkene complexes have considerably greater stability and are readily isolated.

DFT Evidence for a Stepwise Mechanism in the O-Neophyl Rearrangement of 1,1-Diarylalkoxyl Radicals

Hybrid DFT calculations of the potential energy surface (PES) relative to the O-neophyl rearrangement of a series of ring-substituted 1,1-diarylalkoxyl radicals have been carried out at the UB3LYP/6-31G(d) level of theory. On the basis of the computational data, the rearrangement can be described as a consecutive reaction of the type a <--/--> b --> c (see above graphic), and the steady-state approximation could be applied in all cases to the intermediate b. The first-order rearrangement rate constants [kobs = k1k2/(k-1 + k2)] were thus obtained from the computed activation free-energies and were compared with the experimental rate constants measured previously in MeCN solution by laser flash photolysis. An excellent agreement is observed along the two series, which strongly supports the hypothesis that the O-neophyl rearrangement of 1,1-diarylalkoxyl radicals proceeds through the formation of the reactive 1-oxaspiro [2,5]octadienyl radical intermediate. This is in contrast to previous hypotheses that involve either a long-lived intermediate or the absence of this intermediate along the reaction path. The calculated rearrangement free-energies decrease upon going from the methoxy-substituted radical (Delta G degrees = -16.4 kcal x mol-1) to the nitro-substituted one (Delta G degrees = -21.8 kcal x mol-1), which follows a trend that is similar to the one observed for the CAr-O bond dissociation enthalpies (BDEs) of ring-substituted anisoles. This evidence indicates that in the O-neophyl rearrangement the effect of ring substituents on the strength of the newly formed CAr-O bond plays an important role.

The Effect of Ring Substitution on theO-Neophyl Rearrangement of 1,1-Diarylalkoxyl Radicals. A Product and Time-Resolved Kinetic Study

[reaction: see text] A product and time-resolved kinetic study of the effect of ring substitution on the reactivity of 1,1-diarylalkoxyl radicals has been carried out. The radicals undergo an O-neophyl shift to give the isomeric 1-aryl-1-aryloxyalkyl radicals from which the corresponding aromatic ketones are formed. The rearrangement rate constants are influenced by ring substitution, increasing in the presence of electron-withdrawing substituents and decreasing in the presence of electron-donating ones. From the results of product and kinetic studies, the following migratory aptitudes have been obtained: 4-trifluoromethylphenyl > phenyl approximately = 4-methylphenyl > 4-methoxyphenyl. Excellent Hammett-type correlations between the sigma+ substituent constants and both the visible absorption band maxima and the rearrangement rate constants have been obtained. The experimental results indicate that the rearrangement is governed by electronic effects in the starting 1,1-diarylalkoxyl radicals, whereas the stability of the rearranged carbon-centered radical plays a minor role, in line with a reactant-like transition state, strongly supporting the hypothesis that the O-neophyl rearrangement of 1,1-diarylalkoxyl radicals proceeds through a concerted mechanism.

Radical clocks and electron transfer. Comparison of crown ether effects on the reactivity of potassium and magnesium towards 1-bromo-2-(3-butenyl)benzene. The incidence of homogeneous versus heterogeneous electron transfer on selectivity

The reaction of the title precursor of the aryl radical clock 1-bromo-2-(3-butenyl)benzene, 1Br, towards potassium and magnesium in THF was studied in the presence and absence of various additives, at ambient and low temperatures. The additives were cis-dicyclohexano-18-crown-6 or tert-butyl alcohol; the first one to render soluble potassium by forming its alkalide, the second to distinguish carbanionic from radical cyclization. The addition of 1Br to a THF stirred suspension of potassium pieces yields remarkably low amounts of products resulting from radical cyclization, in contrast to the amounts reported by Bunnett and Beckwith's group for the reaction in 67% ammonia–33% tert-butyl alcohol medium. The amount of cyclized products obtained with potassium pieces in THF is in the same range as that observed in the reaction of magnesium with 1Br in THF. This similarity allows us to discard the earlier triad hypothesis that we proposed to account for the unexpectedly low amounts of cyclized products of aryl halides radical clocks in Grignard reagent formation. The addition of crown ethers to the THF reaction medium induces contrasting effects for potassium and magnesium. A distinctive increase in the radical cyclization is observed for potassium, whereas the addition of crown inhibits the formation of Grignard reagent more efficiently when the solvent is diethyl ether than when it is THF. The observed effects are explained by putting in perspective the metal reactive dissolution with elementary steps occurring in the vicinity of a cathode. The reaction of potassium pieces or magnesium turnings is comparable to the heterogeneous electron transfer occurring at a cathode whereas the reaction of potassium in the presence of crown ether is comparable to homogeneous conditions of electron transfer obtained in redox catalysis. A discussion of the dianion hypothesis for the Grignard reaction of aryl halides is provided and the importance of considering the reactivity of reactive metal dissolution (or organic corrosion) in the framework of recent progress made in the modelling of electrode reactivity is emphasized. This paper shows that caution should be taken when radical clocks are used to study reactions at the metal–solution interface. More specifically, the non-observation of rearranged products from the radical clock (even for the very rapid ones) under these conditions does not necessary imply that there is no radical intermediate along the dominant reaction channel. This pattern of reactivity strongly contrasts with that usually observed when radical clocks are used in homogeneous media. The leading parameters in the rearranged/unrearranged products ratio seem to be the time that the reactive species (radical anions) created by the first electron transfer spend in the close vicinity of this surface, the rate constant of rearrangement of the radical formed by the cleavage of the radical anion and the redox properties of this radical. Copyright © 2005 John Wiley & Sons, Ltd.

Phenyl-bridging in the 2-phenylethyl radical. A molecular orbital study.

Density functional theory at the UB3PW91/6-31G(d.p) level on the open and bridged forms of the 2-phenylethyl radical are reported here together with activation energies and calculated rate constants for rearrangement of the bridged to the open radical. In addition, the effect of substituents on the aryl ring upon the relative energies, activation energies, and rate constants for rearrangement from the bridged to open forms are presented. Para-substituents include CH3, CF3.CN, CHO.OH, SH, O-, S-, and NO. The parent bridged radical is found to be 10.1 kcal/mol higher in enthalpy than the open form. The activation energy for conversion of the bridged to open radical is 3.96 kcal/mol. Para-substitution by CN or CHO significantly lowers the difference in energy between the species, while substitution by NO renders the bridged form more stable. Para-substitution by CN or CHO coupled with substitution with CN in the ortho-positions makes the open and bridged radical approximately equivalent in energy.

X-ray crystal comparisons and rates of conversion between RS/ SR and RR/ SS-[Ni( n-PrAO) 2–H] +

The planar bis-[ N-alkyl-α-amineoxime] complexes of nickel(II) are shown to be relatively stable in either the meso( RS/ SR) or dl( RR/ SS) form by 1H NMR and X-ray analysis. They can be isolated, quantitatively separated and analyzed for by HPLC. As bromide salts they crystallize separately having different crystal morphology and color. The X-ray crystal structures have different unit cell symmetry: meso, orthorhombic, Aba2 while the dl isomer is monoclinic, P2 1/ c. The unit cells contain similar monomeric nickel(II) cations, bromide ion and a non-coordinated water molecule. They differ only in the geometric arrangement around the asymmetric nitrogens. In solution, the isomers slowly convert to equilibrium mixtures ( t 1/2≈1–5000 min at 0°), with the rate and K eq being highly dependent on the solvent and the solution acidity. The equilibrium constant, K eq=[ meso]/[ dl], measured in various solvents, combined with the observed first-order rate constants for rearrangement give k f and k r values. These are compared under different conditions and possible mechanisms for racemization are discussed. Both the rates of interconversion and the equilibrium ratios are very sensitive to solvent composition.

A laser flash photolysis and quantum chemical study of the fluorinated derivatives of singlet phenylnitrene.

Laser flash photolysis (LFP, Nd:YAG laser, 35 ps, 266 nm, 10 mJ or KrF excimer laser, 10 ns, 249 nm, 50 mJ) of 2-fluoro, 4-fluoro, 3,5-difluoro, 2,6-difluoro, and 2,3,4,5,6-pentafluorophenyl azides produces the corresponding singlet nitrenes. The singlet nitrenes were detected by transient absorption spectroscopy, and their spectra are characterized by sharp absorption bands with maxima in the range of 300-365 nm. The kinetics of their decay were analyzed as a function of temperature to yield observed decay rate constants, k(OBS). The observed rate constant in inert solvents is the sum of k(R) + k(ISC) where k(R) is the absolute rate constant of rearrangement of singlet nitrene to an azirine and k(ISC) is the absolute rate constant of nitrene intersystem crossing (ISC). Values of k(R) and k(ISC) were deduced after assuming that k(ISC) is independent of temperature. Barriers to cyclization of 4-fluoro-, 3,5-difluoro-, 2-fluoro-, 2,6-difluoro-, and 2,3,4,5,6-pentafluorophenylnitrene in inert solvents are 5.3 +/- 0.3, 5.5 +/- 0.3, 6.7 +/- 0.3, 8.0 +/- 1.5, and 8.8 +/- 0.4 kcal/mol, respectively. The barrier to cyclization of parent singlet phenylnitrene is 5.6 +/- 0.3 kcal/mol. All of these values are in good quantitative agreement with CASPT2 calculations of the relative barrier heights for the conversion of fluoro-substituted singlet aryl nitrenes to benzazirines (Karney, W. L. and Borden, W. T. J. Am. Chem. Soc. 1997, 119, 3347). A single ortho-fluorine substituent exerts a small but significant bystander effect on remote cyclization that is not steric in origin. The influence of two ortho-fluorine substituents on the cyclization is pronounced. In the case of the singlet 2-fluorophenylnitrene system, evidence is presented that the benzazirine is an intermediate and that the corresponding singlet nitrene and benzazirine interconvert. Ab initio calculations at different levels of theory on a series of benzazirines, their isomeric ketenimines, and the transition states converting the benzazirines to ketenimines were performed. The computational results are in good qualitative and quantitative agreement with the experimental findings.

Mechanistic insights into C–H activation from radical clock chemistry: oxidation of substituted methylcyclopropanes catalyzed by soluble methane monooxygenase from Methylosinus trichosporium OB3b

The soluble methane monooxygenase (MMO) system isolated from Methylosinus trichosporium OB3b catalyzes the adventitious oxidation of alkyl substituted methylcyclopropanes. If the chemical mechanism of C–H activation by MMO involves formation of a radical or carbocation intermediate at the methyl C–H of these ‘radical clock’ substrates, then cyclopropyl ring opened alcohols may appear in the product mixture due to rearrangement of the intermediate. The lifetime of radical intermediates can be determined from known rearrangement rate constants, k r. Rearrangement was observed during the oxidation of 1,1,2,2-tetramethylcyclopropane ( k r=1.7–17.5×10 8 s −1, 30°C) but not for cis- or trans-1,2-dimethylcyclopropane ( k r=1.2–6.4×10 8 s −1, 30°C) or the very fast radical clock, trans-2-phenylmethylcyclopropane ( k r=3.4×10 11 s −1, 30°C). The results show that the occurrence of rearranged products fails to correlate with either the chemical nature of the C–H bond being broken, which is very similar for all of the methylcyclopropanes studied here, or the magnitude of the radical k r value. This study suggests that the steric properties of the substrate play an important role in determining the outcome of the reaction. Substrates with bulky substituents near the C–H bond that is attacked appear to yield intermediates with sufficient lifetimes to rearrange. In contrast, substrates with less steric bulk are postulated to be able to approach the reactive oxygen species in the MMO active site more closely so that intermediates are either rapidly quenched or undergo subsequent interaction with the dinuclear iron cluster of MMO that prevents rearrangement.

Laser Flash Photolysis Study of Methyl Derivatives of Phenyl Azide

Laser flash photolysis (Nd:YAG, 35 ps, 266 nm, 10 mJ; KrF excimer, 249 nm, 12 ns, 70 mJ; XeCl excimer, 308 nm, 17 ns, 50 mJ) of methyl substituted phenyl azides produces the corresponding singlet nitrenes. The singlet nitrenes were detected directly, and their decay was analyzed to yield the observed rate constant kOBS. The observed rate constant is the sum of kR + kISC where kR is the absolute rate constant of rearrangement to an azirine and kISC is the absolute rate constant of intersystem crossing. Values of kOBS were measured as a function of temperature and dissected assuming that kISC is temperature-independent. It was shown that kISC is independent of temperature for 2,6-dimethyl- and 2,4,6-trimethylphenyl singlet nitrenes. The barriers to rearrangement of singlet phenylnitrene, p-methylphenylnitrene, o-methylphenylnitrene, 2,6-dimethylphenylnitrene, and 2,4,6-trimethylphenylnitrene in hydrocarbon solvents are found to be 5.6, 5.8, 5.3, 7.0, and 7.3 ± 0.4 kcal/mol, respectively. The data demonstrate that two ortho methyl substituents retard cyclization but that a single ortho or para substituent does not. It is concluded that the rate of retardation provided by the methyl groups has a steric origin, as predicted by Karney and Borden (J. Am. Chem. Soc. 1997, 119, 3347). These authors predict that ortho methylation raises the barrier to cyclization by 1−2 kcal/mol, in excellent agreement with our results. Our results are also consistent with the work of Sundberg et al. (J. Am. Chem. Soc. 1972, 94, 513), which demonstrated that singlet 2-methylphenylnitrene cyclizes away from the ortho methyl substituent. Methyl substitution is found to increase the absolute rate constant of intersystem crossing.

Laser Flash Photolysis and Computational Study of Singlet Phenylnitrene

Laser flash photolysis (LFP, Nd:YAG laser, 35 ps, 266 nm, 10 mJ) of phenyl azide (PA) releases open-shell singlet phenylnitrene (1PN). 1PN has a sharp absorption band at 350 nm and a very weak absorption band at 540 nm. These bands are assigned as nz−ny and a mixture of 52% π−nx and 28% nx−π* transitions, respectively, on the basis of CASSCF and CASPT2 calculations. A CASPT2 calculation of the spectrum of triplet phenylnitrene (3PN) is in very good agreement with the experimental spectrum. A sharp absorption band of 3PN at 308 nm and a broad, structured band at 370 nm are assigned as nz−ny and π−π transitions on the basis of CASSCF and CASPT2 calculations. The low intensity, long wavelength band of 3PN tailing to 500 nm is assigned as a mixture of π−nx, nx−π* transitions. The decay of 1PN in pentane was measured as a function of temperature to obtain observed rate constants of disappearance, kobs. The rate constant kobs is equal to kR + kISC, where kR is the absolute rate constant of rearrangement of 1PN ...

Theoretical model for an alternate mechanism for the cytochrome P-450 hydroxylation of quadricyclane

During the past decade the mechanism of enzymatic hydroxylation of saturated hydrocarbons has come under increased scrutiny.’ The widely accepted mechanism for the catalytic cycle for cytochrome P-450 monooxygenase hydroxylation of alkanes is thought to involve the recombination of an iron-bound hydroxyl radical with a carbon-centered free radical in a process termed “oxygen rebound”.2 Another related area of chemistry that has developed simultaneously is the use of “radical clock’ substrates to estimate the magnitude of the rate constant for the oxygen rebound step ( k o ~ ) . If alkane hydroxylation is initiated by hydrogen abstraction, then the free-radical intermediate may be hydroxylated directly (&) or it may undergo rearrangement (k,) and subsequent recombination to afford a rearranged alcohol as exemplified for the P-450 hydroxylation of bicyclo[2.1 .O]pentane (Scheme 1). Ortiz de Montellano and reported a 7:l ratio of unrearranged (4) to rearranged (5) alcohols, implying that the oxygen rebound step is about seven times faster than the ring-opening of bicyclo[2.1 .O]pent2-yl radical (2) in Scheme 1. We predict a classical activation barrier for rearrangement of 2 to cyclopenten-4-yl radical 3 of 6.8 kcdmol (AG*298 = 6.23 kcaVmol) at the PMP4 level and a rate constant at 25 “C of k, = 1.7 x lo8 s ’ . ~ A recent estimate of the rate constant for radical recombination to form unrearranged alcohol 4 is OH = 2.2 x 1O’O During the past several years the kinetic scale for these very rapid radical reactions has approached the theoretical limit for the frequency factor kTlh = Measured unimolecular rate constants for rearrangement of aryl-substituted cyclopropylcarbinyl radical of 5 x 10’’ s-’ have been r e p ~ r t e d ~ ~ . ~ requiring an estimated rebound rate constant for enzymatic hydroxylation8 with methane monooxygenase of kOH > 1OI3 SKI.

Antihydrogen at sub-Kelvin temperatures

We discuss the behavior of magnetically trapped antihydrogen ( $$\bar H$$ ) at temperatures relevant for gravity and spectroscopy experiments (well below 1 K) and the possibilities of attaining these temperatures. Two possible options are considered. In the discussion of the first one, i.e. $$\bar H$$ as admixture in cold H gas, we develop the quantum-mechanical theory of $$\bar H$$ -H (and also $$\bar p$$ -H) elastic and rearrangement collisions at ultra-low (sub-Kelvin) energies, when s-wave scattering in the incoming channel dominates. The rate constant of rearrangement leading to $$\bar H$$ decay turns out to be large, which makes the possibilities for $$\bar H$$ collisional cooling in H gas and $$\bar H$$ -H coexistence rather limited. As we show, the most promising is the other option, i.e. $$\bar H$$ atoms in the collisionless regime. For this regime the possibility of one-dimensional adiabatic cooling of $$\bar H$$ is demonstrated by using the example of the Ioffe trap. This phenomenon, interesting from the fundamental point of view, offers the opportunity to cool $$\bar H$$ below 1 mK.

Effects of substituents in acid-catalyzed Claisen amino rearrangement

A series of 4-R2-N-R1-N-(1-methyl-2-butenyl)- and 4-R2-N-R1-2-(1-methyl-2-butenyl)-anilines was synthesized. The rate constants of rearrangement and elimination of the hydrochlorides of the 4-R2-N-R1-N-(-1methyl-2-butenyl)anilines in nitrobenzene were measured at 110 and 130°C. The correlation equations which describe the effect of the nature of the substituents on the reactivity of the substrate in these reactions and the selectivity of their occurrence were established. A mechanism of the processes was proposed.

Interaction of polyfluoroaromatic compounds with o-aminophenol. The Smiles rearrangement in the polyfluoroaromatic series

The reactions of polyfluoroaromatic compounds containing an electron-attracting substituent other than fluorine in the aromatic ring with o-aminophenol proceed at the amino or hydroxy group and lead to the corresponding hydroxydiarylamines (in neutral media) or aminodiaryl ethers (in alkaline media). The latter compounds, unlike 2,3,4,5,6-pentafluoro- 2'-aminodiphenyl ether, are transformed in dimethylformamide (DMFA) to isomeric polyfluoro-2-hydroxydiarylamines (the Smiles rearrangement). The increased electron-attracting capacity of substituent leads to the decreased activation energy and increased rearrangement rate constants.

A homopropargyl radical rearrangement. Kinetics of the rearrangement of the 2,2,5,5,-tetramethyl-3-hexyn-1-yl radical

The rate constants for rearrangement of the 2,2,5,5-tetramethyl-3-hexyn-1-yl radical to the 2,6,6-trimethyl-4-heptyn-2-yl radical have been measured from 45 to 88 °C by kinetic epr spectroscopy. The temperature dependence can be represented by[Formula: see text]where θ = 2.3RT kcal mol−1. This rearrangement, which must involve an intermediate vinyl radical of the methylenecyclopropane type, is much slower than analogous rearrangement of homoallyl radicals but comparable in rate to rearrangement of homobenzyl (neophyl) radicals.

Determination of rate constants for rearrangement of ?-carbalkoxyalkyl radicals by the EPR method employing spin traps

The rate constants for the rearrangement ofω-carbalkoxyalkyl radicals, with 1,6-, 1,5-,and 1,4-migration of the hydrogen atom, were determined.