N-pentyl radical

For pentyl radical, internal H-atom transfers can occur regardless of whether further oxidation occurs. These unimolecular reactions can directly compete with oxidation steps and so have implications for low-temperature combustion. For instance, n-pentyl radical can quickly isomerize to iso-pentyl radical via 1,4-H atom transfer each of these radicals can undergo p-scission reactions to yield a new alkyl radical + alkene ... 

A 1,4 shift of this type was postulated by Duncan and Cvetanovid27 to explain some of their results on the reaction of CH2 with isobutene and butene-2. Previously, Gordon and McNesby56 demonstrated that intramolecular hydrogen abstraction occurs in the case of n-pentyl radicals ... 

The n-pentyl radical is the largest alkyl radical for which Arrhenius parameters have been determined for a gas-phase metathetical reaction. Problems with volatility of reactants and dimer products are considerable in studies involving radicals larger than C4. The few results available for n-pentyl are given in Table 21. but in fact for only the first of the four reactions listed was there an experimental determination the other three results were obtained from data for the reverse reactions and the equilibrium constants derived from thermodynamic data. The selection of the rate coefficient for the n-pentyl dimerization reaction, upon which to base the absolute data for the reaction... 

Perhaps most pertinent to this review, model compounds play an integral role in the development of detailed chemical kinetic mechanisms. For instance, w-propylperoxy," 1-butoxy radical," and n-pentyl" radical are, respectively, the simplest alkylperoxy radical, alkoxy radical, and alkyl radical capable of undergoing facile 1,5-H atom transfers (each via a favorable six-membered-ring transition state, as illustrated in Figure 2). Thus, these smaller systems are commonly used as models to investigate the comparable isomerizations possible in the larger radical, oxy radical, and peroxy radical species that are involved in FlC fuel combustion. 

Figure 2 The figure shows 1,5-H atom transfers in (from left) n-propylperoxy radical, 1-butoxy radical, and n-pentyl radical, used to investigate the corresponding isomerizations in larger alkylperoxy radicals, alkoxy radicals, and alkyl radicals, respectively.

In addition, Kozuka and Lewis measured the tritium isotope effect for the reaction between the n -hexyl, the 2-hexyl and the 2-methy 1-2-pentyl radicals with triphenyltin hydride and triphenyltin hydride-t see the last three entries in Table 11. The isotope effect of 2.55 found for the triphenyltin hydride-w-hexyl radical reaction was slightly smaller... 

For amidyl radicals carrying a 6-hydrogen in the alkyl chain (e.g., XVII or N-pentyl, N-butyl, N-phenylbutyl analogues) intramolecular abstraction of the 6-hydrogen as in XVII and the collapse to 6-nitroso compound XVIII are very facile and occur preferentially within the radical pair (vide infra) over other... 

The alkyl radical ionization potentials needed were calculated by the pseudo-ir-orbital method.20 It was found21 that these radical ionization potentials converge to a constant value at the pentyl radicals. For various structures the values were as follows n-pentyl, 8.60 e.v. sec-pentyl, 7.81 e.v. iso-pentyl, 8.48 e.v. teri-pentyl, 7.19 e.v. (see ref. 21 for details of these calculations). The molecular ionization potentials also converge to a constant value at about ten carbons. Whenever these constant values are reached the heats of formation of the ions in Table II vary only with the heat of formation of the associated alkane, and therefore decrease by 5 kcal. mole-1 for each successive carbon atom. 

H-transfer is always ca. 10 faster than 1 4 H-transfer at 600 °K (see Table 3), so it will predominate when the molecular structure of the fuel permits. Simple estimation of the relative concentrations of the hydroperoxyalkyl radicals derived from propane, n-butane and n-pentane illustrates this. Thus, if the relative frequency of attack by OH at primary, secondary and tertiary C—H bond is taken as 2 3 5 [102], then the relative concentrations of propyl, butyl and pentyl radicals may be obtained. The equilibrium constant for reaction (3)... 

Maccoll et have pointed out that along the series of primary bromides (n-propyl, n-butyl, n-pentyl, n-hexyl) the chain component of the overall thermal decomposition undergoes a steady decrease relative to the unimolecular component of the decomposition. This has been attributed to the increased probability of formation of -radicals with increase in the length of the carbon chain in the molecule. The decomposition of secondary monobromides is mainly unimolecular with only a slight radical-chain component. Tertiary monobromides decompose uni-molecularly. 

ESR work (16) shows that 2-pentyl radicals (CH3—CH2—CH2— CH—CH3) are trapped in solid n-pentane irradiated at 77 °K. Careful examination of the ESR signal indicates that other radicals are produced with much lower yields than 2-pentyl radicals. The measurements do not allow the identification of these minor products. When the temperature of the sample is raised, the ESR signal disappears just below the melting point of the n-pentane matrix. 

The disproportionation-combination ratio is temperature dependent. For sec-butyl radicals, this ratio is 2.3 at 375°K. (11) and 11 at 90°K. (10). Adopting the same values for pentyl radicals we calculate a ratio of 7.5 at 143°K. (melting point of n-pentane) at which recombination occurs. 

Dimers and trimers are produced by radiolysis of n-pentane in the solid phase. The yields of the various dimers have been measured. These yields suggest a much higher production of 1-pentyl radicals than does the ESR study of these transformations. Occurrence of non-radical processes in dimer production would account for this discrepancy. Trimer production strongly suggests the occurrence of ion-molecule reactions. These reactions would also yield dimers. Dimers would thus be formed by ionic and by radical processes. 

With this information in hand, it seemed reasonable to attempt to use force field methods to model the transition states of more complex, chiral systems. To that end, transition state.s for the delivery of hydrogen atom from stannanes 69 71 derived from cholic acid to the 2.2,.3-trimethy 1-3-pentyl radical 72 (which was chosen as the prototypical prochiral alkyl radical) were modeled in a similar manner to that published for intramolecular free-radical addition reactions (Beckwith-Schicsscr model) and that for intramolecular homolytic substitution at selenium [32]. The array of reacting centers in each transition state 73 75 was fixed at the geometry of the transition state determined by ah initio (MP2/DZP) molecular orbital calculations for the attack of methyl radical at trimethyltin hydride (viz. rsn-n = 1 Si A rc-H = i -69 A 6 sn-H-C = 180°) [33]. The remainder of each structure 73-75 was optimized using molecular mechanics (MM2) in the usual way. In all, three transition state conformations were considered for each mode of attack (re or ) in structures 73-75 (Scheme 14). In general, the force field method described overestimates experimentally determined enantioseleclivities (Scheme 15), and the development of a flexible model is now being considered [33]. 

A study of the reactions of perfluoroalkyl radicals [generated electrochemically from the acids RfCOsH (Rf = CFs, C2F5, n-CaF , or n-CvFis)] with the olefins CH2 CHR (R = Pr , Bu", n-pentyl, CN, COaMe, or CHa-COaMe) has been undertaken in each case the major product is of the type RfCH2 CHR-CHR CHaRr (22.5—50%), and in the majority of the reactions the compounds RpCHa CHaR, RfCH CHR, and RrCHa-CHRRF are also formed. 

Table 5 gives the propagation reactions (not including metatheses) of the lumped primary mechanism of the oxidation of n-pentane. It must be noted that this scheme only includes 4 free radicals instead of 24 for the detailed mechanism 3 pentyl radicals, 3 peroxy radicals, 9 hydroperoxypentyl radicals and 9 hydroperoxypentyl-peroxy radicals the dihydroperoxypentyl radicals have not been considered. 

The mechanism of reaction of a variety of triphenylphosphinealkyl-gold(i) complexes, and of triphenylphosphinetrimethylgold(iii), with mercury(n) chloride in a variety of solvents is St2. But when the alkyl group is cyano(ethoxycarbonyl)pentyl then the mechanism is dissociative. Decomposition of triphenylphosphine-n-butylcopper must involve initial formation of butene and a transient copper hydride rather than of n-butyl radicals, since no octane can be detected in the ultimate products. ... 

Amyl a-m3l [L amylum-l-E -yl] (1850) n. The radical C5H11-, also known as pentyl. The amyl radical occurs in six isomeric forms, and the term amyl usually refers to any mixture of the isomers. 

Dideoxynebularine (2 ,3 -dideoxypurine nucleoside, ddPN) 1 was one of a number of C-6 modified purine dideoxynucleosides synthesized in our laboratory (Scheme 2). It was designed to be a prodrug of ddl and was synthesized from 5 -protected ddA by reductive deamination using a procedure previously developed by us, followed by deprotection. Compound 1 was found to be inactive against the cytopathic effect of HIV-l and HIV-2 in MT-4 cells. It was not toxic to MT-4 cells at 200 jiM. It was not a substrate for xanthine oxidase. In contrast, C-6 substituted purine dideoxynucleosides that are substrates for mammalian ADA, show anti-HIV activity [e.g., 6-iodo ddPN, 2, synthesized from 5 -protected ddA by radical deamination/halogenation (n-pentyl nitrite, CH,L, CHjCN, A), followed by deprotection]. 

Atmospheric destruction of di-n-pentyl ether will be quite rapid, with loss occurring mainly via reaction with OH. Reactions with NO3 and Cl-atoms may also play a minor role. For daytime [OH] 2.5 x 10° molecule cm", a lifetime of 3 h is determined. The main site for OH reaction will be at the CH2 groups located adjacent to the ether linkage expected products include n-pentyl formate and HOCH2CH2CH2CHO (the end product of 1-butyl radical oxidation) ... 

Combining ife(OH n-C5Hn0C(0)CH3) = 7.39 x lO- cm molecule- at 298 K with a diurnal average of [OH] 1.0 x 10 molecule cm gives an estimate of about 1.5 days for the atmospheric lifetime with respect to reaction with OH radicals. Reaction with OH radicals dominates the atmospheric fate of n-pentyl acetate. Using the structure-activity relationship method outlined by Kwok and Atkinson (1995) with F(—OC(O)H) = 0.6 and k(—OC(O)H) = 0.9 x 10 cm molecule" s , it can be estimated that attack of OH radicals on n-pentyl acetate occurs 98% at the n-pentyl group, and 2% at the acetate group. 

R = n-pentyl Free-radical thermal, RT, Et20, vinyl comonomer, (b) AIBN, projrellane comonomer Copolymerization observed (a) [112[ (b) [111]... 

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