Mechanical analog

Bromine reacts with alkanes by a free radical chain mechanism analogous to that of chlorine There is an important difference between chlorination and brommation how ever Brommation is highly selective for substitution of tertiary hydrogens The spread m reactivity among pnmary secondary and tertiary hydrogens is greater than 10 ... 

N Bromosuccimmide provides a low concentration of molecular bromine which reacts with alkenes by a mechanism analogous to that of other free radical halogenations... 

Polymerization of styrene is carried out under free radical conditions often with benzoyl peroxide as the initiator Figure 1111 illustrates a step m the growth of a poly styrene chain by a mechanism analogous to that of the polymerization of ethylene (Sec tion 6 21)... 

In organisms which produce cephalosporin and cephamycins, the configuration of the O -aminoadipyl side chain of (30) is D, while penicillin producers yield the l isomer. The exact point at which the configuration is inverted is unknown. Subsequent steps in cephalosporin biosynthesis are believed to involve ring expansion to deacetoxycephalosporin C (31), which may proceed by a mechanism analogous to the chemical pathway (see Section 5.10.4.2), followed by hydroxylation and acetylation at C-3 to produce cephalosporin C (32). 

Iodine azide, on the other hand, forms pure adducts with A -, A - and A -steroids by a mechanism analogous to that proposed for iodine isocyanate additions. Reduction of such adducts can lead to aziridines. However, most reducing agents effect elimination of the elements of iodine azide from the /mwj -diaxial adducts of the A - and A -olefins rather than reduction of the azide function to the iodo amine. Thus, this sequence appears to be of little value for the synthesis of A-, B- or C-ring aziridines. It is worthy to note that based on experience with nonsteroidal systems the application of electrophilic reducing agents such as diborane or lithium aluminum hydride-aluminum chloride may yet prove effective for the desired reduction. Lithium aluminum hydride accomplishes aziridine formation from the A -adducts, Le., 16 -azido-17a-iodoandrostanes (97) in a one-step reaction. The scope of this addition has been considerably enhanced by the recent... 

Spontaneous perfluoroalkylatwn ofenamines occurs in the presence of fluor-inated perhalogenoalkanes [743, 744] This condensation is interpreted by a SET process (mechanism analogous to equation 57 with a neutral nucleophile in place of a charged nucleophilic reagent). Formation of chlorodifluoromethylcyclo... 

The total energy, for example, may be written as a sum of atomic energies, and these atomic energies are again almost constant for the same structural units in different molecules. The atomic basins are probably the closest quantum mechanical analogy to the chemical concepts of atoms within a molecule. 

The Dakin reaction proceeds by a mechanism analogous to that of the Baeyer-Villiger reaction. An aromatic aldehyde or ketone that is activated by a hydroxy group in the ortho or para position, e.g. salicylic aldehyde 12 (2-hydroxybenzaldehyde), reacts with hydroperoxides or alkaline hydrogen peroxide. Upon hydrolysis of the rearrangement product 13 a dihydroxybenzene, e.g. catechol 14, is obtained ... 

Reaction of 2-methylpropene with CH3OH in the presence of H2SO4 catalyst yields methyl tert-butyl ether, CP OQCHT, by a mechanism analogous to that of acid-catalyzed alkene hydration. Write the mechanism, using curved arrows for each step. 

Treatment of a thiol with a base, such as NaH, gives the corresponding thiolate ion (RS-), which undergoes reaction with a primary or secondary alkyl halide to give a sulfide. The reaction occurs by an Sn2 mechanism, analogous to the Williamson synthesis of ethers (Section 18.2). Thiolate anions are among... 

Steps 3-4 of Figure 29.2 Hydrolysis The second nucleophilic acyl substitution step hydrolyzes the acyl enzyme and gives the free fatty acid by a mechanism analogous to that of the first two steps. Water is deprotonated by histidine to give hydroxide ion, which adds to the enzyme-bound acyl group. The tetrahedral... 

One suggested mechanism is that the reaction may take place by a conjugate hydride-transfer mechanism, analogous to what occurs during alcohol oxidations with NAD+. Electrons on the enolate ion might expel a (3 hydride ion, which could add to the doubly bonded NS nitrogen on FAD. Protonation of the intermediate at N1 would give the product. 

Jacobsen developed a method employing (pybox)YbCl3 for TMSCN addition to meso-epoxides (Scheme 7.22) [46] with enantioselectivities as high as 92%. Unfortunately, the practical utility of this method is limited because low temperatures must be maintained for very long reaction times (up to seven days). This reaction displayed a second-order dependence on catalyst concentration and a positive nonlinear effect, suggesting a cooperative bimetallic mechanism analogous to that proposed for (salen)Cr-catalyzed ARO reactions (Scheme 7.5). 

Laboratory studies have generally focused on the diisopropyl, dicyclohexyl and di-t-butyl derivatives. These and the. s-butyl and 2-cthylhcxyl derivatives arc commercially available.189 The rates of decomposition of the peroxydicarbonates show significant dependence on the reaction medium and their concentration. This dependence is, however, less marked than for the diacyl peroxides (36) (see 3.3.1.1.4). Induced decomposition may involve a mechanism analogous to that described for diacyl peroxides. However, a more important mechanism for primary and secondary peroxydicarbonates involves abstraction of an cx-hydrogen (Scheme 3.31).190... 

The vinylsilanes (e.g. 40, 41) do not readily homopolymerize. Forsyth et al.Mj explored the mechanism of grafting these monomers using dodecane as a model for PE. Their work suggests that multiple monomer units are attached through a sequence of addition and intramolecular hydrogen atom transfer steps by a mechanism analogous to that shown in Scheme 7.33 on page 394. 

In a very recent development, Debuigne et at. of vinyl acetate at 30 °C mediated by Co"(acac)2 (121). They obtained predictable molecular weights up to Mn 100000 and dispersities < 1.3 and proposed a polymerization mechanism analogous to that shown in Scheme 9.27. The complex... 

Tedder400 proposed that dual mechanisms, analogous to those proposed for alkylation, may apply to acylation also. Thus substitution may occur via a free... 

The reaction proceeds by a radical chain mechanism analogous to that outlined in equations 38-40. The observed stereoselectivity in the above addition indicates that reaction between the intermediate vinyl radical, ArS02CH=CR, and PhSeS02Ar must... 

The anodic polymerization of aniline can occur by a radical cation coupling mechanism analogous to that shown in Scheme 1, with coupling occurring between the N of one molecule and the para-position of another (Structure 4)21,22 However, a variety of other mechanisms have also been proposed,21 and it is likely that their relative rates depend upon the conditions (solvent, potential, pH, etc.) employed. The links between monomers are therefore not exclusively between the N and para-position (head-to-tail coupling). Head-head (-N=N-) and tail-tail (para-para) coupling occur more often as the pH is increased.71... 

In summary, ANTX-A(S) uses the two-site attachment mechanism analogous to substrate and does not inhibit AChE in the manner of the reversible anticholinesterases. 

A detailed derivation of the photoionization differential cross-section expression, leading ultimately to the angular distribution in Eq. (4), is provided in Appendix A. This will help provide a detailed understanding of the photoelectron dynamics that determine the angular distribution parameters, as will be discussed in a subsequent section, but for now it may help develop the reader s appreciation of this phenomenon to provide a simple, if necessarily inexact, mechanical analogy. 

The absence of retardation by V(IV) rules out a mechanism analogous to that of Mn(III) oxidation. Mn(II) ions strongly catalyse reaction , altering the kinetics to those observed for the Mn(II)-catalysed oxidation of oxalic acid by V(V) (preceding sub-section) except that the [V(V)] dependence has a Michaelis-Menten, form rather than being first-order. E is reduced from 19.7 to 6.9 kcal.mole , and a similar mechanism is believed to operate. 

A mechanism analogous in many ways to that of the acid-catalyzed ring opening reaction was advanced for the reaction of the thiirane oxide with alkyl chloromethyl ethers S . The first step is the displacement of the chloride by the sulfoxy oxygen (equation 24). In view of the above mechanistic interpretation, it is quite surprising that the parent thiirane oxide (16a) was found to be protonated on sulfur and not at oxygen in FSOjH-SbFfi at — 78 °C, according to NMR studies s . 

Equation (2.23) is the quantum-mechanical analog of the classical definition of momentum, p = mv = m(Ax/At). This derivation also shows that the association in quantum mechanics of the operator (h/i)(d/dx) with the momentum is consistent with the correspondence principle. 

As noted in the previous section, spin is a purely quantum-mechanical concept there is no classical-mechanical analog. 

This result is equivalent to that derived in Section 5.2.3 for the mechanical analog (problem 11). Equation (72) can be written... 

All of the photocrosslinking described here begin with surface of the films. The photocrosslinking leading to the solid films under a nitrogen atmosphere would proceed by the mechanism analogous... 

In the presence of nucleophilic solvents, a racemization is observed too in less than one hour, in the presence or in the absence of hydroquinone, compound (12) is fully racemized in methanol44. A mechanism analogous to that proposed to rationalize the optical instability of triorganotin halides can be given here 44). 

S-Nitrostyrene adds to 2,3-dimethylbutadiene to produce similar products, probably by a mechanism analogous to that above<65) ... 

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