Reactions, spontaneous, mechanical

R and S configurations, 12ff Racemization, 69, 82, 124 Radicals, 31, 61, 222 Raney nickel, 295 Rate-controlled reaction, 150 Reaction mechanism, 31,41 Reaction rate, 39, 48 Reaction, spontaneity of, 36 Reactions, addition-elimination, 2 ljf Reactions, aromatic, 99ff Reactivity-selectivity principle, 59, 211 Redox, 33... 

In general, K-region arene oxides behave rather like aliphatic epoxides and thus readily undergo hydration reactions, whereas benzene oxides and non-K-region arene oxides form dihydrodiols much more reluctantly. Kinetic studies of the mechanism of solvolysis of phenanthrene 9,10-oxide 2 have been carried out in several laboratories.Below pH 7 the hydrolysis reaction was acid-catalyzed and the products included the trans- and c/s-9,10-dihydrodiols along with a preponderance of 9-phenanthrol, while above pH 7 the reaction proceeded via the spontaneous mechanism ( o) mainly the frans-dihydrodiol. 

By introduction of reaction-difiusion mechanism, self-organization, and self-regulation perceptions in the oscillating reactions, its applications have grown substantially in recent years. The reaction-difiusion mechanism is found to be veiy usual in diverse kinds of natural phenomenon that employed to assemble and fabricate the stmctures on the length scales. On the other hand, self-organization is treated as a fantastic phenomenon by which a spontaneous dissipative pattern could be possible by input of energy and matter in non-equilibrium conditions. 

The formation of polyaniline (PANI) between the layers of montmorillonite (Fig. 16) is an illustrative example of the in situ polymerization procedure. As already posmlated in the 1960s by several authors, montmorillonite-adsorbed aniline spontaneously oxidizes and polymerizes by the catalytic action of Cu ions (145,146) or by atmospheric oxygen (147,148). Evidence of such reactions and mechanisms were first advanced by Cloos and coworkers (149,150) 20 years... 

The conversion of dihydroartemisinic acid to artemisinin is believed to be a ntMienzymatic spontaneous photooxidation or autoxidation reaction. The mechanism of this complex transformation is shown to involve four steps first, initial reaction of the C11-C12 double bond of dihydroartemisinic acid with single molecular oxygen second is the Hock cleavage of the resulting tertiary allylic... 

In contrast, cyclic carbonate with an exo-methylene substituent in the ring polymerizes via an SnI mechanism. Such a monomer can undergo ring-opening reaction spontaneously to produce a linear product with allyl cation that will be attacked by the carbonyl oxygen atom of the next monomer molecule according to the SnI mechanism (Scheme 27). It should be noticed that allyl carbocation is stabilized by an electron delocalization. 

The S y.jl mechanism can be an excellent route to isoquinoHnes rings and derivatives by reaction of o-iodobenzylamines with ketone enolate ions under irradiation.The substitution products formed in their irradiated reactions spontaneously cyclize to give a non-isolable intermediate which affords iso-quinolines by Pd/C dehydrogenation (Eq. (47.35a)) or tetrahydroisoquinohnes by reduction with NaBH4 in approximately 100% yields (Eq. (47.35b)... 

Enzymes act by lowering the overall activation energy of a reaction sequence by involving a series of intermediates, or a mechanism, different from the spontaneous uncatalysed reaction. 

Decomposition of diphenoylperoxide [6109-04-2] (40) in the presence of a fluorescer such as perylene in methylene chloride at 24°C produces chemiluminescence matching the fluorescence spectmm of the fluorescer with perylene was reported to be 10 5% (135). The reaction follows pseudo-first-order kinetics with the observed rate constant increasing with fluorescer concentration according to = k [flr]. Thus the fluorescer acts as a catalyst for peroxide decomposition, with catalytic decomposition competing with spontaneous thermal decomposition. An electron-transfer mechanism has been proposed (135). 

Only in 1961 did Woodward and Olofson succeed in elucidating the true mechanism of this interesting reaction by making an extensive use of spectroscopic methods. The difficulty was that the reaction proceeds in many stages. The isomeric compounds formed thereby are extremely labile, readily interconvertible, and can be identified only spectroscopically. The authors found that the attack by the anion eliminates the proton at C-3 (147) subsequent cleavage of the N—0 bond yields a -oxoketene imine (148) whose formation was established for the first time. The oxoketene imine spontaneously adds acetic acid and is converted via two intermediates (149, 150) to an enol acetate (151) whose structure was determined by UV spectra. Finally the enol acetate readily yields the W-acyl derivative (152). 

Jn light of the fact that tertiary alkyl halides undergo spontaneous dissociation to yield a carbocation plus halide ion (Problem 10.40) propose a mechanism for the following reaction ... 

---