Hydrogen, atomic optical

Lamb, W.E., Retherford, R.C., 1947, Fine Structure of the Hydrogen Atom by a Microwave Method, Phys. Rev. 72, 241 Mandel, L., Wolf, R, 1995, Optical Coherence and Quantum Optics, Cambridge University Press Newton, 1952, Opticks, Dover... 

A subsequent detailed analysis of the permanganate oxidation of the tertiary hydrogen atom of 4-phenylvaleric acid in 2.5 M potassium hydroxide solution supports the caged radical mechanism. The reaction order is two overall, A h/ d is ca. 11.5, ring substitution has little elfect on the rate (p 0) and the oxidation proceeds with a net 30-40 % retention of optical configuration. 

This reaction is the reverse of the initial ketyl radical formation by the benzophenone triplet and is therm Q4ynamically favorable. The experiments using optically active alcohols as source of hydrogen atoms show, however, that under normal conditions this reaction is unimportant. This is probably due to other, more efficient pathways for reaction of the ketyl radicals or perhaps to diffusion rates which separate the radicals before reverse transfer can occur. That this reaction can be important in some cases even without the presence of sulfur compounds was shown by studying the photoreduction of benzophenone in optically active ethers.<68) Although the reaction of benzophenone in methyl 2-octyl ether is only 0.17 times as fast as that in isopropanol, ethers can be used as sources of hydrogen atoms for photoreduction ... 

Abstraction of a hydrogen atom from C3 of ( )-2-chloropentane produces a radical that is chiral (it contains a stereocenter at C2). This chiral radical can then react with chlorine at one face [path (a)] to produce (2lS,3.S)-2,3-dichloropentane and at the other face [path (b)] to yield (2 S, 3i )-2,3-dichloropentane. These two compounds are diastereomers, and they are not produced in equal amounts. Each product is chiral, and each alone would be optically active. 

O—H bonds, hydrogen atom abstraction from, 9,127 Organic materials for second-order non-linear optics, 32,121 Organic reactivity, electron-transfer paradigm for, 35, 193 Organic reactivity, structure determination of, 35,67... 

It is possible to use isolated, partially purified enzymes (dehydrogenases) for the reduction of ketones to optically active secondary alcohols. However, a different set of complications arises. The new C H bond is formed by delivery of the hydrogen atom from an enzyme cofactor, nicotinamide adenine dinucleotide (phosphate) NAD(P) in its reduced form. The cofactor is too expensive to be used in a stoichiometric quantity and must be recycled in situ. Recycling methods are relatively simple, using a sacrificial alcohol, or a second enzyme (formate dehydrogenase is popular) but the real and apparent complexity of the ensuing process (Scheme 8)[331 provides too much of a disincentive to investigation by non-experts. 

Replacement of a hydrogen atom by deuterium in 1 butanol by ID has created optical activity. 

Rychnovsky et al. considered the formation of achiral conformers from chiral molecules and trapping the prochiral radical with a hydrogen atom donor based on memory of chirality (Scheme 12) [41], The photo-decarboxylation of optically active tetrahydropyran 40 leads to an intermediate 43, which now does not contain a stereocenter. If the intermediate 43 can be trapped by some hydrogen atom source before ring inversion takes place, then an optically active product 41 will be formed. This is an example of conformational memory effect in a radical reaction. It was reported that the radical inversion barrier is low (< 0.5 kcal/mol) while the energy for chair flip 43 44 is higher (5 to... 

A closely related example involving a seven-membered transition state (6) hydrogen atom abstraction in the crystalline state is shown in Scheme 9. Based on earlier work by Wagner and coworkers [38], Cheung, Rademacher, Scheffer, and Trotter prepared carboxylic acid 41a and treated it with a variety of optically pure amines to form chiral salts 41b [39]. Irradiation of crystalline samples of the salts followed by workup with ethereal diazomethane afforded the chiral in-... 

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