Secondary Isotope Effects

Halevi, E. Amitai

doi:10.1002/9780470171806.ch4

Cited by 133 publications

(11 citation statements)

References 3 publications

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“…Such small effects, when amplified over many chain reaction steps might be sufficient to slow the generation of toxic autoxidation products and preserve cell viability. The value of the primary KIE for abstraction of the bis-allylic H from 11- 13 C-Lin is roughly comparable to the secondary KIE for the H abstraction off the 11-CHD methylene group [34, 35]. However, we observed that yeast coq9 mutants were nearly as sensitive to treatment with 11- 13 C-Lin as they were to treatment with Lin (Fig.…”

Section: Resultssupporting

confidence: 58%

“…However, the lack of protection afforded by 11- 13 C-Lin, argues against this idea. This is because the bis-allylic H atom at position 11 is predicted to have a primary 13 C KIE (with values up to 1.25 [35]) comparable to the secondary KIE for the bis-allylic 11-H atom adjacent to the D at position 11 in the mono-deuterated Lin. Thus it appears that the presence of D in the radical system is important for this inhibition effect.…”

Section: Discussionmentioning

confidence: 99%

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Small amounts of isotope-reinforced polyunsaturated fatty acids suppress lipid autoxidation

Hill¹,

Lamberson

et al. 2012

Free Radical Biology and Medicine

100

106

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Section: Resultssupporting

confidence: 58%

Section: Discussionmentioning

confidence: 99%

Small amounts of isotope-reinforced polyunsaturated fatty acids suppress lipid autoxidation

Hill¹,

Lamberson

et al. 2012

Free Radical Biology and Medicine

100

106

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“…Instead of hybridization changes, the isotope effect on amine basicity was attributed to an inductive effect . This cannot be due to a simple difference in the electronegativities of H and D because the Born-Oppenheimer approximation guarantees that the electronic wave function is independent of nuclear mass.…”

Section: Secondary Isotope Effects On Basicitymentioning

confidence: 93%

The Logic behind a Physical–Organic Chemist’s Research Topics

Perrin

2016

J. Org. Chem.

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Abstract. Although my research has no common theme or defining area, a coherence connects the diverse topics, insofar as one project leads logically to another. Thus studies on mechanisms of hydrogen exchange in amides and amidines led to the influence of hydrogenbonding and to NMR methods for chemical kinetics, including 2D-EXSY spectroscopy.Another connection was the OH --catalyzed NH exchange in amines that had supported the hypothesis of stereoelectronic control. We therefore analyzed that hypothesis critically, tested it, found counterexamples, and proposed an alternative hypothesis. We next addressed one-bond NMR coupling constants in ethers and the reverse anomeric effect. The latter studies required a highly accurate NMR titration method that we developed to measure the additional steric bulk resulting from protonation of a substituent. This method is also applicable to measuring secondary isotope effects on acidity, and we could demonstrate that they arise from n-* delocalization, not from an inductive effect. Other studies included kinetic isotope effects for both dissociation and H exchange of aqueous NH 4 + , for C-N rotation in amides, and for a hydride transfer. The role of hydrogen-bonding led us to the rotation of NH 4 + within its solvent cage and then to the symmetry of hydrogen bonds. This review article is based on an address presented at the 249th National Meeting of the American Chemical Society in Denver CO, on the occasion of the James Flack Norris Award in Physical-Organic Chemistry. 1 It demonstrates the ways whereby one physicalorganic chemist, and physical-organic chemists in general, have investigated how molecular structure affects chemical reactivity. It also seeks to confirm my claim that "In my opinion, 2 physical organic chemistry represents the intellectual basis of organic chemistry. It asks (and answers!) fundamental questions about how chemical substances behave, and it rationalizes that behavior." 2 The reason that I won the James Flack Norris Award was for my "insight, rigorous analysis, and understanding of mechanisms and reactive intermediates", rather than any distinctive area of research with which I am associated. Instead of choosing one area to review here, I have tried to describe the path of my research for the past 40 years, as an expansion of an earlier article on this topic. 3 Each area seems to have engendered additional questions, leading to additional areas. Often those questions are marked by an intense skepticism, and the answers to those questions are supported by a logical analysis that I am proud of. I hope that this article will be as interesting, informative, and enjoyable to the reader as the research described here has been for me. A Beginner's ResearchMy Ph.D. thesis research was on mercuration of benzene, an electrophilic aromatic substitution that is accelerated by strong acid, and where we measured the H/D kinetic isotope effect. 4 To understand the origin of the acceleration it was necessary to consider acidity functions, including a new one, H...

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“…A more rigorous explanation proposes an electrostatic interaction between the ionic charge and the dipole moments of C À H or C À D bonds. [10] Dipole moment is the product of charge separation and bond length. Owing to anharmonicity, the average CÀH bond is longer than the CÀD, and thus has a larger dipole moment that more effectively stabilizes the negative charge of the carboxylate anion, as (exaggeratedly) suggested in 4 H relative to 4 D. [11] Two estimates of the difference in dipole moments vary widely, 0.0086 D versus 0.0001 D. [10b,6] This is an unresolved issue, and eminent researchers continue to invoke an inductive effect to account for secondary deuterium isotope effects.…”

mentioning

confidence: 99%