Racemization


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racemization

[‚rā·sə·mə′zā·shən]
(organic chemistry)
A process by which an optically active form of a substance is converted into a racemic mixture.

Racemization

 

the formation of an optically inactive product (racemate) as a result of a reaction involving an asymmetric atom. Racemization is caused by the appearance of an intermediate compound (or transition state), not itself possessing an asymmetric atom, which has an equal probability of yielding optical antipodes. The antipodes, in turn, form racemic compounds. The racemization of carboxylic acids, for example, involves enolization:

Racemization occurs in reactions leading to the formation of the flat carbonium ion and in reactions that are carried out through free radicals.

References in periodicals archive ?
30) to have advantages over derivatization in organic solvents: little or no racemization occurred and excess reagent was destroyed, eliminating GC-MS interference.
The majority of these assays use N-trifluoroacetyl-L-prolyl chloride (14, 20, 21) or the corresponding N-heptafluorobutyryl derivative (15, 22), reagents that have been noted in the literature for their lack of stereochemical purity, their instability, and unpredictable racemization (23-27); therefore, some considerable care is required for the effective use of these reagents.
These authors describe a sequence of lacustrine, lake-shore and dune deposits at the Williams Point site, Lake Eyre, that have been cross-dated by 14C (both conventional and AMS), TL, 230Th/234U and amino-acid racemization (AAR).
Microbially-induced promotion of amino acid racemization in bone: isolation of the microorganisms and the detection of their enzymes, Journal of Archaeological Science 20: 159-68.
Various 'absolute' dating techniques, namely thermoluminescence (TL) of sediments and flints, electron spin resonance (ESR) of horse teeth and radiocarbon and also relative dating techniques such as amino-acid racemization rate determinations have been applied to material from Hoxne.
The similarity to Swanscombe, supported by results from amino-acid racemization, suggests a correlation with Oxygen Isotope Stage 11 (c.
Pleistocene chronologies should be constructed using the widest range of appropriate dating techniques -- such as radiocarbon, luminescence, electronspin resonance, uranium series and amino-acid racemization.
An amino acid racemization chronology of Tabun, in Ronen (1982): 43-54.
Amino acid racemization (AAR) dating has been attempted on rock paintings in South Africa (Pager 1972: 356-9) and in the United States of America (McCarthy et al.
This racemization usually comes about as a result of faulty manufacturing procedures, such as at the point that laetrile was extracted from its source in apricot kernels in a substandard factory.
In the samples prepared with a tin(II) 2-ethylhexanoate as the catalyst, racemization can occur during polymerization, which strongly influences stereoregularity of poly(L-lactide), even with the isosorbide in the main chains.
alpha]-Methylacyl coenzyme A racemase (AMACR) is an enzyme that catalyzes the racemization of [alpha]-methyl-branched carboxylic coenzyme A thioesters.