Walden inversions

Walden inversion (Section 8.4) Originally, a reaction sequence developed by Paul Walden whereby a chiral starting material was transformed to its enantiomer by a series of stereospecihc reactions. Current usage is more general and refers to the inversion of conhguration that attends any bi-molecular nucleophilic substitution. 

Wald-, wood, forest, wild, -ahom, m. sycamore, -bau, n. silviculture, forestry, -baum, m. forest tree, -boden, m. forest soil. Walden sche Umkehmng. Walden inversion. Wald-gewachs, n. forest plant, -humus m. 

The use of tetra-n-butylammonium fluoride (54) in an aprotic solvent such as acetonitrile may be more advantageous. Foster and colleagues (19, 37) have effected an SN2 type of reaction using this reagent in the conversion of l,2 5,6-di-0-isopropylidene-3-0-p-tolylsulfonyl-D-allofura-nose into the C-3 epimeric fluorodeoxy derivative. Note that whereas potassium fluoride is ineffective in displacing secondary sulfonate esters in sugars, tetra-n-butylammonium fluoride is capable of effecting a displacement with Walden inversion even in a furanose drivative. 

The alio configuration was assigned on the expectation that the last chlorosulfate group at C-3 in 89 was also displaced by a Walden inversion. 

The following Walden cycle has been carried out. Explain the results, and indicate where Walden inversion is occurring. 

Walden inversion (Section 11.1) The inversion of configuration at a chirality center that accompanies an SN2 reaction. 

Maleic acid, structure of, 753 Malic acid, structure of, 753 Walden inversion of, 359-360 Malonic ester, carboxylic acids from, 856-858... 

Walden, Paul, 360 Walden inversion. 359-360 Wang resin, solid-phase peptide synthesis and. 1037 Water, acid-base behavior of, 50 dipole moment of, 39 electrostatic potential map of. 53 nucleophilic addition reactions of, 705-706 pKaof, 51-52... 

In this book the discussion has been restricted to the structure of the normal states of molecules, with little reference to the great part of chemistry dealing with the mechanisms and rates of chemical reactions. It seems probable that the concept of resonance can be applied very effectively in this field. The activated complexes which represent intermediate stages in chemical reactions are, almost without exception, unstable molecules which resonate among several valence-bond structures. Thus, according to the theory of Lewis, Olson, and Polanyi, Walden inversion occurs in the hydrolysis of an alkyl halide by the following mechanism ... 

Stacey started research in an inspiring and stimulating atmosphere that he strove to maintain, add to, and develop when it became his turn to lead the department. His earliest research was with Haworth and his key partner E. L. Hirst [Adv. Carbohydr. Chem. Biochem., 35 (1978) 1 -29] on aspects of the chemistry of glucoheptose. His first publication with them in 1931 was entitled Walden Inversion in the a-Glucoheptose Series, followed in the next year by a report on the methylation of monocarboxylic acids derived from aldoses and the structure of pentamethyl a-gluco-heptonolactone. He found this to be a difficult project because, initially, he could not crystallize his stock of glucoheptose. Then, as later, he found crystallization to be a challenging problem. 

Diiodosilane l2SiH2 1872, prepared by treatment of phenylsilane PhSiHs with iodine, via PhSiH2l, in the presence of catalytic amounts of ethyl acetate at -20 °C, is much more electrophilic than Me3SiI 17 and therefore converts secondary alcohols such as 2-octanol 1871, at room temperature with Walden inversion, into iodides such as 1873 in 93% yield whereas the diol 1874 is nearly quantitatively converted into the monoiodobutane 1875 and only traces of the diiodobutane 1876 [88, 89] (Scheme 12.26). 

Another example is provided by the observation of Ohle and Wilcke16 that whereas 3-tosyl-l,2-isopropylidene-D-glucofuranose (XXXV) is saponified without anhydro ring formation and without Walden inversion, the triacetate of methyl 3-tosyl-/3-D-glucofuranoside (XXXVI) is... 

Walden inversion on C2 has occurred in one of these sequences if in the first, then chitose, chitonic acid and isosaccharic acid have the configuration of D-mannose if in the second, i. e., in the deamination of 2-amino-D-gluconic acid, then chitaric acid and epi-isosaccharic acid are... 

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