Biomedical subjects

G K Prakash

Publications and source records attributed to G K Prakash.

21 records · Page 2Linked to original sources

PubMed1981

C NMR chemical shift correlations in application of "tool of increasing electron demand" to stable long-lived carbocations: Comprehensive evaluation.

The reliability of (13)C NMR chemical shift correlations in the application of the "tool of increasing electron demand" to stable long-lived carbocationic systems is demonstrated by a comprehensive analysis of 22 stable aryl-substituted carbocationic systems. The observation of slopes of less than unity in such chemical shift correlations for several cationic systems has been attributed to additional charge delocalizing mechanisms present in the system (such as homoallylic, cyclopropyl, and pi conjugations). The onset of nonclassical sigma-delocalization in 2-aryl-2-norbornyl cations with electron withdrawing-substituents previously observed was further verified by using sigma(C+) substituent constants. Difficulties in relating the C(alpha)NMR shifts in different carbocationic systems are also discussed.

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PubMed1977

C nuclear magnetic resonance study of five- and six-coordinated carbon in nonclassical organometallic compounds: Dimeric trialkyl-, tricyclopropyl-, and triarylaluminums and some nido and closo carboranes.

A (13)C nuclear magnetic resonance spectroscopic study of dimeric trimethyl-, triethyl-, tricyclopropyl-, and triarylaluminums is reported. The five-coordinated bridging carbons are found consistently more shielded than the terminal carbons, in accordance with the increased p-character of the former. The nature of bridging two-electron three-centered Al-C-Al bonds is discussed. (13)C nuclear magnetic resonance shifts of several nido and closo carboranes containing five and six coordinated carbons and their (13)C-(1)H spin-spin coupling constants were also obtained. The relationship between the carbon chemical shifts and coordination number of the carbon atom is discussed. There is approximately a 20- to 40-ppm shielding of the (13)C chemical shifts of five- and six-coordinated carbons, compared with those of four valent carbons, with a simultaneous general increase of J(C-H) coupling constants.

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PubMed1976

The unusual Favorskii-Nazarov reaction of dicyclopropyl ketone.

Dicyclopropyl ketone under Favorskii-Nazarov reaction conditions neither gave tetracyclopropylethylene glycol nor 1,1,4,4-tetracyclopropyl-1,4-butanediol by ether incorporation as expected. The hitherto unknown 1,1,5-tricyclopropyl-1-hydroxypentan-5-one is obtained, presumably through the intermediacy of a dianion which nucleophilically attacks the neutral ketone through the cleavage of the cyclopropyl bond.

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