Methyl migration by epoxide cleavage. The effect of carbonium ion stabilisation by a neighbouring double bond on the direction of migration on cleavage of 9β,11β-epoxy-4,4-dimethylandrost-5-ene-3,17-dione

1970 ◽  
Vol 0 (19) ◽  
pp. 1271-1271 ◽  
Author(s):  
J. W. ApSimon ◽  
J. M. Rosenfeld
Keyword(s):  
Double Bond ◽  
Carbonium Ion

The General Dienol: Benzene Rearrangement of Ring a of the Steroids

2005 ◽  
Vol 2005 (3) ◽  
pp. 141-146 ◽  
Author(s):  
James R. Hanson
Keyword(s):  
Double Bond ◽  
Aromatic Ring ◽  
Ion Source ◽  
Carbonium Ion ◽  
Wide Range

The dienol: benzene type of rearrangement of steroids, to form compounds with an aromatic ring A, occurs under acid-catalysed conditions with a wide range of substrates containing two double bond equivalents and a carbonium ion source on rings A and B.

Chemical Basis of the Sulfo-phospho-vanillin Reaction for Estimating Total Serum Lipids

1972 ◽  
Vol 18 (3) ◽  
pp. 199-202 ◽  
Author(s):  
Joseph A Knight ◽  
Shauna Anderson ◽  
James M Rawle
Keyword(s):  
Double Bond ◽  
Carbonyl Group ◽  
Serum Lipids ◽  
Gravimetric Method ◽  
Initial Step ◽  
Total Serum ◽  
Phosphate Ester ◽  
Unsaturated Lipids ◽  
Carbonium Ion ◽  
Concentrated Sulfuric Acid

Abstract Results with the "sulfo-phospho-vanillin" reaction, much used for determining total serum lipids, have been favorably compared with those for the gravimetric method. We investigated the basic chemistry of the reaction and determined the reactivity of this single reagent with various lipids. Our results suggest that: (a) The reaction requires a carbon-carbon double bond. (b) Concentrated sulfuric acid reacts with unsaturated lipids in the initial step to form a carbonium ion. (c) Phosphoric acid reacts with vanillin to produce a phosphate ester, with a resulting increase in the reactivity of the carbonyl group. (d) The carbonium ion reacts with the carbonyl group of phosphovanillin to form a colored compound, which is stabilized by resonance. (e) Unsaturated compounds with more than one double bond react, but reaction may vary with steric hindrance. (f) The method is reasonably precise, but its accuracy depends primarily on the reference standard used.

Reversible addition of a carbonium ion to a double bond

1977 ◽  
Vol 99 (21) ◽  
pp. 7090-7091 ◽  
Author(s):  
Martin Saunders ◽  
John R. Lloyd
Keyword(s):  
Double Bond ◽  
Carbonium Ion ◽  
Reversible Addition

THE REACTION OF POLYISOPRENE WITH TITANIUM TETRACHLORIDE

1963 ◽  
Vol 41 (4) ◽  
pp. 937-953 ◽  
Author(s):  
Morton A. Golub ◽  
Jorge Heller
Keyword(s):  
Double Bond ◽  
Titanium Tetrachloride ◽  
First Order ◽  
First Order Kinetics ◽  
Carbonium Ion ◽  
Fused Ring ◽  
Ring Structures ◽  
Methylene Groups ◽  
Pseudo First Order ◽  
Total Disappearance

The reaction of titanium tetrachloride with hevea, balata, and synthetic cis-polyisoprene in benzene at 80 °C has been studied. The most prominent change in the infrared spectra of these polymers is the nearly total disappearance of the 12 μ band after prolonged reaction with TiCl4. The diminution of this band, associated with the loss of the original —C(CH3)=CH— units, whether cis or trans, followed pseudo-first-order kinetics, the rate varying with [TiCl4]n, where n is 1.0 in the case of the cis polymers and 1.5 in the case of the trans polymer. Contrary to previous reports, practically no cis–trans isomerization of polyisoprene occurs in the course of this reaction, the data being explained entirely by cyclization. With the help of cis-1,4 polymers of isoprene-3-d and 2-methyl-d3-1,3-butadiene-1,1-d2, it was concluded that cyclization, involving a TiCl4-induced carbonium ion mechanism, leads to the formation of six-membered rings fused into predominantly bicyclic structures, connected by methylene groups and/or uncyclized monomer units. Each of the fused ring structures contains a single tetra-, tri-, or di-substituted double bond, the relative amounts of which are in the order tetra- > tri- > di-substituted.

Vinyl sulfide hydrolysis

1977 ◽  
Vol 55 (3) ◽  
pp. 548-551 ◽  
Author(s):  
Robert A. McClelland
Keyword(s):  
Double Bond ◽  
Proton Transfer ◽  
Acid Solutions ◽  
Vinyl Ethers ◽  
Vinyl Sulfide ◽  
Carbonium Ion ◽  
Carbon Double Bond ◽  
Carbonium Ions ◽  
Vinyl Sulfides ◽  
Hydrolysis Of

The hydrolysis of vinyl sulfides in acid solutions is shown to proceed via a mechanism analogous to that of vinyl ethers, with slow proton transfer to the carbon–carbon double bond to produce a sulfur stabilized carbonium ion. Relative rates of hydrolysis of compounds RXCH=CH2 are CH3S—, 41; CH3O—, 1500; C6H5S—, 1; and C6H5O—, 10.5. This order is compared with that of other systems which produce similar stabilized carbonium ions.

Stereoselective synthesis of dioxabicycles from 1-C-allyl-2-O-benzyl-glycosides — An intramolecular cyclization between 2-O-benzyl oxygen and the allyl double bond

2006 ◽  
Vol 84 (4) ◽  
pp. 597-602 ◽  
Author(s):  
An-Tai Wu ◽  
Tian Yi ◽  
Huawu Shao ◽  
Shih-Hsiung Wu ◽  
Wei Zou
Keyword(s):  
Double Bond ◽  
Intramolecular Cyclization ◽  
Stereoselective Synthesis ◽  
Carbonium Ion

Addition of a proton to the double bond of 1-C-allyl-O-benzylglycosides gave a 2′-carbonium ion, which in turn reacted intramolecularly, in a regio- and diastereo-selective manner, with the nucleophilic oxygen of the 2-O-benzyl group to form an oxonium intermediate. Subsequent cleavage of the benzyl C—O bond led to dioxabicycles in moderate yields. Surprisingly, opposite diastereoselectivities were observed from 1-C-allylglycofuranosides and 1-C-allylglycopyranosides, which produced 2,2′-trans- and 2,2′-cis-dioxabicycles, respectively.Key words: C-glycoside, olefin, cyclization, oxocarbonium, dioxabicycles.

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