Déshydratation des diols-1,2 α,β-éthyléniques IV: rôle de la stéréomutation des carbocations allyliques α-hydroxylés sur l'orientation des réactions observées

1980 ◽  
Vol 58 (14) ◽  
pp. 1451-1462 ◽  
Author(s):  
Gilbert Dana ◽  
Josyane Gharbi-Benarous ◽  
Sa Le Thi Thuan
Keyword(s):  
Type A ◽  
Steric Effects ◽  
Hydroxyl Group ◽  
Degradation Reaction

The allylic carbocations[Formula: see text]formed during the dehydration of diols of type A[Formula: see text]are found to react by five different processes: three nucleophilic attacks (by solvent at the β or δ positions, or by the intramolecular hydroxyl group at δ), a degradation reaction between Cα, and Cβ and the classical pinacol rearrangement.Nucleophilic attack at the carbon δ is a very efficient reaction and sometimes (for monosubstituted substrates in β, γ or δ) gives quasi-exclusive products: a ketone for the reaction with H2O in δ or a 2,5-dihydrofuran product for the intramolecular reaction.In the case of γ and δ disubstituted carbocations, the selectivity is less and we show that it is possible to analyze the different steric effects commanding the stereomutation equilibrium of the allylic carbocation and so determining the orientation in the dehydration.

Ab Initio Simulations on the Carbonated Apatite Structure

2012 ◽  
Vol 529-530 ◽  
pp. 1-6 ◽  
Author(s):  
Fu Zeng Ren ◽  
Yang Leng ◽  
Xiong Lu
Keyword(s):  
Ab Initio ◽  
Type A ◽  
Hydroxyl Group ◽  
Type B ◽  
Carbonate Group ◽  
Stable Type ◽  
Carbonated Apatite ◽  
Carbonate Ions ◽  
Compensation Mechanisms ◽  
Type Ab

ab initio simulations were employed to investigate the crystal structure of carbonated apatite (CAp). Two possible sites for the carbonate ions in the apatite lattice were considered: carbonate substituting for OH-ion (type-A) and for PO43-ion (type-B). A combined type-AB substitution was also proposed and numerous possible charge compensation mechanisms were treated. The results show that the most stable type-A CAp had its carbonate triangular plane almost parallel to c-axis, making an angle of about 2° at z = 0.46. In the most stable type-B CAp structure, the nearest Ca (2) ion was replaced by a sodium ion and the carbonate group was lying almost flat inb/c-plane. Of all the models considered, mixed substitution type-AB where two carbonate ions replacing one phosphate group and one hydroxyl group shows the most stable structure.

Studies of the Wallach Transformation. II. Steric Effects in Some Symmetrically Disubstituted Azoxybenzenes

1951 ◽  
Vol 4 (2) ◽  
pp. 185
Author(s):  
PH Gore ◽  
GK Hughes
Keyword(s):  
Sulphuric Acid ◽  
Important Influence ◽  
Steric Effects ◽  
Hydroxyl Group ◽  
Azoxy Compounds ◽  
Point Of Entry ◽  
Substituent Group

Study of the behaviour of symmetrical azoxy compounds in the Wallach Transformation shows the important influence of size of a substituent group ortho to the point of entry of the hydroxyl group.�The various processes known to occur in a solution of azoxybenzene in sulphuric acid are discussed.

A Study of Steric Effects on Nitromethylene Acidity and the Mechanism of Epimerization in Partially Blocked Nitro Hexoses

1971 ◽  
Vol 49 (19) ◽  
pp. 3197-3202 ◽  
Author(s):  
Hans H. Baer ◽  
Werner Rank
Keyword(s):  
Potassium Hydroxide ◽  
Potassium Hydroxide Solution ◽  
Alcoholic Solution ◽  
Steric Effects ◽  
Hydroxyl Group ◽  
Henry Reaction ◽  
Hydroxide Solution

The extent of nitronate formation in seven methyl 4,6-O-benzylidene-3-deoxy-3-nitrohexopyranosides and four methyl 4,6-O-benzylidene-2,3-dideoxy-3-nitrohexopyranosides in dilute potassium hydroxide solution was compared by means of u.v. spectroscopy. Considerable differences were found to exist in the nitromethylene acidities, and these were correlated with stereochemical features of the molecules. A facile manno → gluco epimerization occurring in this series was investigated. It was shown that, in alkaline alcoholic solution, the epimerization proceeds by an elimination–addition via an intermediate nitroalkene if the hydroxyl group at C-2 is acetylated. However, if the hydroxyl is free, the nitroalkene is not an intermediate and, in accord with the low nitromethylene acidity in this particular case, the mechanism is suggested to involve a reverse Henry reaction.

RATES OF POLYMERIZATION OF ACRYLATES AND METHACRYLATES IN EMULSION SYSTEMS

1964 ◽  
Vol 42 (4) ◽  
pp. 825-829 ◽  
Author(s):  
K. G. McCurdy ◽  
K. J. Laidler
Keyword(s):  
Steric Hindrance ◽  
Steric Effects ◽  
Hydroxyl Group ◽  
Methyl Ethyl ◽  
Initial State ◽  
Emulsion Systems

The microcalorimeter has been used to obtain rates of polymerization of a number of monomers in emulsion systems. The rates with the acrylates are consistently higher than those with the methacrylates, and this is attributed to less steric hindrance. Low rates found with monomers containing a hydroxyl group are explained as due to solvation in the initial state. In both the acrylates and methacrylates the rates go through a maximum as one goes up the series methyl: ethyl: butyl: hexyl. This is discussed in terms of inductive and steric effects.

Biological and Morphological Studies on Low-Leukemia-Strain Mice with Hodgkin's-Like Neoplasia Induced by Serial Cell-Free Transmission of Leukemic Organs of SJL/J Strain Mice

1968 ◽  
Vol 26 ◽  
pp. 210-211
Author(s):  
S. Fujinaga ◽  
K. Maruyama ◽  
C.W. Williams ◽  
K. Sekhri ◽  
L. Dmochowski
Keyword(s):  
Tissue Culture ◽  
Type A ◽  
Reticulum Cell ◽  
Type B ◽  
Viral Origin ◽  
Serial Transfer ◽  
Strain Mouse ◽  
Morphological Studies ◽  
Cell Neoplasm ◽  
Free Material

Yumoto and Dmochowski (Cancer Res.27, 2098 (1967)) reported the presence of mature and immature type C leukemia virus particles in leukemic organs and tissues such as lymph nodes, spleen, thymus, liver, and kidneys of SJL/J strain mice with Hodgki's-like disease or reticulum cell neoplasm (type B). In an attempt to ascertain the possibility that this neoplasia may be of viral origin, experiments with induction and transmission of this neoplasm were carried out using cell-free extracts of leukemic organs from an SJL/J strain mouse with spontaneous disease.It has been possible to induce the disease in low-leukemia BALB/c and C3HZB strain mice and serially transfer the neoplasia by cell-free extracts of leukemic organs of these mice. Histological examination revealed the neoplasia to be of either reticulum cell-type A or type B. Serial transfer is now in its fifth passage. In addition leukemic spleen from another SJL/J strain mouse with spontaneous reticulum cell neoplasm (type A) was set up in tissue culture and is now in its 141st serial passage in vitro. Preliminary results indicate that cell-free material of 39th tissue culture passage can reproduce neoplasia in BALB/c mice.

Hepatitis A Antigen in Liver, Bile and Stool

1975 ◽  
Vol 33 ◽  
pp. 340-341
Author(s):  
D.R. Jackson ◽  
J.H. Hoofnagle ◽  
A.N. Schulman ◽  
J.L. Dienstag ◽  
R.H. Purcell ◽  
...  
Keyword(s):  
Hepatitis A ◽  
Liver Enzymes ◽  
Hepatitis A Virus ◽  
Type A ◽  
Initial Study ◽  
Virus Like Particle ◽  
Elevated Liver Enzymes ◽  
Ag Particles ◽  
Ag Particle ◽  
Human Stool

Using immune electron microscopy Feinstone et. al. demonstrated the presence of a 27 nm virus-like particle in acute-phase stools of patients with viral hepatitis, type A, These hepatitis A antigen (HA Ag) particles were aggregated by convalescent serum from patients with type A hepatitis but not by pre-infection serum. Subsequently Dienstag et. al. and Maynard et. al. produced acute hepatitis in chimpanzees by inoculation with human stool containing HA Ag. During the early acute disease, virus like particles antigenically, morphologically and biophysically identical to the human HA Ag particle were found in chimpanzee stool. Recently Hilleman et. al. have described similar particles in liver and serum of marmosets infected with hepatitis A virus (HAV). We have investigated liver, bile and stool from chimpanzees and marmosets experimentally infected with HAV. In an initial study, a chimpanzee (no.785) inoculated with HA Ag-containing stool developed elevated liver enzymes 21 days after exposure.

Detection of Viral Antigens in Mouse and Rat Tumor Cells by Immunoelectron Microscopy Following Periodate-Lysine-Paraformaldehyde (PLP) Fixation

1976 ◽  
Vol 34 ◽  
pp. 252-253
Author(s):  
Y. Ohtsuki ◽  
G. Seman ◽  
J. M. Bowen ◽  
M. Scanlon ◽  
L. Dmochowski
Keyword(s):  
Immunoelectron Microscopy ◽  
Mammary Tumor ◽  
Type A ◽  
Rabbit Serum ◽  
Virus Particles ◽  
Viral Antigens ◽  
Culture Cells ◽  
Mouse Mammary Tumor ◽  
Tumor Virus ◽  
Immunoperoxidase Labeling

Recently, periodate-lysine-paraformaldehyde (PLP) fixation was reported for immunoelectron microscopy (1). In PLP fixation, carbohydrates are oxidized by periodate and cross-linked by lysine; paraformaldehyde stabilizes proteins and lipids. By using PLP fixation, intracytoplasmic type A viral antigens have been previously demonstrated by immunoperoxidase labeling (2). In the present study, PLP fixation has been applied for the detection of the same antigens in mouse mammary tumor culture cells by both immunoferritin and immunoperoxidase methods. Rabbit anti-intracytoplasmic type A virus serum (anti-A), kindly provided by Dr. M. Muller (3), rabbit anti-strain A mouse mammary tumor virus (anti-MMTV) and preimmune rabbit serum as control were used to detect viral antigens in cells of C3H/HeJ strain mouse mammary tumor culture. Attempts have been also made to demonstrate peroxidase labeling of type C virus particles in frozen sections of an SD-MSV-induced NZB rat bone tumor tissue by rabbit anti-MuLV serum.

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