Stereoelectronic control in acetal formation

1980 ◽  
Vol 58 (23) ◽  
pp. 2531-2531 ◽  
Author(s):  
Normand Beaulieu ◽  
Robert A. Dickinson ◽  
Pierre Deslongchamps
Keyword(s):  
Experimental Evidence ◽  
Room Temperature ◽  
Equilibrium Mixture ◽  
Anomeric Effect ◽  
Equilibrium Study ◽  
Stereoelectronic Effects ◽  
Stereoelectronic Control ◽  
Acidic Conditions ◽  
Cis And Trans

The cyclization under acidic conditions of bicyclic and monocyclic hydroxypropyl methoxytetrahydropyrans 1 and 4 is reported. At room température, compound 1 gives only cis tricyclic acetal 2. At reflux, compound 2 equilibrates to yield a mixture of cis and trans tricyclic acetals 2 (45%) and 3 (55%). Compound 4 gives directly the equilibrium mixture of cis and trans bicyclic acetals 5 (55%) and 6 (45%) at room température. The specific formation of 2 from 1 constitutes strong experimental evidence that acetal formation is controlled by stereoelectronic effects. The anomeric effect can be estimated [Formula: see text] from the equilibrium study of 2 and 3. This value confirms the result previously obtained by Descotes (9).

Some reactions of 2,4-dimethoxytetrahydropyrans

1969 ◽  
Vol 47 (17) ◽  
pp. 3099-3106 ◽  
Author(s):  
M. J. Baldwin ◽  
R. K. Brown
Keyword(s):  
Room Temperature ◽  
Equilibrium Mixture ◽  
Anomeric Effect ◽  
Temperature Reaction ◽  
Trans Isomers ◽  
Kcal Mole ◽  
A Value ◽  
Cis And Trans Isomers ◽  
Acid Catalyzed ◽  
Cis And Trans

Acid-catalyzed elimination of methanol from 2,4-dimethoxytetrahydropyran (1) produces 2-methoxy-5,6-dihydro-2H-pyran (3) rather than the expected olefin 4-methoxy-3,4-dihydro-2H-pyran (2).The reaction of 1,3-dibromo-5,5-dimethylhydantoin with 3 in ether – methanol gives a 2:1 mixture of the isomers 3β-bromo-2α,4α-dimethoxytetrahydropyran (5a) and 3α-bromo-2α,4β-dimethoxytetrahydropyran (5b) respectively. A rationale is given to explain the preponderance of 5a over 5b and the highly selective attack of the bromine of the hydantoin and the methanol on C-3 and C-4 respectively of the double bond of 3. Reduction of 5ab with zinc in ethanol provides only compound 3.The room temperature reaction of 1 in a mixture of water and 1,2-dimethoxyethane containing Amberlite IR-120, produces 2-hydroxy-4-methoxytetrahydropyran (6) as an equilibrium mixture of cis and trans isomers in the ratio 1:1. This gave a value of 0.9 kcal/mole for the anomeric effect in 6. Pyrolysis of the derivative, 2-acetoxy-4-methoxytetrahydropyran failed to produce the olefin 2 and resulted only in extensive decomposition.

Cis- and trans-2,4-dimethoxytetrahydropyran. Models for the study of the anomeric effect

1968 ◽  
Vol 46 (9) ◽  
pp. 1543-1548 ◽  
Author(s):  
F. Sweet ◽  
R. K. Brown
Keyword(s):  
Good Yield ◽  
Methoxy Group ◽  
Equilibrium Mixture ◽  
Anomeric Effect ◽  
Kcal Mole ◽  
Mild Acid Hydrolysis ◽  
Acid Catalyzed ◽  
Cis And Trans ◽  
Hydrolysis Of ◽  
Mild Acid

Acid-catalyzed methanolysis of 2-methoxy-5,6-dihydro-2H-pyran gave, in good yield, a 4.0:1.0 mixture of trans- and cis-2,4-dimethoxytetrahydropyran. Mild acid hydrolysis of 2-methoxy-5,6-dihydro-2H-pyran followed by acid-catalyzed reaction with methanol gave a cis-trans mixture of 4-hydroxy-2-methoxytetrahydropyran in very poor yield.From the equilibrium mixture of trans- and cis-2,4-dimethoxytetrahydropyran (4.0:1.0), the magnitude of the anomeric effect of the 2-methoxy group was calculated to be 1.4 kcal/mole.

Nuclear Magnetic Resonance Experiments on Acetals. 35. Proton Magnetic Resonance Spectra and Quantitative Conformational Analysis of 4-Fluoromethylated-6-Me-1,3-dioxanes

1972 ◽  
Vol 50 (3) ◽  
pp. 412-422 ◽  
Author(s):  
P. Dirinck ◽  
M. Anteunis
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Dipole Moment ◽  
Magnetic Resonance ◽  
Conformational Analysis ◽  
Proton Magnetic Resonance ◽  
Room Temperature ◽  
Anomeric Effect ◽  
In Trans ◽  
Cis And Trans ◽  
Absolute Shift

4-Substituted ([Formula: see text] and CH2F)-6-Me-1,3-dioxanes together with model derivatives (cis- and trans-4-CHnF3−n-6-t. Bu-1,3-dioxane, and 2-Me-4,6-disubstituted 1,3-dioxanes) were prepared and their p.m.r. spectra analyzed, using i.a. INDOR techniques. Special features which correlate configuration and p.m.r. data are discussed and especially the fluorine–hydrogen (long-range) couplings have been studied. From vicinal (ring) coupling data (using appropriate models), from the vicinal exo-couplings 3J(H4,CF3−nHn) and from absolute shift values, the equilibria were obtained in the conformational heterogenous trans-4-CHnF3−n-6-Me-1,3-dioxanes (n = 0 → 2). The results, according to the different methods, are mutually in excellent agreement, as is also the case for ΔG0(CF3), obtained approximately from dipole moment measurements. The anomeric effect is pronounced, and the conformer with the axial fluoromethylated substituent is the preferred one (CF3:76%; CF2H:62%) at room temperature in CS2. For CH2F the contrary seems to be the case (presumably for entropy reasons also). Finally ΔH0(chair–twist) was evaluated at 3.7 kcal/mol [Formula: see text] using 2J(H2) criteria in trans-4-CF3-6-t. Bu-1,3-dioxane.

scholarly journals First experimental evidence of the piezoelectric nature of struvite

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jolanta Prywer ◽  
Rafał Kruszyński ◽  
Marcin Świątkowski ◽  
Andrzej Soszyński ◽  
Dariusz Kajewski ◽  
...  
Keyword(s):  
Thermal Decomposition ◽  
Experimental Evidence ◽  
Heating Rate ◽  
Transformation Temperature ◽  
Room Temperature ◽  
Piezoelectric Coefficient ◽  
Piezoelectric Properties ◽  
Parallel Plates ◽  
Gel Growth ◽  
Growth Technique

AbstractIn this paper, we present the first experimental evidence of the piezoelectric nature of struvite (MgNH4PO4·6H2O). Using a single diffusion gel growth technique, we have grown struvite crystals in the form of plane parallel plates. For struvite crystals of this shape, we measured the piezoelectric coefficients d33 and d32. We have found that at room temperature the value of piezoelectric coefficient d33 is 3.5 pm/V, while that of d32 is 4.7 pm/V. These values are comparable with the values for other minerals. Struvite shows stable piezoelectric properties up to the temperature slightly above 350 K, for the heating rate of 0.4 K/min. For this heating rate, and above this temperature, the thermal decomposition of struvite begins, which, consequently, leads to its transformation into dittmarite with the same non-centrosymmetric symmetry as in case of struvite. The struvite-dittmarite transformation temperature is dependent on the heating rate. The higher the heating rate, the higher the temperature of this transformation. We have also shown that dittmarite, like struvite exhibits piezoelectric properties.

scholarly journals Experimental Evidence for Ice Formation at Room Temperature

2008 ◽  
Vol 101 (3) ◽  
Author(s):  
K. B. Jinesh ◽  
J. W. M. Frenken
Keyword(s):  
Experimental Evidence ◽  
Room Temperature ◽  
Ice Formation

FACTORS INFLUENCING THE AMOUNT OF INSULIN EXTRACTABLE FROM BEEF PANCREAS: I. EFFECTS OF AGING FRESH PANCREAS AT ROOM TEMPERATURE

1957 ◽  
Vol 35 (7) ◽  
pp. 527-535 ◽  
Author(s):  
Gerald A. Wrenshall ◽  
Charles H. Best ◽  
W. Stanley Hartroft
Keyword(s):  
Experimental Evidence ◽  
Beta Cells ◽  
Room Temperature ◽  
Second Phase ◽  
Structural Components ◽  
Factors Influencing ◽  
Two Phases ◽  
Early Rise ◽  
Effects Of Aging ◽  
New Formation

Effects on the concentration of extractable insulin of aging fresh beef pancreas at temperatures in the 22–26 °C. range have been described. Two phases of change with time of aging have been observed, describable as a transient increase superimposed on a progressive fall toward zero in the concentration of insulin extractable from the pancreas. In two of the eight experiments reported only the second phase was detected.Various hypotheses concerning the cause of the first phase are considered. The available experimental evidence is considered to support the hypothesis that the early rise in extractable insulin resulted from the continuing new formation of insulin from structural components already present in the cytoplasm of the beta cells at time of exsanguination, or diffusing into it thereafter. The progressive fall in the extractable insulin during the second phase must have resulted from destruction or inactivation of insulin within the pancreas.The bearing of these recent findings on the usage of the term "The insulin content of the pancreas" has been discussed.

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