REACTIONS OF SUGAR CHLOROSULFATES: VII. SOME CONFORMATIONAL ASPECTS

1966 ◽  
Vol 44 (13) ◽  
pp. 1483-1491 ◽  
Author(s):  
A. G. Cottrell ◽  
E. Buncel ◽  
J. K. N. Jones
Keyword(s):  
Transition State ◽  
Sulfuryl Chloride ◽  
Reaction Conditions ◽  
Steric Interactions

The reaction of sulfuryl chloride with several 1,6-anhydro-hexosans has yielded crystalline, fully chlorosulfated derivatives. Replacement of the chlorosulfate moieties by chlorodeoxy groups could not be achieved under the reaction conditions employed. This non-reactivity is discussed in terms of steric interactions in the transition state for substitution.An examination of some chloro-substituted sugar chlorosulfates confirmed that an axial chlorodeoxy group in a glycopyranoside deactivates a neighboring equatorial chlorosulfate group and thus prevents further chlorodeoxy groups being introduced into such positions. Methyl α-D-altropyranoside, methyl α-L-rhamnopyranoside, methyl α-D-lyxopyranoside, L-rhamnose, and D-lyxose were reacted with sulfuryl chloride. The resulting products were those expected if these sugars reacted primarily in the C1 conformation.

Effect of cyclodextrin on elimination reactions

1999 ◽  
Vol 77 (5-6) ◽  
pp. 860-867 ◽  
Author(s):  
Luis Viola ◽  
Rita H de Rossi
Keyword(s):  
Inclusion Complex ◽  
Transition State ◽  
Rate Constant ◽  
Reaction Rate ◽  
Basic Solution ◽  
Substitution Product ◽  
Reaction Conditions ◽  
Pure Solvent ◽  
Elimination Reactions

The reaction of 1-bromo-2-X-2-(Y-phenyl) ethane derivatives (1: X = Y = H; 2: X = Ph, Y = H; 3: X = H, Y = 4-Ac; 4: X = H, Y = 3-NO2; 5: X = H, Y = 4-NO2; 6: X = H, Y = 3-Me; 7: X = H, Y = 4-Me) in basic solution was studied, and in most cases, only the elimination product is formed. Only (2-bromo-1-phenylethyl)benzene, 2, yielded significant substitution product, and this yield decreased with the concentration of HO-. Addition of cyclodextrin (β-CD) diminished (about half for 0.02 M cyclodextrin concentration) the reaction rate of all substrates but 4 and 5. In the latter two cases, the rate rises. The observed rate-constant value at 0.5 M NaOH is 6.78 × 10-4 s-1 (at 40°C) and 1.80 × 10-3 s-1 (at 25°C) for 4 and 5, respectively. Under the same reaction conditions but with 0.01 M β-CD, the corresponding rates were 7.70 × 10-4 s-1 and 5.20 × 10-3 s-1. The elimination yield for 2 increased from 64 to 98% when the β-CD changed from zero to 0.02 M at 0.5 M NaHO. Also, there was an increase in the relative elimination products of 20-40% for compounds 6 and 7. The Hammet ρ values were 1.3 and 2.3 for the reaction in pure solvent and in the presence of β-cyclodextrin, indicating an increase in the negative character of the transition state for the reactions in the latter conditions. The results are interpreted in terms of the formation of an inclusion complex whose structure depends on the substrate.Key words: cyclodextrin, elimination reactions, inhibition, catalysis.

Reactions of enantiopure cyclic diols with sulfuryl chloride

2014 ◽  
Vol 12 (13) ◽  
pp. 2128-2136 ◽  
Author(s):  
Derek R. Boyd ◽  
Narain D. Sharma ◽  
Magdalena Kaik ◽  
Peter B. A. McIntyre ◽  
John F. Malone ◽  
...  
Keyword(s):  
Sulfuryl Chloride ◽  
Reaction Conditions ◽  
Cyclic Sulfates

Monocyclic allyliccis-1,2-diols on reaction with sulfuryl chloride can either give thetrans-2-chloro-1-sulfochloridates or the cyclic sulfates depending on the reaction conditions. The former compounds can be hydrolysed totrans-1,2 chlorohydrins.

scholarly journals New insights into the mechanism of Schiff base synthesis from aromatic amines in the absence of acid catalyst or polar solvents

2019 ◽  
Author(s):  
Pedro J Silva
Keyword(s):  
Transition State ◽  
Aromatic Amines ◽  
Density Functional ◽  
Large Scale ◽  
Reaction Pathway ◽  
Acid Catalyst ◽  
Functional Study ◽  
Computational Studies ◽  
Reaction Conditions ◽  
Polar Solvents

Extensive computational studies of the imine synthesis from amines and aldehydes in water have shown that the large-scale structure of water is needed to afford appropriate charge delocalisation and enable sufficient transition state stabilisation. These insights cannot, however, be applied to the understanding of the reaction pathway in apolar solvents due their inability to form extensive hidrogen-bonding networks. In this work, we perform the first computational studies of this reaction in apolar conditions. This density-functional study of the reaction of benzaldehyde with four closely related aromatic amines (aniline, o-toluidine, m-toluidine and p-toluidine) shows that an additional molecule of amine may provide enough stabilization of the first transition state even in the absence of a hydrogen bonding network. Our computations also show that the second reaction step cannot take place unless an extra proton is added to the system but, crucially, that reaction rate is so high that even picomolar amounts of protonated base are enough to achieve realistic rates. Additional computations show that those minute amounts of protonated base may be obtained under reaction conditions without the addition of extraneous acid through the auto-protolysis of the amines themselves. To our knowledge, this is the first report of a role for the auto-protolysis of anilines in their extensive reactional repertoire.

scholarly journals New insights into the mechanism of Schiff base synthesis from aromatic amines in the absence of acid catalyst or polar solvents

2019 ◽  
Author(s):  
Pedro J Silva
Keyword(s):  
Transition State ◽  
Aromatic Amines ◽  
Density Functional ◽  
Large Scale ◽  
Reaction Pathway ◽  
Acid Catalyst ◽  
Functional Study ◽  
Computational Studies ◽  
Reaction Conditions ◽  
Polar Solvents

Extensive computational studies of the imine synthesis from amines and aldehydes in water have shown that the large-scale structure of water is needed to afford appropriate charge delocalisation and enable sufficient transition state stabilisation. These insights cannot, however, be applied to the understanding of the reaction pathway in apolar solvents due their inability to form extensive hidrogen-bonding networks. In this work, we perform the first computational studies of this reaction in apolar conditions. This density-functional study of the reaction of benzaldehyde with four closely related aromatic amines (aniline, o-toluidine, m-toluidine and p-toluidine) shows that an additional molecule of amine may provide enough stabilization of the first transition state even in the absence of a hydrogen bonding network. Our computations also show that the second reaction step cannot take place unless an extra proton is added to the system but, crucially, that reaction rate is so high that even picomolar amounts of protonated base are enough to achieve realistic rates. Additional computations show that those minute amounts of protonated base may be obtained under reaction conditions without the addition of extraneous acid through the auto-protolysis of the amines themselves. To our knowledge, this is the first report of a role for the auto-protolysis of anilines in their extensive reactional repertoire.

scholarly journals Selecting Between Two Transition States by Which Water Oxidation Intermediates on an Oxide Surface Decay

2019 ◽  
Author(s):  
Xihan Chen ◽  
Daniel J. Aschaffenburg ◽  
Tanja Cuk
Keyword(s):  
Transition State ◽  
Band Gap ◽  
Water Oxidation ◽  
Activation Barrier ◽  
Transition States ◽  
Charge Trapping ◽  
State Theory ◽  
Oxide Surface ◽  
Reaction Conditions ◽  
Hole Trapping

<p>While catalytic mechanisms on electrode surfaces have been proposed for decades, the pathways by which the product’s chemical bonds evolve from the initial charge-trapping intermediates have not been resolved in time. Here, we discover a reactive population of charge-trapping intermediates with states in the middle of a semiconductor’s band-gap to reveal the dynamics of two parallel transition state pathways for their decay. Upon photo-triggering the water oxidation reaction from the n-SrTiO<sub>3</sub> surface with band-gap, pulsed excitation, the intermediates’ microsecond decay reflects transition state theory (TST) through: (1) two distinct and reaction dependent (pH, T, Ionic Strength, and H/D exchange) time constants, (2) a primary kinetic salt effect on each activation barrier and an H/D kinetic isotope effect on one, and (3) realistic activation barrier heights (~0.4-0.5 eV) and TST pre-factors (~10<sup>11</sup> -10<sup>12</sup> Hz). A photoluminescence from mid-gap states in n-SrTiO<sub>3</sub> reveals the reaction dependent decay; the same spectrum was previously assigned by us to hole-trapping at parallel Ti-O<sup>·</sup>-Ti (bridge) and perpendicular Ti-O<sup>·</sup> (oxyl) O-sites using <i>in-situ</i> ultrafast vibrational and optical spectroscopy. Therefore, the two transition states are naturally associated with the decay of these respective intermediates. Furthermore, we show that reaction conditions select between the two pathways, one of which reflects a labile intermediate facing the electrolyte (the oxyl) and the other a lattice oxygen (the bridge). Altogether, we experimentally isolate an important activation barrier necessary for water oxidation, which is necessary for designing water oxidation catalysts for high O<sub>2</sub> turn-over. Moreover, in isolating it, we identify competing mechanisms for O<sub>2</sub> evolution at surfaces and show how to use reaction conditions to select between them.<b></b></p>

π-Facial stereoselectivity in the Diels–Alder reactions of a rigid carbocyclic diene: spiro(bicyclo[2.2.1]heptane-2,1′-[2,4]cyclopentadiene)

1991 ◽  
Vol 69 (1) ◽  
pp. 179-184 ◽  
Author(s):  
D. Jean Burnell ◽  
Zdenek Valenta
Keyword(s):  
Transition State ◽  
Key Words ◽  
Diels Alder ◽  
Steric Interactions

The plane-nonsymmetrical diene spiro(bicyclo[2.2.1]heptane-2,1′-[2,4]cyclopentadiene) (2) was synthesized, and the π-facial stereoselectivity of its Diels–Alder cycloadditions with three cyclic dienophiles was examined. Adduct ratios were very similar, and the selectivity is surmised to be mainly the result of steric interactions at the transition state. Key words: facial stereoselectivity, Diels–Alder, cycloaddition.

scholarly journals Reduction of Cyclopropanecarboxylic Acids by Borane, a Chemoselective Reduction Sensitive to Steric Interactions and Reaction Conditions

2001 ◽  
Vol 2001 (4) ◽  
pp. 133-134 ◽  
Author(s):  
Leiv K. Sydnes ◽  
Paula F. F. Pereira ◽  
Marcel Sandberg ◽  
Hans H. Øvrebø
Keyword(s):  
Reaction Temperature ◽  
Reaction Conditions ◽  
Steric Interactions ◽  
Steric Influence

A number of cyclopropanecarboxylic acids have been reduced by BH3 reagents in THF to the corresponding cyclopropyl alcohols; the yield is sensitive to the steric influence of the substituents attached to the ring, the reaction temperature, and the nature of the borane reagent.

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