Chemical effects of steric strains—XIII

Brown, Herbert C.; Wheeler, Owen H.; Ichikawa, K.

doi:10.1016/0040-4020(57)88041-7

Cited by 90 publications

(29 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Can reproducible rate constants were obtained, the values being found to be independent of the initial concentrations chosen, in agreement with the findings of Brown et al (46) and in confirmation of the assumption of second-order kinetics. The values of k, and k, are summarized in Table 1 and represent the results of at least three independent kinetic runs for each determination.…”

Section: Kinetic Method4supporting

confidence: 80%

“…The data were treated by plotting log,, 4b(a -x)/a(4b -x) against t where a is the initial ketone concentration, b, initial borohydride concentration, and x, concentration of reacted ketone at time t. The slope, equal to k(a -4b)/2.303, where k5 is the second-order rate constant, was computed with a least-squares programme6 on an Olivetti-Underwood Programma 101 desk computer. Figures 2 and 3 (46) was found to be less consistent than the spectrophotometric method.…”

Section: Kinetic Method4mentioning

confidence: 92%

“…Previous rate constants (46) refer to borohydride and, in order that direct comparisons may be made, our values also refer to this rate, despite the fact that our measurements are based on ketone concentrations.…”

Section: Kinetic Method4mentioning

confidence: 99%

“…This feature is not surprising since hydrolysis of sodium borohydride (27), hydrolysis of pyridine alkylboranes (28), and the methanolysis of lithium borohydride (29) all have inverse isotope effects. In the reduction of ketones by borohydride, it has been shown (30,46) that the rate determining step is transfer of the first hydrogen (Fig. 4).…”

Section: The Terms Steric Approach Control Andmentioning

confidence: 99%

See 3 more Smart Citations

Deuterium Isotope Effects in the Reduction of Cyclohexanones. The Concepts of Steric Approach Control and Product Development Control

Wigfield¹,

Phelps²

1972

Can. J. Chem.

View full text Add to dashboard Cite

Definitions for the terms steric approach control and product deuelopment control in relation to the degree of bonding in the transition state are put forward. Kinetic deuterium isotope effects in the reduction of a graded series of ketones by NaBH, and NaBD, have been measured. These effects are inverse, and show no systematic dependence on the degree of steric hindrance of the ketone. This evidence appears to invalidate the steric approach control-product development control explanation of the axial to equatorial product ratios (1). The primary isotope effect is very small, which is consistent with an early transition state in these reductions, as demanded by other explanations of product ratios, but since several other factors causing small isotope effects may be applicable, the evidence does not constitute proof of an early transition state.The main conclusions of this work have already been published in preliminary form (2).Les notions de "steric approach control" et 'kroduct deuelopment control" en relation avec le degri. de liaison dans I'ttat de transition, sont precisees. Les effets isotopiques du deuterium sur la cinbtique de reduction d'une serie de cetones par NaBH, et NaBD,, ont Ct C mesurts. Ces effets sont inverses et ne montrent aucune dependance systematique avec le degrt d'empschement sttrique de la cCtone. Cette mise en evidence montre que I'explication des rapports du produit axial et equatorial par le "steric approach control" et "product development control", n'est pas valable (1). L'effet isotopique primaire, trts faible, est compatible avec un debut d'6tat de transition dans ces rbductions. Ce rbsultat, deji mentionnt dans d'autres etudes, ne constitue pas une preuve puisque de nombreux autres facteurs peuvent Etre la cause de ces faibles effets isotopiques. Les conclusions principales de ce travail ont deja Ct C publikes dans une note preliminaire (2).

show abstract

Section: Kinetic Method4supporting

confidence: 80%

Section: Kinetic Method4mentioning

confidence: 92%

Section: Kinetic Method4mentioning

confidence: 99%

Section: The Terms Steric Approach Control Andmentioning

confidence: 99%

See 2 more Smart Citations

Deuterium Isotope Effects in the Reduction of Cyclohexanones. The Concepts of Steric Approach Control and Product Development Control

Wigfield¹,

Phelps²

1972

Can. J. Chem.

View full text Add to dashboard Cite

show abstract

“…The halftime of delivery of the pipette was taker1 as the time of samplir~g. Sulphuric acid (10 ml., 2 N) was added and the liberated iodine titrated with 0.1 N sodium thiosulphate using starch as indicator (9). The rate constants were calculated from a second-order rate plot and straight line graphs were obtained up to goy0 reaction.…”

Section: Methodsmentioning

confidence: 99%

Reactivity Studies on Natural Products: V. Rates of Borohydride Reduction of Some Ring a and B Steroid Ketones

Wheeler¹,

Mateos²

1958

Can. J. Chem.

View full text Add to dashboard Cite

The rates of reduction of 3-, 6-, and 7-cholestanone, coprostan-3-one, A'-and As-cholesten-3-one, and ~~('")-ergosten-3-011e with sodium borohydride in isopropanol have been measured. The proportions of a-and 8-isomers formed were determined in most cases and the corresponding rates of equatorial and axial reduction obtained. A4-Cholesten-3-one and 6-and 7-cholestanone are reduced a t a slower rate and AS-cholesten-3-one and ~~(l"-ergosten-3-one a t a higher rate than the saturated 3-ketosteroids.

show abstract

The Aldol Condensation

Nielsen

Houlihan²

2011

Organic Reactions

View full text Add to dashboard Cite

The aldol condensation takes its name from aldol (3‐hydroxybutanal) a name introduced by Wurtz who first prepared the beta‐hydroxy aldehyde from acetaldehdye in 1872. The aldol condensation includes reactions producing beta‐hydroxy aldehydes or beta‐hydroxy ketones by self condensations or mixed condensations of aldehydes and ketones as well as reactions leading to alpha, beta‐unsaturated aldehydes or alpha,beta‐unsaturated ketones formed by dehydration of intermediate beta‐aldols or beta‐ketals. The Claisen‐Schmidt condensation is most often taken to be the condensation of an aromatic aldehyde or ketone usually in the presence of a basic catalyst. The term aldol condensation has also been applied to many other condensations involving the reaction of an aldehyde or ketone. These condenations are discussed. The present review includes examples that are solely condensation reactions of aldehydes and ketones.

show abstract

Chemical effects of steric strains—XIII

Cited by 90 publications

References 9 publications

Deuterium Isotope Effects in the Reduction of Cyclohexanones. The Concepts of Steric Approach Control and Product Development Control

Deuterium Isotope Effects in the Reduction of Cyclohexanones. The Concepts of Steric Approach Control and Product Development Control

Reactivity Studies on Natural Products: V. Rates of Borohydride Reduction of Some Ring a and B Steroid Ketones

The Aldol Condensation

Contact Info

Product

Resources

About