Electronic and steric effects on hindered rotation about phenyl–carbon bonds

Anderson, J. Edgar; Pearson, Harry; Rawson, D. I.

doi:10.1039/c39730000095

Cited by 13 publications

(12 citation statements)

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“…Thus, in 9-methyltriptycene derivatives (Anderson and Rawson, 1973;Nakamura et al, 1973) free-energy barriers up to 10.6 kcal/mol at room temperature have been found. In horse ferricyanomyoglobin, a rotational barrier of a hememethyl group with AH* = 14.8 f 1.8 kcal/mol and AS* = -2.…”

Section: ) Rotation Of the Hap Methyl Group In The Enzyme-bound Ketmentioning

confidence: 95%

Rabbit muscle aldolase catalyzed proton exchange of hydroxyacetone phosphate with solvent

Pratt¹

1977

Biochemistry

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Rabbit muscle aldolase catalyzes the exchange with solvent of all three methyl hydrogens of hydroxyacetone phosphate. Under saturating conditions, rates of the following processes have been measured: deuteration of hydroxyacetone phosphate in 2H2O (by an NMR method), tritiation of hydroxyacetone phosphate in H2O and 2H2O, and detritiation of tritiated hydroxyacetone phosphate in H2O and 2H2O. It is clear from these measurements (1) that there is no primary kinetic isotope effect and hence that hydrogen abstraction is not rate determining to the exchange and (2) that only one (as the closest integer) methyl hydrogen exchanges per turnover. The argument is made that these observations are mutually exclusive in terms of the accepted aldolase mechanism in the absence of further restrictions imposed by the enzyme. Possible restrictions are discussed.

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Section: ) Rotation Of the Hap Methyl Group In The Enzyme-bound Ketmentioning

confidence: 95%

Rabbit muscle aldolase catalyzed proton exchange of hydroxyacetone phosphate with solvent

Pratt¹

1977

Biochemistry

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“…The present nmr measurements are meant to probe further the idea (1)(2)(3) that hyperconjugation of the carbon-metal bond with the aromatic .rr electron system determines the conformational preference about the C,2-C, 3 bond in benzyltrimethyl X (X = Si, Ge, Sn, Pb). Such an origin for its conformational behaviour was not suggested for benzyltrimethylmethane (neopentylbenzene), where steric interactions presumably are dominant (4)(5)(6)(7).…”

Section: Introductionmentioning

confidence: 99%

“…A variety of neopentylbenzene derivatives have been investigated by dynamic nmr methods with a view to establishing the free energies of activation, AG*, for rotation about the Csl,2-Cse~ bonds (4)(5)(6)(7). For the parent compound the reorientation rate 1s too fast to measure by such methods.…”

Section: Introductionmentioning

confidence: 99%

An NMR study of steric and hyperconjugative barriers in benzyl X(CH₃)₃, X = C, Si, Ge, Sn, Pb

Schaefer¹,

Penner²,

Takeuchi³

et al. 1989

Can. J. Chem.

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The 1H nuclear magnetic resonance spectra and their analyses are reported for benzyltrimethyl X (X = C, Si, Ge, Sn, Pb) and for the 2,6-dichloro derivatives where X = Si, Ge, Sn, Pb. The steric barrier to rotation about the Csp2—Csp3bond for X = C, based on the long-range proton–proton coupling constant over six bonds, 6J(H,CH2), must be greater than 20 kJ/mol. Unexpectedly, 6J(H,CH2) implies that the barriers for X = Si, Ge, Sn, Pb have relatively minor steric components. If these barriers are dominated by hyperconjugative interactions of the C—X bond with the aromatic π system, then they are probably mainly twofold in nature. Furthermore, their magnitude is likely to be near 9.5 kJ/mol for X = Si, Ge, Sn and may be as high as 12 kJ/mol for X = Pb. Keywords: NMR, benzyl X(CH3)3, X = C, Si, Ge, Sn, Pb; NMR, conformations; NMR, hyperconjugation.

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“…Hawkins et al (1971) Hawkins et al (1971) Hawkins et al (1971) Hawkins et al (1971) Hawkins et al (1971) Hawkins et al (1971 Anderson and Pearson (1971a) Anderson and Pearson (1971a) Anderson and Pearson (1971b) Anderson and Pearson (1971b) Anderson and Pearson (1971b) Anderson and Pearson (1971b) Anderson and Pearson (1971b) Anderson and Pearson (1971b) Anderson and Pearson (1972a) Anderson and Pearson (1972a) Anderson and Pearson (1972a) Anderson and Pearson (1972b) Anderson and Pearson (1972b) Anderson and Pearson (1972b) Anderson and Pearson (1972b) Anderson and Pearson (1972b) Bushweller and Anderson (1972) Bushweller and Anderson (1972) Dix et al (1966) Rieker and Kessler (1969) Rieker and Kessler (1969) Rieker and Kessler (1969) ) Siddall and Stewart (1968a, 1969b Siddall and Stewart (1969b) Siddall and Stewart (1969b) Siddall and Stewart (1969b) Siddall and Stewart (1969b); Bartle et al (1970) Siddall and Stewart (1969b…”

Section: Referencementioning

confidence: 99%

Rotation about Single Bonds in Organic Molecules

Sternhell¹

1975

Dynamic Nuclear Magnetic Resonance Spectroscopy

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Electronic and steric effects on hindered rotation about phenyl–carbon bonds

Abstract: The effect of substituents on rotation about the phenyl-carbon bond in substituted toluenes is reported and discussed in terms of steric and electronic interactions.CONFORMATIONAL preferences about an sp3-sp2 bond have

Cited by 13 publications

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Rabbit muscle aldolase catalyzed proton exchange of hydroxyacetone phosphate with solvent

Rabbit muscle aldolase catalyzed proton exchange of hydroxyacetone phosphate with solvent

An NMR study of steric and hyperconjugative barriers in benzyl X(CH₃)₃, X = C, Si, Ge, Sn, Pb

Rotation about Single Bonds in Organic Molecules

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Electronic and steric effects on hindered rotation about phenyl–carbon bonds

Abstract: The effect of substituents on rotation about the phenyl-carbon bond in substituted toluenes is reported and discussed in terms of steric and electronic interactions.CONFORMATIONAL preferences about an sp3-sp2 bond have

Cited by 13 publications

References 0 publications

Rabbit muscle aldolase catalyzed proton exchange of hydroxyacetone phosphate with solvent

Rabbit muscle aldolase catalyzed proton exchange of hydroxyacetone phosphate with solvent

An NMR study of steric and hyperconjugative barriers in benzyl X(CH3)3, X = C, Si, Ge, Sn, Pb

Rotation about Single Bonds in Organic Molecules

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An NMR study of steric and hyperconjugative barriers in benzyl X(CH₃)₃, X = C, Si, Ge, Sn, Pb