Insulation phenomena of compressed air

McConnell, L. D.

doi:10.1109/ee.1957.6442812

Electr. Eng.

1957

DOI: 10.1109/ee.1957.6442812

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Insulation phenomena of compressed air

L. D. McConnell

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1966

1967

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“…Measured on 1.25 % (by volume) solutions in cyclohexane with 0.3% benzene added as an internal standard. Shifts are in cps from benzene at 60 Me 5. F. Langenbucher, R. Mecke, and E. D. Schmidt, Amn., 669,11 (1963).…”

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Dependence of hyperconjugative spin-spin coupling upon electron demand

Ripka¹,

Applequist²

1967

J. Am. Chem. Soc.

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It is found that the geminal coupling constants of the methyl protons in a series of para-substituted toluenes are quite insensitive to the electron-withdrawing nature of the substituents, which range from an a carbanion to an a carbonium ion. The long-range coupling constants between the methyl and o-hydrogens are likewise insensitive to a similar range of substituents. It is concluded that hyperconjugation involving the methyl groups is not strongly dependent upon electron demand, unlike chemical Baker-Nathan effects, though the conclusion must be tempered with the reservation that the exact relationships between the magnitudes of the coupling constants and the magnitude of hyperconjugative stabilization are not yet known.A common but imperfectly understood chemical observation is the Baker-Nathan reactivity order, in which alkyl groups appear to become better electrondonating groups as the number of «-hydrogens is increased.1 11•2 Thus, the Baker-Nathan order of electron release is Me > -Bu, the opposite of the accepted inductive order. It is commonly but by no means universally found that the Baker-Nathan order prevails in situations of large electron demand upon the alkyl group, while the inductive order is found where the electron demand is small.1•2 The Baker-Nathan effect is frequently explained as due to carbon-hydrogen hyperconjugation, which it is supposed should increase as electron demand increases.1 Another school of thought holds that the Baker-Nathan effect is a steric effect, usually involving solvent.2An entirely different manifestation of carbonhydrogen hyperconjugation is found in certain nuclear spin-spin coupling constants. It now seems well established that the long-range coupling constants between an aromatic methyl group and the ring protons arise primarily through a 7r-coupling mechanism, i.e., through carbon-hydrogen hyperconjugation.3-11 It is also now evident that the geminal coupling constants of methyl or methylene protons are enhanced (i.e., given larger negative values) by adjacent 7r-electron systems, and that such enhancement has the geometric dependence expected if hyperconjugation were involved and is opposite in sign to the effect produced by substituents which withdraw electrons inductively.12-17 A molecular orbital study by Pople and Bothner-By17 predicts (1) E. Berliner, Tetrahedron, 5, 202 (1959).

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Dependence of hyperconjugative spin-spin coupling upon electron demand

Ripka¹,

Applequist²

1967

J. Am. Chem. Soc.

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Electric Strength of Compressed Air in a Uniform Field

James¹,

Ryan²,

Powell³

1966

Nature

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Insulation phenomena of compressed air

Cited by 2 publications

References 0 publications

Dependence of hyperconjugative spin-spin coupling upon electron demand

Dependence of hyperconjugative spin-spin coupling upon electron demand

Electric Strength of Compressed Air in a Uniform Field

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