| 释义 |
ˌhyperconjuˈgation Physical Chem.
[f. hyper- 1 b + conjugation.]
A direct interaction between the electrons of a methyl or substituted methyl group in a molecule and the electrons of an adjacent conjugated system, the former being attracted towards the latter.
1939R. S. Mulliken in Jrnl. Chem. Physics VII. 340/2 In the cyclic dienes..there is interaction between this [pair of electrons] and the unsaturation orbitals, resulting in what may be called ‘cyclic conjugation’. This phenomenon has been..discussed by Hückel, except for the case where A is CH2. For this case we may introduce the term ‘hyperconjugation’, meaning an additional conjugation beyond that ordinarily recognized. [Note] The term..was suggested by Professor W. G. Brown, as an improvement on the term ‘superconjugation’ at first used by the writer. 1949Q. Rev. III. 229 Delocalisation of this type is known as σ-hyperconjugation, and since σ electrons are relatively tightly bound, the resulting energy of delocalisation is likely to be very small. Consequently, σ-hyperconjugation is generally ignored. 1952Chem. & Engin. News 17 Nov. 4881/2 Hyperconjugation denotes resonance interaction by alkyl, and particularly methyl, substituents in systems exemplified by H3 ≡ {Car}{b1}{Car} = C {lar} → H+H2C = C{b1}C- . 1962M. J. S. Dewar Hyperconjugation i. 13 The evidence..for the importance of hyperconjugation is much less conclusive than has been commonly supposed. 1965Phillips & Williams Inorg. Chem. I. xi. 400 Hydrogen is also unable to act as a π-donor, except possibly to a small extent in groups of hydrogen atoms as in CH3, the so-called hyperconjugation effect.
Hence hyperˈconjugated ppl. a., exhibiting hyperconjugation.
1949Q. Rev. III. 233 The carbon–carbon distance in acetaldehyde is approximately 0·04 a. less than the normal value, and..the shortening has been attributed to hyperconjugated structures. 1959E. S. Gould Mechanism & Struct. Org. Chem. ii. 49 Hyperconjugated structures in which a shift of electron density..has left the C{b1}H bonds with partial no-bond character. |
