Resonance hyperconjugation and

Rank primary, secondary, tertiary, and ally lie radicals in order of decreasing stability. Do the same for the corresponding carboca-tions. Do the results indicate something about the relative ability of hyperconjugation and resonance to stabilize radical and cationic centers ... 

The electronic effects of cycloalkyl annelation can be divided into inductive and resonance effects. Few measurements of the resonance contributions of cycloalkyl substituents exist. A single determination of the resonance parameter para to substitution in o-xylene, tetralin and indan suggests that hyperconjugative release is fairly constant within a series of benzocycloalkenes, and that strain induced electronic effects must act inductively. ... 

Support for hyperconjugation as the major cause of p isotope effects is the fact that the effect is greatest when D is anti to the leaving group (because of the requirement that all atoms in a resonance system be coplanar, planarity of the D—C—C—X system would most greatly increase the hyperconjugation), and the fact that secondary isotope effects can be transmitted through unsaturated systems. There is evidence that at least some p isotope effects are steric in... 

Traditionally, the focus has been on polar and resonance effects, based on VB ideas about structure, and the emphasis is on partial charges arising from polar bonds and resonance/hyperconjugation. However, in MO theory, we use the idea of perturbations. The question asked is, How does a substituent affect the energy and shapes of the orbitals, with particular attention to the HOMO and LUMO, the frontier orbitals. Ultimately, substituents affect structure and reactivity by changing the electron density distribution. From the concept of electronegativity, we know that bonds have dipoles,... 

The relative stabilities of 3 > 2 > 1 are explained through hyperconjugation and by the number of resonance contributing structures, t-butyl cation has nine contributing structures 2-butyl cation has five contributing structures n-butyl cation has two contributing structures. 

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