Conjugative interaction

These and other studies of the relative substituent effects of X and CH X in nitration were considered in terms of the transmission factor a of the methylene group. To avoid complications from conjugative interactions, attention was focussed mainly on substitution at the meta-position, and ct was defined in terms of partial rate factors by the equation ... 

A comparison of 190 with 1,3-dioxane 177 shows that the anomeric interactions in 177 are much stronger than in 190. Moreover, the balance of the computed hyper-conjugative interactions successfully accounts for the relative C—Ha and C—Hgq... 

However, the iodo-substituent, which might be expected to show similar behavior, is well behaved. The behavior of the substituents MeSO, SCF3, and CF3SO would be instructive in this connection, but no data exists for these substituents in any of the sets. The substituents NHCOMe and OCgHs, which involve competing conjugative interaction mechanisms, as well as coplanarity problems, are only moderately well behaved in the sets. Calculated values of vary from —.74 to -.86 for the former and -.74 to -.92 for the latter. There is, however, a considerable presumption in the case of the NHCOMe substituent that this behavior is solvent related. The value —.74 (reaction 6) is obtained in water solvent at 25°, and the value —.86 (reaction 23) is obtained in dimethylformamide solvent at 17°. The 0/j(ba) values calculated for the NHCOMe substituent show similar trends with solvent, as shown in Table XVI. 

As described for the corresponding polymers, a powerful strategy for arriving at soluble oligomers with maximum conjugative interaction is incorporation of the PPP backbone into a stepladder - or ladder (see Sect. 2.2.) - framework, in... 

The soluble products are able to form charged high-spin states after chemical and electrochemical oxidation. The high-spin character is the result of the lack of conjugative interaction between the highly distorted, orthogonally arranged aromatic subunits (decoupled rr-systems) [68]. 

The inductive and electrostatic effects, steric constraints and conjugative interactions are the major factors that determine the configurational stability of a-sulfonyl carbanions. These are thought to be pyramidal with appreciable electrostatic inhibition to racemization by way of inversion. LCAO-MO-SCF calculations have indicated the conformer 195 in which the lone pair is directed along the bisector of the OSO angle to be the most stable in acyclic sulfones. ... 

Information about inductive and conjugative interactions between C=C and C=0 moieties has been derived from photoelectron spectra of di-tert. butyl cyclopropenone and the corresponding cyclopropenone163a) and correlated with MINDO/2 calculations. 

Does the 10 kJmol 1 stabilization for adjacent exomethylene groups in cyclobutane arise from conjugative interactions Is the 5 kJmol-1 destabilization for nonadjacent exomethylenes in cyclobutane general for other cycloalkane derivatives ... 

The parent triafulvene, 104, is the sole representative of this hydrocarbon class for which there is a suggested enthalpy of formation75, namely 423 kJ mol 1. If the conjugative interactions of the exo-methylene with cyclopropene and cyclopentadiene were the same, then equation 39 would be thermoneutral. 

See, for example, R. S. Hosmane and J. F. Liebman, Tetrahedron Lett., 33, 2303 (1992). We additionally note that in the absence of any conjugative interaction, the difference of the enthalpies of formation of fulvene (vide infra) and benzene would very nearly equal the difference of the enthalpies of formation of methylenecyclopentane and cyclohexene. The former difference is 161 kJ mol-1 while the latter difference is but 17 kJ mol-1. 

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