Ethyl group orbitals

Cations are by no means the only species where the effects of hyperconjugative delocalization reveal themselves in such a striking manner. Similar effects exist in neutral systems or in anions. For instance, the normal propyl anion should tend to be eclipsed (E) since in this manner the molecule would optimize the 4-electron interactions between the ethyl group t orbital and the p orbital which carries the electron pair. In the bisected conformation, where ttchs and ttchs have both been raised in energy, the four-electron, destabilizing (see Section 1.7, rule 2) p ->7r interaction is stronger than in the eclipsed conformation. At the same time the two-electron, stabilizing p ->ir interaction is weaker than in the eclipsed conformation. Both effects favor the eclipsed conformation. 

The dipolar parts of the analyzed hfs tensors have been compared with calculated values obtained from first order expressions of the electron-nuclear dipole interaction (5.3)57. The coefficients of the atomic orbitals used in this computation, which considers all two- and three-center contributions, are obtained from an extended Huckel calculation (ethyl groups replaced by protons). It has been found that almost 100% of the unpaired electron is located on the CuS4 fragment so that the replacement of the ethyl groups by protons is of minor importance for the calculation of the atomic orbital coefficients. The experimental and theoretical hfs data, summarized in Table 8, are found to... 

The active catalyst formed then has an octahedral structure, with the four Cl attached to the latice and the ethyl group attached to the Ti through a s bond, and leaving a vacant orbital at the position where originally the fifth chlorine was attached. Once the active catalyst is formed, the monomer is attracted towards the vacant d-orbital which then forms a transition p complex with the Ti, as shown below ... 

The transition state quickly give rise to the growth of the Polymer chain by the monomeric insertion at the Ti-Et bond. While the monomeric group is inserted and the chain grows, the vacant ethyl group was originally attached ... 

The introduction of -alkyl substituents to the secondary amine donors of the macrocycle results in anodic shifts in both oxidation and reduction potentials of the complexes relative to the parent ligand systems (Table II). The extent of anodic shifts depends on the number of alkyl groups introduced to the ligand (47,55a). That is, -alkylation makes the attainment of the Ni(I) state easier and the Ni(III) state more difficult. The stabilization of Ni(I) species by -alkylation is ascribed to solvation and stereochemical effects (55b, 60). -Ethyl groups have greater inductive effects than -methyl groups and yield less anodic shift in both oxidation and reduction potentials (47). This anodic shift of redox potentials may be attributed to weaker Ni-N interactions in the -alkylated complexes. The weaker Ni-N interaction for the tertiary amine results in the stabilization of antibonding o--orbitals of the Ni(II) complex, which makes it more favorable to add an electron, but less favorable to remove an electron. 

It is surprising that the ethyl group is located on N-3 of the thiatriazolium salts. Comparison with other multisite heterocycles for which the relative nitrogen nucleophilicity is known suggested the reactivity order N-4 > N-3 > N-2.6 The authors attempted to derive a reactivity rationale for the assignment from self-consistent field (SCF)-MO-CNDO calculations. Total charge densities and the frontier orbital... 

The approach given above can be extended to propanal and methyl vinyl ether. For propanal, we use the frontier orbitals of an ethyl group in place of 7tMe and 7i Me and refer back to Figure 7.2. For methyl vinyl ether, we replace 7tMe and 7i Me by the frontier orbitals of OMe, and 7tco and n co by 7tcc and jtcc. 

The ethyl group can be built by combining the orbitals of the methyl (Figure 7.1) and methylene (Figure 7.3) groups. Its HOMO is an out-of-phase combination of the CH3 and CH2 HOMOs, whereas its LUMO is an in-phase combination of the fragments LUMOs (cf. p. 152) ... 

In all cases it appeared that the migrating group D in equation (76) should possess a p-77-orbital, and migration of methyl and ethyl groups has not been observed in the amide series. 

Step 1 A titaninm halide and an ethylaluminum compound combine to place an ethyl group on titanium, giving the active catalyst. Titaninm has one or more vacant coordination sites, shown here as an empty orbital. 

Whangbo and Wolfe (251), in the case of 127, considered the highest occupied orbitals of the ethyl group as a whole, namely ffcc and instead of orbitals of a substituted methylene group (Figure 28, cf. Figure 27). The energies of orbitals Ucc and are nearly the same and from this point... 

Figure 20. Model of heme A with the farnesyl ethyl group in a conformation that allows pi-orbital overlap between adjacent double bonds and between the porphyrin and the C -Cg bond...

The ethyl cation is the prototype system for demonstrating the effect of hyperconjugation. Consider classical CH3CH2 as a combination of a methyl group and a -CH2 centre. The group orbitals of the methyl group (equivalent to the MOs of NH3) include the 7CcH3-orbital shown schemat-... 

The structure of the relevant carbocation is shown at the right. Approach of a nucleophile toward the top lobe of its p orbital is partly blocked by the ethyl group two carbon atoms over and to a lesser extent by the ester function one carbon farther away (green). In addition, the hydroxy group on the bottom face of the ring directs nucleophilic addition of a water molecule from below by hydrogen bonding, as shown. 

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