Ethylene interaction diagram

Fig. 1. Orbital interaction diagram for the formation of thiirane through interaction of ethylene and sulfur...

Qualitatively, the interaction diagram would closely resemble that in Fig. 3, since electron-donating substituents in both addends would raise the molecular levels of both the carbonyl compound and the olefin. Only the energy gap, E(n)-> F(n), would increase, the net result being that the calculated ratio of concerted to biradical reaction, Eqs. 40 and 41, should be even closer to unity than in the formaldehyde-ethylene case. Detailed calculations 38> support this conclusion, so PMO theory predicts that the overall stereochemical results are due to a combination of concerted (singlet) and biradical (triplet) mechanisms. This explanation agrees with the experimental facts, and it bypasses the necessity to postulate differential rates of rotation and closure for different kinds of biradical intermediates. 

The regioselectivity of each one of the previously cited reactions, Eqs. 29—31, is well-correlated by the interaction diagram. The degenerate interaction of the bonding levels is controlling, and whether the reaction is concerted or biradical the major orientation should be as shown in 19. The olefin 1,1-dichloroethylene was taken as the model for 1,1-dimethoxy-ethylene. 

We first consider the union of the ethylenic fragments A and B in a cis and trans geometry. The interaction diagrams for these unions are shown in Fig. 3. We distinguish two types of interactions ... 

We now proceed to the next case in which the substituents consist of a donor and acceptor. The specific molecule will be 1,2-difluoro-dicyanoethylene. Following the previous procedure, the group MO s of the substituents and the ethylene -n and 7r MO s are used to construct the MO s of the composite system. The interaction diagrams are shown in Fig. 25. The results are analogous to the previous example except for the additional stabilizing interactions which will also favor the cis isomer. Consequently, the cis isomer is expected to be the most stable isomer. 

Fig. 56. Configuration interaction diagram for (a) 1,1-difluoroethylene and (b) 1,2-difluoro-ethylene. and n2 are sigma charge resonance configurations. Similarly, ZI3 and r14 are pi charge resonance configurations...

Figure 2.38. Schematic orbital interaction diagram illustrating the interaction of the ethylene lb2u ( ) (left side) and lb3g ( ) (right side) orbitals with the metal d-band where the rf-band center of Cu lies at higher binding energy than that of Ni. From Ref. [85].

Figure 5.1. (a) SHMO results for ethylene, (b) The interaction diagram for ethylene note that Asl = Asu because overlap is assumed to be zero in SHMO theory. 

The SHMO calculation on ethylene yields the results shown in Figure 5.1a. The n and 7 orbitals are precisely one ft unit above and below a. The SHMO results are presented in Figure 5.16 in the form of an interaction diagram. In this case, and are assigned the same value, namely 1 / , in the spirit of SHMO theory, but we know that the effect of proper inclusion of overlap would yield > A l-... 

Figure 11.7. Interaction diagrams comparing (a) ethylene to (b) benzyne. Note that (i I < lAxl-The aromatic n system is largely unperturbed with nearly degenerate orbitals at a — /icc and a + Pcc -...

Answer to 9 and 10. The orbital interaction diagram for the bonding is shown in Figure B3.8. The geometric changes described for ethylene, its cation radical, and its excited state reinforce our conclusions regarding the elfect of overlap, namely that... 

Figure B3.8. Interaction diagrams (a) between 2p orbital with the antisymmetric group orbital of the adjacent CH2 group (b) of n orbitals ethylene in its ground state (c) of twisted ethylene cation (1d) of the n-n state of ethylene.

Reaction of alkenes with BrCl proceeds via the intermediate [alkene-Br]+ rather than the intermediate [alkene-Cl]+. Explain using a two-orbital interaction diagram. (The structure of the complex between ethylene and BrCl in the gas phase has been determined by microwave spectroscopy. It is T-shaped, with the BrCl molecule lying perpendicular to the ethylene plane and pointing bromine-end first toward the midpoint of the C=C bond Legon, A. C. Bloemink, H. I. Hinds, K. Thorn, J. C., Chem. Eng. News, 1994 Nov. 7, 26-29.)... 

Use an orbital interaction diagram to explain the observation that tetracyano-ethylene is very easily reduced to its radical anion. 

Diels-Alder reaction, 169-170 aromatic TS, 151 benzyne, 160 butadiene + ethylene, 169 diastereoselectivity, 292 interaction diagram, 169 orbital analysis, 169-170 orbital correlation diagram, 198, 201 reverse demand, 169 substituent effects, 169-170 Diethyl tartrate, 11 Difluorocarbene ( CF2), 115... 

The atomic numbering scheme is given in (c). The ethylene MOs are denoted by k and n and those of butadiene and fulvene by and Tt, respectively. Orbitals 2 and 4 are antisymmetric with respect to the fulvene symmetry plane, whereas n, n, 4 and 3 are symmetrical. Consequently, the last four orbitals can interact during the union of the fragments, but the 2 and 4 orbitals will remain unchanged. The interaction diagram is shown below. 

The chemical bonding of re coordinated ethylene is very similar to the Chatt-Dewar-Duncanson picture of CO coordination (Fig. 4.6). The donating orbital is the doubly occupied n orbital that is a-symmetric with respect to the normal to the surface. When adsorbed atop it interacts with the highly occupied dz2 surface atomic orbital and the partially filled s and pz orbitals. The ethylene LUMO is the empty asymmetric n orbital, which interacts with the surface dxz and px orbitals. The corresponding overall interaction is relatively weak and no hybridization on ethylene is assumed to occur. The orbital interaction diagram of the occupied ethylene n orbital with surface atom dz2 orbital is analogous to that sketched for the CO 5a orbital in Fig. 4.4. When this dz2 becomes nearly completely occupied, as occurs, for instance, for Pd or Pt, the ethylene-rc surface atom dz2 interaction... 

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