Ethane interaction diagram

The ethane molecule can be constructed by union of two pyramidal methyl radical fragments. The interaction diagram is shown in Fig. 16 and the key stabilizing orbital interactions are depicted below. 

Fig. 7.4 Molecular oribital interaction in ethane, and their interaction diagram emphasising the stabill sation by C—H hyperconjugation.

As usual, we can tackle the problem with or without using the concept of hybridisation. The C—X bond in a molecule such as methyl chloride, like the C C bond in ethane, has several orbitals contributing to the force which keeps the two atoms bonded to each other but, just as we could abstract one pair of atomic orbitals of ethane and make a typical interaction diagram for it, so can we now take the corresponding pair of orbitals from the set making up a C—Cl a bond. 

Lcl us consider A2II6 as a dimerization product of two AH3 units. 10.11 shows the least-motion approach of two CH3 radicals to form ethane C2H6. The MO correlation-interaction diagram in 10.12 shows that, given conservation of symmetry, the occupied MOs of two -CH3 radicals lead only to those of the ground state of ethane. Hence 10.11 is a symmetry-allowed reaction. If dimerization of... 

PROBLEM 2.13 Use an orbital interaction diagram like the one for Hej in Rgure 1.46, p. 40, to show the destabiUzation in eclipsed ethane. How many eclipsing filled orbital-filled orbital interactions are present ... 

PROBLEM 2.14 There is a related orbital effect that stabili%es staggered ethane. Use an orbital interaction diagram like the one for H2 in Rgure 1.47, p. 42, to show the stabilization in staggered ethane. This problem is much harder than Problem 2.13, so here is some help in the form of a set of tasks. The explanation that this problem leads to was first pointed out to MJ by an undergraduate just like you about 25 years ago. 

FIGURE 2.23 An orbital interaction diagram for the formation of ethane through the combination of a pair of methyl radicals. 

Data at two temperatures were obtained from Zeck and Knapp (1986) for the nitrogen-ethane system. The implicit LS estimates of the binary interaction parameters are ka=0, kb=0, kc=0 and kd=0.0460. The standard deviation of kd was found to be equai to 0.0040. The vapor liquid phase equilibrium was computed and the fit was found to be excellent (Englezos et al. 1993). Subsequently, implicit ML calculations were performed and a parameter value of kd=0.0493 with a standard deviation equal to 0.0070 was computed. Figure 14.2 shows the experimental phase diagram as well as the calculated one using the implicit ML parameter estimate. 

Figure 3.28 shows the P-T diagram for four polyethylene-low molecular weight hydrocarbon mixtures. The cloud point pressures decrease substantially with increasing carbon number, or conversely polarizability, as a result of increased dispersion interactions between polyethylene and the solvent. Free volume differences between polyethylene and the hydrocarbons also decrease as the carbon number is increased. Even though ethane and ethylene have virtually identical polarizabilities, the cloud point curve with ethane is at a much lower pressure than that with ethylene, since the quadrupole moment of ethylene enhances ethylene-ethylene interactions relative to ethylene-polyethylene interactions because polyethylene is a nonpolar polymer. The two cloud point curves for polyethylene with propane and propylene are virtually identical. Evidently, the quadrupole moment for propylene is weak enough that propylene-propylene polar interactions do not substantially influence the strong dispersion interactions between polyethylene and each of these two solvents of virtually identical polarizabilities. 

Vq can be taken as being equal to the ethane barrier (2.S-2.9 kcal/mol). The potential energy diagram for rotation about the C-C bond of ethane is given in Fig. 3.1. The ethane barrier may be taken as a standard rotational barrier for acyclic hydrocarbons when analyzing the contribution of torsional strain to the total steric strain. The stereoelectronic origin of the ethane barrier was discussed in Chapter 1. Any steric interactions which are present in more highly substituted systems will make an additional contribution to the barrier." ... 

The diagram tJmws only the interaction with the energy state of ethane [Pg.89]

Figure 8 Three-dimensional PNBO overlap diagrams depicting hyperconjugative interactions for the in-plane ng - interaction of formaldehyde (left) and the vicinal antiperiplanar ctch - crcw interaction of ethane (right), both at RHF/6-311G level...

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