Overlap constructive

Dimethylborane+propene Cl depicts the transition state for addition of dimethylborane onto the terminal alkene carbon of propene. Examine and describe the vibration with the imaginary frequency. Which bonds stretch and compress the most What simultaneous changes in bonding are implied by these motions Simultaneously display the highest-occupied molecular orbital (HOMO) of propene and the lowest-unoccupied molecular orbital (LUMO) of dimethylborane. Is the overall geometry of the transition state consistent with constructive overlap between the two Explain. 

Fig. 9 illustrates that the two acetylenic systems become nearly parallel at C1-C6 distances close to 3 A where the constructive overlap of the re-orbital with one of the re -nodes is compensated by a destructive overlap with the other rc -node (Fig. 9, bottom). From a conceptual point of view, the properties of the in-plane re-system at the 3 A threshold bear a striking resemblance to the interaction of the two re-bonds in D2h cyclobutadiene where the re-re interaction is zero and the re-re repulsion is considerable, thus accounting for the extreme instability of this antiaromatic molecule.41 Even more relevant is a comparison with the TS of the symmetry forbidden thermal [2S + 2S] cycloaddition (Fig. 10) which prompted us to call this region antiaromatic .42... 

Factor analyses of the PCL-R (e.g., Hare, 1991) identified two underlying factors interpersonal-affective (Factor 1, including such traits as callous ) and antisocial behavior (Factor 2, e.g., juvenile delinquency ). The interpersonal-affective features are generally considered to be central to the construct (e.g., Harpur, Hart, Hare, 1994). It is important to note that a similar construct is included in the DSM—antisocial personality disorder— but it is defined primarily in behavioral terms and does not match many of the nonbehavioral aspects of Cleckley s description. Moreover, both constructs overlap substantially with the concept of criminality, but they are not isomorphic with it. An individual can be a psychopath and can still be successful and without a criminal record. 

In the pi bonding molecular orbital of ethylene, the lobes that overlap in the bonding region between the nuclei are in phase that is, they have the same sign (+ overlaps with +, and — overlaps with —). We call this reinforcement constructive overlap. Constructive overlap is an important feature of all bonding molecular orbitals. 

An overlap of orbitals that contributes to bonding. Overlap of lobes with similar phases (+ phase with + phase, or — phase with — phase) is generally constructive overlap, (p. 671)... 

The lowest-energy molecular orbital is entirely bonding, with constructive overlap between all pairs of adjacent p orbitals. There are no vertical nodes in this lowest-lying MO. 

A third factor is the symmetry of the orbitals—two atomic orbitals must have the appropriate symmetry to combine. Thus a 2p. orbital cannot combine with a 2p or 2pz orbital since they are all perpendicular to each other (they are orthogonal). In one case the two p orbitals have no overlap at all in the other case any constructive overlap is cancelled out by equal amounts of destructive... 

Although the state correlation diagram is physically more meaningful than the orbital correlation diagram, usually the latter is used because of its simplicity. This is similar to the kind of approximation made when the electronic wave function is replaced by the products of one-electron wave functions in MO theory. The physical basis for the rule that only orbitals of the same symmetry can correlate is that only in this case can constructive overlap occur. This again has its analogy in the construction of molecular orbitals. The physical basis for the noncrossing rule is electron repulsion. It is important that this applies to orbitals—or states—of the same symmetry only. Orbitals of different symmetry cannot interact anyway, so their correlation lines are allowed to cross. 

FIGURE 8.34 tt bonding between a metal d y orbital and four ligand tt orbitals with phases chosen for maximum constructive overlap. 

Seven orbital combinations (n + 1) lead to bonding interactions within the B6 core these are shown in Figure 13-10. Constructive overlap of all six hybrid orbitals at the center of the octahedron yields one framework bonding orbital, labeled /l,.17 Additional bonding interactions are of two types overlap of two sp hybrid orbitals with parallel p orbitals on four boron atoms (three such interactions, symmetry label and overlap of p orbitals on four boron atoms within the same plane (three interactions, symmetry label t2 )- The remaining orbitals form antibonding molecular orbitals or are nonbonding. A summary follows. 

The pi molecular orbitals of ethylene. The pi bonding orbital of ethylene is formed by constructive overlap of unhybridized p orbitals on the xp"-hybrid carbon atoms. Destructive overlap of these two orbitals forms the antibonding pi orbital Combination of twop orbitals must give exaaly two molecular orbitals. 

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