Linear configuration

Triple bonds are formed by the sharing of three pairs of electrons to form a a and two n bonds. Spatially these three bonds behave as a single bond. Consequently acetylene (ethyne) C2H2 has the linear configuration often represented as H—C=C—H. 

L == Me3N, py, etc. X = I, Br, Cl, CN) feature a linear configuration as expected from the involvement of the Ou antibonding orbital of IX (Fig. 17.3a, b, c). When the ligand has two donor atoms (as in dioxan) or the donor atom has more than one lone-pair of electrons (as in acetone) the complexes can associate... 

There have a number of computational studies of hypothetical RMMR species [10-13, 40, 411. The simplest compounds are the hydrides HMMH. Some calculated structural parameters and energies of the linear and trans-bent metal-metal bonded forms of the hydrides are given in Table 1. It can be seen that in each case the frans-bent structure is lower in energy than the linear configuration. However, these structures represent stationary points on the potential energy surface, and are not the most stable forms. There also exist mono-bridged, vinylidene or doubly bridged isomers as shown in Fig. 2... 

Another type of linear configuration known as bow-tie is shown in Figure 10.10. The actuator is constmcted using dielectric elastomer film having the shape of a bow-tie with two compliant electrodes configured on its two surfaces. Application of the electric field results in planar actuation which because of the bow-tie shape is translated into linear motion. Typical applications of these types of actuators comprise a hexapod robot, to mimic the motion of insects like walking, to manufacture various animated devices like face, eyes, skin, etc., or the design of micro-air vehicle/omithopter. 

In general three position variables will be needed to specify the potential energy of the reaction system. These may be the X-Y, Y-Z, and X-Z internuclear distances or two internuclear distances and the included angle. Even in this relatively simple case, four dimensions would be required for generation of the potential energy surface. However, if we restrict our attention to linear configurations of these atoms, it is possible... 

Schematic representation of the potential energy of a system comprised of three atoms in a linear configuration as a function of the internuclear separation distances. The dashed line represents the reaction X + YZ — XY+ Z.

Aggregated helices helical configuration linear configuration ... 

Adsorbed nitriles are able to block CO from entering its linear configuration when the adsorption step is performed at 0.05 V(SHE). Adsorbed Sn atoms behave in a manner which supports previous models for their catalytic enhancement of CO oxidation rates. 

Under the present conditions, we propose that the -CN group in the nitrile molecules acts in a similar fashion. The nitrile molecules are adsorbed on a fraction of the Pt surface atoms, and their presence forces the co-adsorbed CO molecules on the remaining sites to assume the bridging configuration. When the potential is increased, part of the driving force for this conversion is removed and the CO molecules convert back to their linear configuration. This conversion is irreversible when the potential is lowered a second time. The reason for this irreversibility is uncertain and should be explored further. 

The fact that linear CO species are observed at 0.05 V in the absence of C.H.CN (cf. spectrum a) indicates that H.O molecules at the inner Helmholtz plane are not able to displace CO out of its linear configuration at the same potential. This may be due to a re-orientation of the adsorbed HjO as a function of potential, with the positive end of the molecular dipole becoming attracted to the surface as the electrode potential is made more negative. This would reduce the ability of the H O molecule to donate electron density from its oxygen atom, and would also Increase the ability of its hydrogen atoms to compete for accepting electron density from the metal. 

The VSEPR treatment is best approached by considering the ion as made up from three ions F + H+ + F. The central proton possesses no electrons until the ligand fluoride ions supply two each. The two pairs of electrons repel each other to give the observed linear configuration of the three atoms. The two pairs of electrons would occupy the Is and 2s orbitals of the hydrogen atom and, what with a considerable amount of interelectronic repulsion, would not lead to stability. 

Fig. 4.12 The normalized eigenvalues, , of the triatomic molecule AH2 as a function of the bond angle, 2/3, for the particular choice of normalized atomic energy level mismatch, 5 = 1. The symmetries of the eigenfunctions are also shown for the bent and linear configurations.

N3 ion has a linear configuration, and a possible electronic configuration for the acid, therefore, is... 

At the present time there have been few ab-initio calculations on polyatomic potential surfaces for which a claim of quantitative accuracy can be made. The classic example of the surface stands out in this field as a longstanding challenge to theoreticians, and the best calculations on this are thought to be within 12 kJ/mole of the exact surface overall, and better than 4 kJ/mole for linear configurations which encompass the transition state (73-75). 

The only unsatisfactory behaviour was for the linear configurations O—H—H for which the energy appears to be too low. 

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