Single-bond molecules, geometry

Compare the geometries of triplet and ground state singlet anthrone. Where do they differ the most Focus on the carbonyl group. Has the CO bond distance altered Does the molecule incorporate a fully-developed CO n bond (as in ground state singlet anthrone), or a single bond (as in phenol) Is the carbonyl carbon planar or puckered Rationalize your observations. 

In Section 7.2, we saw that insofar as geometry is concerned, a multiple bond acts as if it were a single bond. In other words, the extra electron pairs in a double or triple bond have no effect on the geometry of the molecule. This behavior is related to hybridization. The extra electron pairs in a multiple bond (one pair in a double bond, two pairs in a triple bond) are not located in hybrid orbitals. 

In 1940 Sidgwick and Powell surveyed the geometry of the singly bonded AX molecules whose structures were known at the time and showed that most of them could be ra-... 

An interesting application of these principles is the prediction of CO dissociation routes on the closed-packed (111) surface of rhodium (see Fig. A.17). Two factors determine how the dissociation of a single CO molecule proceeds. First, the geometry of the final situation must be energetically more favorable than that of the initial one. This condition excludes final configurations with the C and the O atom on adjacent Rh atoms, because this would lead to serious repulsion between the C and O atoms. A favorable situation is the one sketched in Fig. A.17, where initially CO occupies a threefold hollow site, and after dissociation C and O are in opposite threefold sites. The second requirement for rupture of the CO molecule is that the C-0 bond is effectively weakened by the interaction with the metal. This is achieved when the C-O bond stretches across the central Rh atom. In this case there is optimum overlap between the d-electrons of Rh in orbitals, which extend vertically above the surface, and the empty antibonding orbitals of the CO molecule. Hence, the dissociation of CO requires a so-called catalytic ensemble of at least 5 Rh atoms [8,21,22]. 

When EO is formed, single bonds from two adjacent carbons are connected to an oxygen atom. A three-member ring is always in a strained condition, due to the geometry of the molecule. Because of the propensity to relieve the strain, epoxides are very reactive. Practically all the EO produced is converted to chemical intermediates as a result of a ring opening reaction. 

The test set used for most comparisons in the present paper is Database/3 18), which was introduced elsewhere. It consists of 109 atomization energies (AEs), 44 forward and reverse reaction barrier heights (BHs) of 22 reactions, 13 electron affinities (EAs), and 13 ionization potentials (IPs). There are a total of 513 bonds among the 109 molecules used for AEs, where double or triple bonds are only counted as a single bond. Note that all ionization potentials and electron affinities are adiabatic (not vertical), i.e., the geometry is optimized for the ions... 

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