MO bond order

Exercise Determine the formal MO bond orders WM0), bc(M0), and b c AO) for the general (cuAB C)2(cuA BC)2 hyperbonded electron configuration. 

Exercise For what ionicity tAB is the maximum MO bond order b wMO] obtained How does this maximum value compare with that of the Pimentel MO description ... 

Note that the two electrons (one from each hydrogen atom) have both gone into the sigma bonding MO. We can determine the bonding situation in MO theory by calculating the MO bond order. The MO bond order is the number... 

Figure 1 PPP-SCF-MO bond orders and charge densities for 1,4-dioxin and 1,4-dithiin <70BCJ3929)...

We would also like to mention here another important point. Since the Hiickel and topological matrices are closely related for a particular conjugated molecule, all properties of a molecule (i.e. energy, MOs, bond orders, charge densities) which may be derived from the topological matrix by mathematical treatment must be dependent on the molecular topology 23>. This may be one reason why the predictive power of elementary Hiickel theory is in many cases (e.g. for alternant hydrocarbons) as good as that of any more elaborate approach 58>. 

Population of e(xz,yz) n orbitals in tetragonal oxo-metal complexes reduces the MO bond order. Although triple bonding is assured in d° and d1 complexes, the... 

Fig. 2 Correlation of MO bond order with 4-electron count in oxo-metal complexes. The gray shaded region corresponds to a 7t bond order of 0.5 the oxo ligands in these complexes are expected to be extremely basic...

In tetragonal traws-dioxometal complexes with 0, 1, or 2 -electrons, 4 bonds (two a and two ji) will be divided between two MO interactions. The average MO bond order is two, such that a double bond representation is not incorrect, although a structure with one full bond and two half bonds is a more accurate depiction of the interaction. 

Compound or ion Mo—Mo bond distance / pm Mo-Mo bond order Notes... 

Alternatively, recourse may be made to the average excitation energy approximation, in which the several triplet excitation energies are replaced by an average value AE. The coupling is then given in terms of P spSm total MO bond order between the s... 

MO theory redefines bond order. In a Lewis structure, bond order is the number of electron pairs per linkage. The MO bond order is the number of electrons in bonding MOs minus the number in antibonding MOs, divided by two ... 

MO bond order One-half the difference between the numbers of electrons in bonding and antibonding MOs. (336) model (also theory) A simplified conceptual picture based on experiment that explains how an aspect of nature occurs. (9) molality (m) A concentration term expressed as number of moles of solute dissolved in 1000 g (I kg) of solvent. (403) molar heat capacity (C) The quantity of heat required to change the temperature of I mol of a substance by 1 K. (187) molar mass [M) (also gram-molecular weight) The mass of 1 mol of entities (atoms, molecules, or formula units) of a substance, in units ofg/mol. (72)... 

Several M02 complexes have been investigated by MoNMR spectroscopy. " The resonances are broad (vj = 320-1440 Hz) and the chemical shifts (2900 to 4200p.p.m. relative to [MoOJ " at Op.p.m.) correspond to the lowest observed shielding of the Mo nucleus this is consistent with the extent of Mo shielding decreasing steadily with an increase in Mo— Mo bond order. 

Mason and Grieves reported measurements for both mononuclear and dinuclear Mo(II) compounds. The chemical shifts for [Mo2X4(PMe3)4] (X = Cl, Br, I) show a normal halogen dependence and, for all the dinuclear species, shielding increases with the Mo-Mo bond order as quadruple < triple < double < single bond, which they note is opposite to the sequence for NMR. 

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