T-bond order

Species Charge dA T Bond order (% ionic) Valency (% ionic) ... 

The most optimistic response to this situation is to claim that the force constant — t-bond order relationship is still valid, but that the reference points need to be changed V(CO)e itself is then a possible reference compound (76). The relationship can then only be quantified by using calculated orbital populations for the reference species, and can only be tested by more extended comparisons between calculated bond order and observed force constant. Precisely this test has been apphed to a whole group of substituted and unsubstituted octahedral carbonyls of groups VI and VII, the substituents in every case being hahde (77). The data used in fact were not force constants, but Cotton-Krainhanzel parameters this does not actually matter, since no reference molecules were used at all. Excellent agreement was found with an expression. 

From tabulated values of n-electron densities (t/,), bond orders [pij), atom-atom (Tti i), bond-bond (rcij.ij), and bond-atom polarizabilities (21, . ), X has been calculated. These values (Table I) resemble those obtained by direct solution of the Hiickel matrices. 

Covalen t radii for all th e clem cn ts are readily available an d the bond orders of all bonds arc available from the molecular graph. Prior to describing the explicit default parameter scheme, it is nee-... 

The very long 8-1 bonds in the linear 8-1-8 bridge (267.5 pm) are notable and have been interpreted in terms of an 8-1 bond order of f. Even weaker 8- T interactions occur in the cation [8214] + which could, indeed, alternatively be regarded as an 82 + cation coordinated side-on by two I2 molecules (Fig. 15.23). This... 

Under such circumstances, the E-X and X-Y bond distances should be strongly correlated in C.-T. spoke adducts. In fact, it is well known that for C.-T. spoke I2-adducts with S-donors a reciprocal correlation exists between (f(I-I) and rf(S-I), which was initially proposed by F.H. Herbstein and W. Schwotzer as a hyperbola.46 Assuming a valence (bond order) model for the description of the S-I-I system within C.-T. adducts, with n(I-I) + n(E-I) = 1... 

Valence bond theory does agree fairly well with molecular orbital (MO) theory for homonuclear diatomic molecules that can obey the octet rule H2 (single bond, bond order = 1), Li2 (single bond, bond order = 1), N2 (triple bond, bond order = 3), 02 (double bond, bond order = 2), F2 (single bond, bond order = 1). However, for those molecules that don t, it is more difficult to know if they exist or not and what bond orders they have. MO theory allows us to predict that He2, Be2 and Ne2 do not exist since they have bond orders = 0, and that B2 has bond order = 1 and C2 has bond order = 2. 

SB The H2 ion contains 1 electron from each H plus 1 electron (for the charge) for a total of three electrons. Its molecular orbital diagram is ol3l] au [T]. There are 2 bonding and 1 anti-bonding electrons. The bond order in H2 is ... 

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