Multiple bonding operations

Apart from the hardness and softness, two reactivity-related features need to be pointed out. First, iron salts (like most transition metal salts) can operate as bifunctional Lewis acids activating either (or both) carbon-carbon multiple bonds via 71-binding or (and) heteroatoms via a-complexes. However, a lower oxidation state of the catalyst increases the relative strength of coordination to the carbon-carbon multiple bonds (Scheme 1). 

The method of moments of coupled-cluster equations (MMCC) is extended to potential energy surfaces involving multiple bond breaking by developing the quasi-variational (QV) and quadratic (Q) variants of the MMCC theory. The QVMMCC and QMMCC methods are related to the extended CC (ECC) theory, in which products involving cluster operators and their deexcitation counterparts mimic the effects of higher-order clusters. The test calculations for N2 show that the QMMCC and ECC methods can provide spectacular improvements in the description of multiple bond breaking by the standard CC approaches. 

When a reaction involves multiple bonding changes, a question may arise whether the bonding changes occur by a stepwise or concerted pathway. An answer to such a question based on the classical reaction theory is that the reaction proceeds by a concerted pathway, by a stepwise pathway, or by a mixture of the two separate pathways. However, if one takes into account dynamic effects, the answer to the question of concerted versus stepwise may be much more complex. It is interesting to point out here that the case reported by Singleton for the ene reaction affords a case, where stepwise mechanism can dynamically operate on a concerted PES. This contrasts with the reactions described in section Nonstatistical Product Distribution , in which the... 

Where H is the similarity-transformed Hamiltonian, eq (14), with respect to two independent cluster operators T and Z or, more precisely, with respect to the excitation operator T and the deexcitation operator Z The advantage of eq (36) over the expectation value of the Hamiltonian with the CC wave function, which can also improve the results for multiple bond breaking (28, 127), is the fact that EcC(z,j is a finite series in T and Z. Unfortunately, the power series expansions of (Z,7), eq (36), in terms of T and Z contain higher powers of... 

The inductive effect operates along the single bond, or o, system, and results in partial charge separation. In contrast, the mesomeric effect operates along the multiple bond, or n, system, and results in whole units of charge separation. 

Rule (4) accounts for the fact that angles in which multiple bonds are involved are generally larger than those involving only single bonds. A few representative examples are shown in Table 4-6. It should be noted that when the double bond is to an atom less electronegative than those to which the single bonds are directed, the operation of rule (3) reinforces the effect of rule (4). 

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