Skeletal bond length

An even stronger case of intramolecular RAHB coupling is provided by the maleate ion (HOOCCH=CHCOO-), whose H-bonded and open conformers are shown in Fig. 5.22. Skeletal bond lengths and bond orders of these conformers are compared in Table 5.18. As shown in Fig. 5.22, the H-bonded conformer is favored in this case by more than 26 kcalmol-1, which is indicative of a powerful intramolecular no aoH interaction (estimated second-order stabilization 104 kcalmol-1) that is sufficient to overcome the severe steric repulsion of the extremely short H- -O nonbonded distance ( 1.3 A).56... 

In parentheses are the HF/3-21G values calculated on the AMI optimized structures. Average skeletal bond lengths. 

Table 7 reveals that the skeletal bond lengths tend to shorten with an increase in the negative charges on the skeletal atoms due to silyl substituents, regardless of their steric bulk. This is also confirmed by the geometry optimization at the HF/3-21G level of... 

Fig. 1.28. Comparisons among the rotational isomeric (RIS) radial distribution functions at 413 K for polyethylene (o) and PDMS ( ) chains having n — 20 skeletal bonds, and the Gaussian approximation ( — ) to the distribution for PDMS [45]. The RIS curves represent cubic-spline fits to the discrete Monte Carlo data, for 80 000 chains, and each curve is normalized with respect to an area of unity (with / being the skeletal bond length).

As has been shown above, a polymeric chain can be simulated with the aid of Equation 2.10. This equation allows both crosslinked polymer topology (the values and are functions of the chemical crosslinking density v ) and its molecular characteristics (the value is defined by skeletal bond length f and characteristic ratio C, which serves as an indicator of the chain statistical flexibility and also depends on Z ) to be accounted for [131]. 

ISC (I/O-11.3) searches employed restricted MAXSTEP parameters (and increased MAXCYCLE parameters) to preserve fragile CAS convergence from step to step of geometry optimization.] As seen in EO-11.3, the twisted ISC(So/Ti) geometry resembles that of the CI(So/Si) species (FO-11.2) with altered skeletal bond lengths and slightly inverted pyramidahzation at C(2). 

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