Bond Distances and Strengths

Fundamental Principles of Polymeric Materials, Third Edition. Christopher S. Brazel and Stephen L. Rosen. 2012 John Wiley Sons, Inc. Pubhshed 2012 by John Wiley Sons, Inc. 

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Table 1 Some examples of bond distances and strengths in phosphorus compoimds...

The hydrogen bonds formed between nucleic acid base pairs are crucial to the structure and function of DNA and have therefore been the subject of considerable theoretical work. - Two systems of particular interest are the Watson-Crick guanine-cytosine (GC) and adenine-thymine (AT) base pairs depicted in Figures 5 and 6. Hydrogen bond distances and strengths from high-level ab initio calculations on the GC and AT base pairs could be used to parameterize molecular mechanical force fields that then could be used to study the structure and dynamics of extended double-stranded DNA helices. 

The transfer of a proton in an H-bonded system corresponds to the movement of the proton along its hydrogen bond. This movement is limited by the frequency of approach between the A and B atoms in the H-bonded precursor complex, which is the H-bond vibrational frequency, Vab- It is related to the H-bond distance and strength through the LS potential. For an H-bond strength of 12.5 kJ moU between oxygen atoms, this frequency is Vab = 236 cm The PT is now a first-order reaction and the classical rate constant expressed in terms of this vibrational frequency is... 

Take C—H bond distance and bond strength for example Recalling that an elec tron m a 2s orbital is on average closer to the nucleus and more strongly held than an... 

How do bond distances and bond strengths change with elec... 

The authors pointed out that bond distances and bond strengths, unlike the case for carbon, are of little significance where multiple bonding of the heavier main group metals is concerned. 

Bernhardt and Comba have combined molecular mechanics and the angular overlap model (AOM) to predict the d-d electronic spectra of several hexaamine compounds.The force field used, which had been described earlier, is appropriate for the modeling of Cu(II), Ni(II) (S = 1), Co(III), Fe(III), Cr(III), Zn(II), and Rh(III) complexes of amines, carboxylates, pyridines, and thia ethers. The AOM requires several parameters including metal-ligand cr-and TT-bonding terms [e and e ), interelectronic repulsion terms P- and F" ), and spin-orbit coupling terms Q. The current application uses the empirical relationship e r) = C/r to determine the value of e, where r is the bond distance and C is a constant whose value increases with alkyl substitution. This choice is consistent with the view that N-alkylation increases donor strength. The d-d electronic spectra of a variety of Cr(III), Co(III), and Ni(Il) hexaamine complexes are predicted to within 1000 cm. ... 

PROBLEM 9.3 How do bond distances and bond strengths change with electronegativity in the series NH3, H2O, and HF ... 

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