Relative bond strengths

Relative bond strengths of some of the more conunon bonds in organic molecules are shown in Table 2.6. Bond strength ranges from the weakest in the upper left to strongest in the lower right of the table. 

11 Mass spectra of (a) n-butyl chloride, (b) n-butyl bromide, and (c) n-butyl 

Such straightforward correlations between bond strengths and fragmentation patterns are seldom observed, but it will be useful to glance at this table as we discuss various types of fragmentations and various classes of compounds. 

Compare the isotope peak intensities with those in Table 2.4. 

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However, the situation is not as clear-cut as it might at first seem since a variety of other factors may also contribute to the above-mentioned trend. Abuin et a/.141 pointed out that the transition state for addition is sterically more demanding than that for hydrogen-atom abstraction. Within a given series (alkyl or alkoxy), the more nucleophilic radicals are generally the more bulky (i.e. steric factors favor the same trends). It can also be seen from Tabic 1.6 that, for alkyl radicals, the values of D decrease in the series primary>secondary>tertiary (i.e. relative bond strengths favor the same trend). 

J 8 Predict and explain relative bond strengths and lengths (Sections 2.14—2.16). 

Figure 8.25. Predicted volcano plots for ammonia synthesis, showing the turnover frequency versus the relative bonding strength of N atoms to the surface for ammonia concentrations of 5%, 20%, and 90%. The left-hand panel corresponds to conditions of...

The derivation of thermochemical information from radiative association seems to have promise for precise and rapid relative bond strength comparisons among related complexes. Comparisons among different metal ions binding to the same... 

Problem 6.4 Predict (a) the geometry of ethylene, H,C=CH, (f>) the relative C-to-C bond lengths in ethylene and ethane (c) the relative C—H bond lengths and bond strengths in ethylene and ethane (d) the relative bond strengths of C—C and C==C. ... 

Predict the structures and bonding in donor-acceptor complexes of ammonia with F2, , and C1F. What are the expected relative bond strengths Are your predictions in accord with the results of high-level theoretical calculations of Roggen and Dahl (Roggcn, I. Dahl, T., J. Am. Chem. Soc., 1992, 114, 511) ... 

Relative bond strength of major elements in various oxygen coordinations compiled by Povarennykh (1963)... 

Element in stated oxygen coordination Relative bond strength 0 ) Element in stated oxygen coordination Relative bond strength ( ) Element in stated oxygen coordination Relative bond strength (0)... 

N.B.x In parentheses are oxygen atomic coordinations where the relative bond strength is higher than one in low valence atoms, usually occurring in group form. 

A detailed study of these switching reactions has been made by Adams et al.76 who determined the relative bond strengths of a series of molecules to both 02 and 02 and recognised that the 0 J NO ion formed in reaction (59) is not the stable nitrate ion, NOJ, but the more reactive peroxy isomer which reacts with NO ... 

Recent thermochemical determinations suggest that A = 14.21 kcal/mol and B 17.21 kcal/mol (llg). To obtain, for instance, benzylic C-X bond strengths, the stabilization energy calculated from equation 9 is subtracted from C-X bond strengths for corresponding saturated species. Recent studies of alkyl-benzene pyrolysis (117) imply that within current uncertainties in relative bond strengths this formula applies to secondary and... 

The numerical values for these quantities have been extracted and summarized in Table V. These results did not surprise us, since they were predicted by ionic model calculations (19) as well as one ab initio Hartree-Fock calculation for lithium fluoride (20) (a subsequent one is also shown in Table V) which treated both monomer and dimer. However, the trend is opposite to that observed with metal and noble gas dimers, whose I.P. s are lower than the corresponding monomers. It is simply a consequence of the relative bonding strengths of the two units in the neutral and ionic forms. Alakll halide dimers are more stable as neutrals metal and noble gas dimers are generally more stable as ions. 

By way of assessment of the relative bond strengths, the following correlations have been drawn up (see also Table 1). 

The free energy change (AG ) depends on the enthalpy change (Aff°) and the entropy change (A5°). AH° indicates relative bond strength, but what does AS° measure ... 

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