Comparison rates

Gross rate comparisons indicate that these ring closures proceed considerably faster than analogous substitution reactions not leading to three-membered rings (64AG(E)333). 

Part B of Table 12.2 gives some addition reaction rates. Comparison of entries 19 and 20 shows that the phenyl radical is much more reactive toward addition than the benzy 1 radical. Comparison of entries 22 and 23 shows that methyl radicals are less reactive than phenyl radicals in additions to an aromatic ring. Note that additions to aromatic rings are much slower than additions to alkenes. 

See the discussion of the cleavage of 2-chlorophenyl (below) for oximate rate comparisons. 

Co(Y)CP and Co(HY)Cl react with Fe " " at comparable rates. Comparisons are instructive between this redox reaction and other cation-catalysed chloride-abstraction reactions which occur without simultaneous oxidation-reduction. The intimate mechanisms are likely to be... 

Reaction rate - comparison of batch with micro reactor... 

Comicelles of hydroxy-, phenol-, thiophenoxide-, thiol- and imidazole-functionalized surfactants. Rate comparisons... 

Hydroxy and imidazole functionalized micelles. Rate comparisons... 

Anilide + OH- CTABr + NaOH. Rate comparisons Broxton and Duddy, 19 ... 

O CTABr + NaN02. Rate comparisons Broxton, 1981a,c... 

Carbamate + OH-, Hydrolysis and decarboxylation CTABr + OH-. Rate comparison with variation of substrate Broxton, 1984... 

Ph0)2P0.0C6H4N02-(4) + OH-, ro2 CTABr, CTAC1 + NaOH and peroxy-anions. Rate comparisons and quantitative rate analysis Bunton et al., 1984... 

Figure 10. Rate comparison of periodic to steady-state operation for stoichiometric feed of C0/02 to Pt/AUO, catalyst (38,).

A final note of caution regarding rate comparisons by the spin-trapping technique might be that, despite the apparent simplicity of the procedure outlined here, great care has to be taken with sample preparation in order to achieve the expected reproducibility of ca. 5-10%. Nevertheless, an early prediction that spin trapping would have little quantitative value has proved to be without foundation. 

EM for cyclization of succinamic acid assumed equal to that for cyclization of succinic esters (Table A.2 see text). Direct rate comparisons give EM s for substituted succinamic acids at 25°. No corrections for pX,... 

In 20% dioxan-water (Caswell and Schmir, 1980). Reference reaction as in note m ° EM from direct rate comparison with B.2.19, using Milstien and Cohen s data p EM from direct rate comparison with B.2.23, using Milstien and Cohen s data " Measured under the same conditions as B.2.19-25 r Danforth et al., 1976. For reference reaction see note m Hershfield and Schmir, 1973a. For reference reaction see note m Hershfield and Schmir, 1973b. For reference reaction see note m... 

Rate comparisons for liberation of p-nitrophenol from 10-4 M solutions of amino-acid ester salts in the presence of 5.0 x 10 3 M [323] or [324] at 25.0°Ca... 

Figure 7.32 Screw rotation and barrel rotation flow rate comparison for a deep channel screw [5] running a polypropylene glycol fluid...

Alkynes, although not as prevalent as alkenes, have a number of important uses in synthesis. In general, alkynes are somewhat less reactive than alkenes toward many electrophiles. A major reason for this difference in reactivity is the substantially higher energy of the vinyl cation intermediate that is formed by an electrophilic attack on an alkyne. It is estimated that vinyl cations are about lOkcal/mol less stable than an alkyl cation with similar substitution. The observed differences in rate of addition in direct comparisons between alkenes and alkynes depend upon the specific electrophile and the reaction conditions.111 112 Table 4.4 summarizes some illustrative rate comparisons. A more complete discussion of the mechanistic aspects of addition to alkynes can be found in Section 6.5 of Part A. 

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