The Effect of Ring Size

Electron-donating groups in the para position of the perbenzoic acid tend to decrease the rate of reaction . The reverse seems to be true when these groups are present in a 4,4 -disubstituted diaryl sulphoxide. The effect of ring size on the oxidation of cyclic sulphoxides is apparently very small in dioxane-water solution under either acidic or basic conditions . This suggests that no major hybridisation change occurs for the sulphur atom in going to the transition state. 

This review will restrict itself to boron-carbon multiple bonding in carbon-rich systems, as encountered in organic chemistry, and leave the clusters of carboranes rich in boron to the proper purview of the inorganic chemist. Insofar as such three-dimensional clusters are considered at all in these review, interest will focus on the carbon-rich carboranes and the effect of ring size and substituents, both on boron and carbon, in determining the point of equilibrium between the cyclic organoborane and the isomeric carborane cluster. A typical significant example would be the potential interconversion of the l,4-dibora-2,5-cyclohexadiene system (7) and the 2,3,4,5-tetracarbahexaborane(6) system (8) as a function of substituents R (Eq. 2). 

This example illustrates the synthesis of cyclic compounds by intramolecular alkylation reactions. The relative rates of cyclization for ca-haloalkyl malonate esters are 650,000 1 6500 5 for formation of three-, four-, five-, and six-membered rings, respectively.28 (See Section 3.9 of Part A to review the effect of ring size on Sn2 reactions.)... 

Discuss the effect of ring size on the tendency of a cyclic monomer toward ringopening polymerization. 

The mass spectrometry of four-membered heterocycles has been considerably investigated by Scala and Colon. Holmes et have provided structures associated with metastabile ion peaks. The effect of ring size on the fragmentation process of cyclic sulfoxides was studied by Tamagaki and Oae. Thietane 1-oxide appears as a strong radical ion at mje 90. At 80 eV no appreciable deoxygenation takes place. Instead, the loss of OH and/or SOH is observed, giving the peak at mje a value of 73 for CaHjS" and the base peak at mje 41 for CaH ". ... 

Theoretical aspects of the effect of ring size on the acid-catalyzed reduction of cyclic sulfoxides by iodide ions have been studied by Tamagaki et who noticed that differences in reactivity are mainly dependent on the change in activation entropy, which is correlated to the rigidity of the transition complex 220, (Eq. 59). 

Table 5 also gives data on the effect of ring size on the rate which are consistent with observations on other reactions of cyclic compounds. This influence can be explained by the change of the strain in the ring (/ strain) in consequence of the change from sp3 to sp2 hybridisation [129]. 

Actually such sensitized dimerizations have been reported only for small ring, cyclic olefins, the reaction being reasonably efficient for cyclopropenes,262 cyclobutenes,263 and cyclopentenes, but rather inefficient for cyclohexene.264 The effects of ring size on triplet lifetimes... 

It may be of interest to compare the photochemistry of the unsubstituted cyclic ketones. The effect of ring size on the ultraviolet absorption spectrum has been discussed (4,22) although its pertinence to the photochemistry is not obvious. 

S = f. The results demonstrate the effects of ring size and axial ligand on spin state (Table 6). 

Bis-tridentate complexes follow similar trends to those previously discussed, namely, increasing ring size and substitution decreases Dq. A good example of the effect of ring size on the Dq value is in the series m r-[Co(dien)2], /ner-[Co(pet)2] , mcr-[Co(dpt)2], where is 2320, 2240, and 2120 cm , respectively. In the series s- -[Co(dien)2l, s-/oc-[Co(medien)2] , [Co(l,4-me2dien)2] methyl substitution on the amines dramatically decreases the Dq values, 2350, 2250, and 2070 cm" respectively. 

Considering the rather high conformational stability of the series of acetylene-cumulene bisdehydro[4/j-)-2]annulenes, it seems reasonable to assume that the bisdehydroannulenes have approximately the same planarity and essentially the same geometry. Therefore, this series of bisdehydroannulenes makes it possible to study the effect of ring size on the delocalization of a [4 -t-2] tz electron system. The differences in chemical shifts between the signals of the inner protons (tO and the lowest field signal of the outer protons (tq), which are always located at the position nearest to the centre of the molecule, is summarized in Table 9. The chemical... 

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