Ring strain influence

In cyclopropane carboxylates the ring strain influences the acidity of the a-carbon, thus the enolates are more difficult to prepare and once made, are more reactive than in the higher-inem-bered rings. These enolates probably do not have an enolate structure, but rather are a-metal-lated species. 

The acidity and hydrogen bond acceptor ability of different phosphine oxides was evaluated by MP2 computational methods. In the case of ring phosphine oxides, the ring strain influenced the properties. ... 

Because of the frequent mutual interference of electronic, inductive, and steric effects, and because of the influence of ring strain, the carbonyl stretching frequency is naturally not an absolute criterion for the methylation course. The heterocyclic systems in question are too diverse for this to hold. Careful inspection of Table I discloses certain deviations from the relationships mentioned. These deviations will now be discussed. 

Ring strain can also exert an important influence on the regioselectivity the hydrogenation of 5-methylenenorbornene over a Ni-boride catalyst (P-2) resulted in preferential... 

The enthalpies of formation of the cycloalkylmagnesium bromides that have been determined by reaction calorimetry are listed in Table 3. As with other functionalized cycloalkanes and the cycloalkanes themselves, there is no regularity to these values with respect to carbon number as there are for their acyclic analogs because of the influence of ring strain on the enthalpies. Unfortunately, there are no enthalpies of formation for the bromocycloalkanes with which to compare these values there are, however, enthalpies of formation for liquid phase cycloalkanes. Figure 3 is a plot of the enthalpies of formation for the cycloalkyl-MgBr vs. those for cycloalkyl-H. There is a linear relationship with... 

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]. 

Progress has also been achieved in developing a comprehensive description of these factors. Anh and Minot s concept, based on Salem s treatment of the Walden inversion, makes it possible to explain experimental trends using a perturbation argument that does not require the introduction of silicon d orbitals. According to this model the major interaction during the reaction occurs between the HOMO of the nucleophile and the LUMO of the substrate. This approach also accounts nicely for the influence of ring strain on the stereochemistry at silicon. 

The P-B bond length determined crystallographically for the (CH2)3-bridged compound 41d (2.092(7) A) is noticeably shorter than that predicted computationally for the related (CH2)2-bridged system 40a (2.21 A). This further substantiates the influence of ring strain on the magnitude of intramolecular P-B interactions. 

How does ring strain in a cycloalkyne influence physical properties and chemical reactivity of these compounds ... 

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