Cyclobutane ring strain

Cyclobutane has the second largest heat of combustion per CH2 group (686.0 kJ mol-1) => cyclobutane has the second largest ring strain (109 kJ mol-1). 

The Origin of Ring Strain in Cyclopropane and Cyclobutane Angle Strain and torsional Strain... 

It is noteworthy to point out that the rate of retro-aldol reaction is enhanced by ring strain. Thus, suitably substituted 3-oxygenated carbonyl cyclobutanes would... 

Another skeletal rearrangement involving the strained cyclobutane ring was recently reported 93). The formic acid catalyzed reaction converted the compound (273)... 

We know that all cycloalkanes do not have the same relative stability. Cyclohexane is most stable while cyclopropane and cyclobutane are much less stable, because they have a ring strain in their molecules. 

As an illustration, the ring strain in cyclopropane, cyclobutane and cyclohexane and cyclodecane has been calculated ... 

Cyclic allenes have improved reactivity due to ring strain. The cycloaddition of 1,2,4-cyclohexatriene (28) with styrene (29), for example, afforded exclusively cyclobutane 31 (equation 9)18. Semi-empirical calculations (AMI) determined the diradical intermediate 30 to be at an energy minimum19. 

Stability. The four-membered ring in the diazabiphenylene series of compounds is strained due to bond angle deformation . The conventional ring strain energy for cyclobutane is 111 kj moP alkyl substituents stabilize the ring by only a few kilojoules per mole. 

Problem 9.9 Explain why the ring strain of cyclobutane is only slightly less than that of cyclopropane. ... 

One of the problems associated with thermal cyclodimerization of alkenes is the elevated temperatures required which often cause the strained cyclobutane derivatives formed to undergo ring opening, resulting in the formation of secondary thermolysis products. This deficiency can be overcome by the use of catalysts (metals Lewis or Bronsted acids) which convert less reactive alkenes to reactive intermediates (metalated alkenes, cations, radical cations) which undergo cycloaddilion more efficiently. Nevertheless, a number of these catalysts can also cause the decomposition of the cyclobutanes formed in the initial reaction. Such catalyzed alkene cycloadditions are limited specifically to allyl cations, strained alkenes such as methylenccyclo-propane and donor-acceptor-substituted alkenes. The milder reaction conditions of the catalyzed process permit the extension of the scope of [2 + 2] cycloadditions to include alkene combinations which would not otherwise react. 

Due to the ring strain in the cyclobutane ring, /(-carbonyl cyclobutanones made by oxidation of methylenecyclobutane in methanol will readily undergo retro-Claisen-type reactions. For ozonolysis, this can be avoided by changing the solvent from methanol to dichloromethane treatment of 6-methyl-8-methylene-m-3-oxabicyclo[4.2.0]octan-2-one with ozone in methanol gave methyl 2-(4-methyl-2-oxo-4-tetrahydropyranyl)acetate (1), while the same treatment in dichloromethane gave 6-methyl-m-3-oxabicyclo[4.2.0]octane-2,8-dione (2).16... 

Pinacol rearrangement driven by the release of the ring strain of a cyclobutane ring has been employed in an extremely efficient manner to form cyclopentanone derivatives. Experimentally. the Lewis acid mediated aldol condensation of benzaldehyde with l,2-bis(trimethyl-siloxy)cyclobutcne at —78 C gave the pinacol 1 in its silylated form.35,36 Subsequent treatment of this pinacol with trifluoroacetic acid at room temperature afforded 2-phenyl-cyclopentane-l,3-dione (2) in 97% yield.35,36... 

C-C bond Fluonnation increases the bond strengths in cycloalkanes, including cyclobutanes [75, 94], but by contrast, it decreases C-C bond strengths and increases ring strain in cyclopropanes and other three-membered nng compounds [75 94, 95]... 

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