Strain Energy of the Cyclopropane Ring

The strain energy of the cyclopropane ring is determined from thermochemical measurements on two closely related compounds the /r-butyl ester of cyclopropanecarboxylic acid and the methyl ester of cyclohexanecarboxylic acid. Both compounds can be synthesized from the appropriate acid chlorides, and their heats of combustion measured with a bomb calorimeter. 

The molar enthalpy change A//a for dissociation of an organic compound into separated atoms in their gaseous state 

For all conventional chemical bonds, the 5, values are positive must have a positive sign for a stable molecule. 

The quantities S and R are defined so as to be positive in sign. We shall be concerned here with the strain energy of the cyclopropane ring, in which the C—C—C bond angles are constrained by geometry to be 60° rather than their normal values, which are in the neighborhood of the tetrahedral angle 109.5°. 

Consider the compounds n-butylcyclopropanecarboxylate (1) and methylcyclohexane-carboxylate (11), which have the same molecular composition C8H14O2  

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The cyclopropenyl cation is the simplest aromatic system, and thus of some theoretical interest. In addition, the chemistry of cyclopropane derivatives is full of Interesting rearrangements to other novel structures,9 reflecting the great strain energy Of the cyclopropene ring. 

Report the yields, boiling ranges, and refractive indexes of the two esters. If available, the VPC and IR curves should be attached to the report. The identification number of the calorimeter and bomb, the individual and average values of the calorimeter heat capacity C(S) and the heats of combustion i Hc for the two esters, and the apparent strain energy for the cyclopropane ring should be reported. An estimate of the uncertainties in C(S), the two A//c values, and S should be given. 

It was demonstrated in Section 3 that spiroannulation of cyclopropane to four- and higher-membered rings does not cause an increase in the strain energy of the molecule. It is not surprising, then, that the chemistry of these compounds does not differ from that of simple alkyl substituted cyclopropanes. Since exciting reviews on the chemistry of cyclopropanes are available42, the authors of this chapter will limit the description of properties of SPC of these types to some of their interesting applications. 

What are the ring strain energies of the simple hydrocarbon rings, cyclopropane... 

The latter occurs despite the fact that the central bond is orthogonal to the SOMO. The reason for this exceptional behavior has been attributed to a much greater strain relief in this process compared to that in which an outer cyclopropane bond is cleaved. Using the ring strain energies of the hydrocarbons as an approximation for those of the... 

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