Ring strain correction

D is correct. Cycloheptane has the most ring strain and is at the greatest energy level. It will produce more heat per mole than methane or ethane because it is a larger molecule. 

The chlorocyclopropane molecule contains three groups and a ring correction. The two methylene groups are identical C-(H)2(C)2. The third structural group, which includes the chlorine, is C-(C)2(H)(C1). The correction for ring strain would be close to that for cyclopropane. 

From the known heat of formation, the bond separation energy of oxirane can be obtained. This is — 14.0 kcal/mol after zero-point correction and is partly a measure of the ring strain. By this criterion, there is a steady reduction in strain energy from cyclopropane to aziridine to oxirane. This trend is reproduced by the theory at the 6-31G level (Table 5). However, even with 7-functions included, the theoretical value for oxirane is still about 5 kcal/mol too negative. 

It seems that the Moller - Plesset corrections for the effects of electron correlation are able to account for the through space influences of the CH repulsions and therby increase the height of the barrier to puckering. Increases in the number of basis functions are able to account for the changes in hybridization that result from the creation of the four membered ring and thus influence the ring strain energy. 

The results are typical of the methods Extended Hiickel overestimates ring strain and favors unbound structures i ). The semiempirical NDO methods usually underestimate ring strain and thus make small rings too stable i >. The ab initio results, which should be the best, are intermediate between the semiempirical ones. The ah initio geometries were not optimized, however, and therefore the absolute energies will not be correct. 

Correction values for ring strain and entropy loss in cyclic hydrocarbon transition [56]... 

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