Ring strain Quotes

“Wikipedia: Ring strain”

“Cyclopropane is the most strained of all rings, primarily because of the angle strain caused by its 60°C C-C bond angles. In addition, cyclopropane has considerable torsional strain because the C-H bonds on neighboring carbon atoms are eclipsed … Cyclobutane has less angle strain than cyclopropane but has more torsional strain because of its larger number of ring hydrogens. … Cyclopentane was predicted by Baeyer to be nearly strain-free, but it actually has a total strain energy of 26 kJ/mol (6.2 kcal/mol). Although planar cyclopentane has practically no angle strain, it has a large amount of torsional strain. Cyclopentane therefore twists to adopt a puckered, nonplanar conformation that strikes a balance between increased angle strain and decreased torsional strain.”

“To measure the amount of strain in a compound, we have to measure the total energy of the compound and then subtract the energy of a strain-free reference compound. The difference between the two values should represent the amount of extra energy in the molecule due to strain. The simplest experimental way to do this for a cycloalkane is to measure its heat of combustion, the amount of heat released when the compound burns completely with oxygen. … Thus, three kinds of strain contribute to the overall energy of a cycloalkane. … Angle strain—the strain due to expansion or compression of bond angles … Torsional strain—the strain due to eclipsing of bonds on neighboring atoms … Steric strain—the strain due to repulsive interactions when atoms approach each other too closely.”