"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."