4-3 Stability of Cycloalkanes:Ring Strain Angle strain The strain induced in a molecule when bond angles are forced to deviate from the ideal 109 tetrahedral value(Adolf von Baeyer-1885) o9°(tetrahedral) 49e 108 1209 Cyclopropane Cyclobutane Cyclopentane Cyclohexane
Angle strain ▪ The strain induced in a molecule when bond angles are forced to deviate from the ideal 109º tetrahedral value (Adolf von Baeyer – 1885) 4-3 Stability of Cycloalkanes: Ring Strain
Stability of Cycloalkanes:Ring Strain Angle strain Experimental data show that Baeyer's theory is only partially correct 120 28.7 100 23.9 80 19.1 14.3 9.6 4.8 67891011121314 Ring size Baeyer assumed all cycloalkanes to be flat Angle strain occurs only in small rings that have little flexibility
Angle strain ▪ Experimental data show that Baeyer’s theory is only partially correct ▪ Baeyer assumed all cycloalkanes to be flat ▪ Angle strain occurs only in small rings that have little flexibility Stability of Cycloalkanes: Ring Strain
Stability of Cycloalkanes:Ring Strain The three kinds of strain that contribute to the overall energy of a cycloalkane: 1.Angle strain-the strain due to expansion or compression of bond angles 2. Torsional strain-the strain due to eclipsing of bonds on neighboring atoms 3. Steric strain -the strain due to repulsive interactions when atoms approach each other too closely
The three kinds of strain that contribute to the overall energy of a cycloalkane: 1. Angle strain – the strain due to expansion or compression of bond angles 2. Torsional strain – the strain due to eclipsing of bonds on neighboring atoms 3. Steric strain – the strain due to repulsive interactions when atoms approach each other too closely Stability of Cycloalkanes: Ring Strain