* This theory proposed by Baeyer to explain the relative stability of cycloalkanes.
* According to this theory the open chain alkanes contain sp3 hybridized carbon atoms, thus the bond angle is 109o28'.
* The bond angle ( 109o28' ) is resposible for the stability of alkanes hence forth it is called Ideal Bond angle.
* The distortion ( deviation ) in Ideal Bond angle leads into unstability of that hydrocarbon.
* The cycloalkanes contain sp3- hybridized carbon atoms but they do not have Ideal Bond angle exactly 109o28' due to formation of ring.
* The strain occurs on Ideal Bond angle in cycloalkanes due to formation of ring. This Bond angle strain in the ring is called angle strain.
* It is also reported that more the angle strain lesser is stability of cycloalkane or less the angle strain more is the stability of cycloalkane.
* The angle strain is calculated by the formation given below.
Angle strain = Ideal Bond angle - Actual Bond angle
* Let us see the angle strain of some cycloalkanes.
Name of cycloalkanes Ideal Bond angle Actual Bond angle Angle strain
1) Cyclopropane 109o 60o 49o
2) Cyclobutane 109o 90o 19o
3) Cyclopentane 109o 108o 1o
4) Cyclohexane 109o 120o -11o=11o
* On the basis of above angle strains the order of stability of cycloalkanes is a below.
Cyclopentane > Cyclohexane > Cyclobutane > Cyclopropane