Baeyer Strain Theory
Semester-3 Unit-2 Fundamentals of Organic Chemistry
Baeyer Strain Theory
Adolf von Baeyer (a Nobel prize winner) proposed a
theory in 1885 to explain the relative stability of the first few cycloalkane.
1.
Cyclo-alkanes are saturated compounds. So, all the carbons should have normal
tetrahedral angle of 109 o281 (or 109o 51).
2. Any deviation of bond angles from the normal tetrahedral value would, impose a condition of internal strain on the ring called bond angle strain or Beayer strain
3.
Higher value of angle strain of cycloalkane shows instability. As instability
increases reactivity also increase.
4. If all the rings in cycloalkanes assumed to be planar, the bond angle strain for each ring can be calculated below .
yclopentane is more stable due to low angle strain value.
Stability α 1/Angle strain
7. Bayer concludes that rings smaller or larger than cyclopentane are unstable.
According
to Baeyer, the relative order of stability to some common cycloalkanes is as
under:
Cyclopentane
> Cyclohexane > Cyclobutane > Cyclopropane
Actual observed order of stability for
these cycloalkanes is
Cyclohexane > Cyclopentane > Cyclobutane > Cyclopropane
LIMITATIONS OF BAEYER’S STRAIN THEORY
· ✔ Baeyer was not able to explain the
effect of angle strain in larger ring systems
· ✔ According to Baeyer Cyclopentane should be much stable than cyclohexane but practically it is reversed.
· ✔ Larger ring systems are not possible according to Baeyer as they have negative strain but they exist and much stable.
· ✔ Larger ring systems are not planar but wrinkled (puckered) to eliminate angle strain.
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