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The strain energy of cyclopropane and cyclobutane are 27.5 and 26.3 kcal mol −1, respectively. [1] Cyclopentane experiences much less strain, mainly due to torsional strain from eclipsed hydrogens: its preferred conformations interconvert by a process called pseudorotation. [4]: 14 Ring strain can be considerably higher in bicyclic systems.
a torsion angle between 90° and 150° or −90° and −150° is called anticlinal (ac) a torsion angle between ±150° and 180° is called antiperiplanar (ap), also called anti-or trans-conformation; Torsional strain or "Pitzer strain" refers to resistance to twisting about a bond.
Van der Waals strain is strain resulting from Van der Waals repulsion when two substituents in a molecule approach each other with a distance less than the sum of their Van der Waals radii. Van der Waals strain is also called Van der Waals repulsion and is related to steric hindrance . [ 1 ]
Steric hindrance is often exploited to control selectivity, such as slowing unwanted side-reactions. Steric hindrance between adjacent groups can also affect torsional bond angles. Steric hindrance is responsible for the observed shape of rotaxanes and the low rates of racemization of 2,2'-disubstituted biphenyl and binaphthyl derivatives.
A dihedral angle can indicate staggered and eclipsed orientation, but is specifically used to determine the angle between two specific atoms on opposing carbons. Different conformations have unequal energies, creating an energy barrier to bond rotation which is known as torsional strain. In particular, eclipsed conformations tend to have raised ...
Ring strain theory was first developed by German chemist Adolf von Bayer in 1890. Previously, the only bonds believed to exist were torsional and steric; however, Bayer's theory became based on the interactions between the two strains. Bayer's theory was based on the assumption that ringed compounds were flat.
The interaction between the two flagpole hydrogens, in particular, generates steric strain. Torsional strain also exists between the C2–C3 and C5–C6 bonds (carbon number 1 is one of the two on a mirror plane), which are eclipsed — that is, these two bonds are parallel one to the other across a mirror plane. Because of this strain, the ...
These types of steric interactions are commonly known as 1,3 diaxial interactions. [2] These types of interactions are not present with substituents at the equatorial position. There are generally considered three principle contributions to the conformational free energy: [3] Baeyer strain, defined as the strain arising from deformation of bond ...