Conformational Isomers

Introduction

Conformational isomers, also called conformers, are a form or type of stereoisomerism (a type of isomerism where molecules have the same molecular formula but different 3-D orientations of atoms in space ) in which the isomers can easily be interconverted only by rotating them about their single bond or sigma bond.

And these conversions can take place at room temperature. This is because the energy required to change or convert one form of conformational isomer to another is usually or generally deficient, so the conversion can easily occur at room temperature. Some examples of conformational isomers are ethane, n-butane, etc.

What is Conformation?

Conformation is defined as anyone or unique of the infinite or multiple numbers of all possible spatial or 3-D arrangements of atoms in the molecule that occurs due to the rotation or twisting of their constituent groups of atoms about sigma or single bonds. Different types of Conformations or conformers are easily possible for any molecule that holds a single covalent bond that connects or joins two polyatomic groups, and in each of them, there exists at least one or minimum one atom that does not lie along or by the axis of that single bond in the molecule.

• And one simplest example of such a molecule is Hydrogen peroxide; here, the two hydroxyl groups can easily rotate or twist with respect to each other about or through the axis of the oxygen-oxygen bond. And every distinct Conformation of the same molecule highlights or represents a state which holds different potential energy.

Vladsinger, Isomerism, CC BY-SA 3.0

Conformational Isomers

Conformational isomers are also called rotational isomers or conformers. These are types of stereoisomers(isomers having the same molecular or empirical formula but differ in the spatial or 3-D arrangement of their atoms) produced due to rotation or twisting of sigma bonds or single bonds about their axis. In conformational isomerism, isomers can easily be interconverted just by rotating them about sigma or a single bond. And these conversions are possible at room temperature because the energy required for converting from one form to another is very low. Some conformational isomers or arrangements are assigned some specific notation based on the dihedral angles formed between the vicinal groups. Such examples are staggered, skewed, and eclipsed for ethane, and for n-butane, it is anti or gauche Conformation.

Different forms of ethane are based on their dihedral angles.

Representation of Eclipsed and Staggered Conformation

• Eclipsed Conformation − This type of Conformation formed due to the formation of a 0° dihedral angle between the arrangement of atoms or the group of atoms in a molecule. Due to this type of arrangement of atoms the stability of this Conformation is very low. Here, the bond electron pairs experience high repulsion because there are no spaces available between the atoms or groups of atoms. Due to less stability, the molecule possesses higher potential energy.

Dissolution, Staggered and eclipsed, CC BY-SA 3.0

• Staggered Conformation − This type of Conformation formed due to the formation of a 60° dihedral angle between the arrangement of atoms or the group of atoms in a molecule. Due to this type of arrangement of atoms the strain of this Conformation is very low

• Here, the bond electron pairs experience very low repulsion because there are spaces available between the atoms or groups of atoms. So, this is the most stable Conformation. Due to high stability molecules possess lower potential energy.

Dissolution, Staggered and eclipsed, CC BY-SA 3.0

Sawhorse projections

Sawhorse projection is the projection of a molecule from an angle rather than or instead of side-on projection. This projection resembles Newman's projection but the difference is that this projection shows the carbon-carbon(C-C) bond in the middle of the molecule. And, we can also draw this type of projection in both the eclipsed or staggered Conformation. In this type of projection, there is no need to show hydrogen atoms all the time.

Newman projections

Newman projection is the basic visualization of a chemical bond that appears from the front to back, the atom present at the front is denoted by a dot, whereas a circle denotes the atom at the back. This projection plays a very important role in the stereochemistry of alkanes. In this projection, the carbon atom present at the front is called “proximal carbon” and the carbon present at the back is called “distal carbon”. This Newman projection is also very useful for determining the dihedral angle of the front(proximal) and back(distal) carbon atoms.

I, Amelliug, Newman, CC BY-SA 3.0

Conclusion

Conformational isomers also called conformers or rotational isomers are the isomers with the same molecular formula but the different spatial arrangements of atoms or a group of atoms that are interconverted from one form to another by rotating around sigma or a single bond at room temperature. Eclipsed Conformers are formed due to the formation of a 0° dihedral angle between the arrangement of atoms or the group of atoms in a molecule and, staggered Conformers are formed due to the formation of a 60° dihedral angle between the arrangement of atoms or the group of atoms in a molecule. Sawhorse projection is the angular projection of the molecule whereas Newman projection is the side-on projection of the molecule.

FAQs

1. What are conformers?

Conformers also called conformational isomers are the different forms of isomers of the same molecule produced due to the rotation of a sigma bond or a single bond in the molecule.

2. Why is the interconversion of the conformational isomers possible at room temperature?

In conformational isomers interconversion from one form to another is possible at room temperature because the energy required for the conversion is deficient.

3. What do you mean by dihedral angle?

The dihedral angle is the angle formed due to the intersection of two planes with each other. And, the two intersecting planes are cartesian.

4. What are the dihedral angles present in the eclipsed and staggered form respectively?

In the eclipsed form, the dihedral angle form is 0°; for the staggered form, the dihedral angle form is 60°.

5. What is the basic difference between the sawhorse projection and the Newman projection?

Sawhorse projection is the projection of a molecule from an angle whereas Newman projection is a side-on projection(deflected images) of the molecules.