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Carbon and its compounds are the essential building blocks of many natural compounds that we see in today’s world. Understanding these compounds, their geometry, and the way they react due to this geometry is the key to understanding many reactions that take place around us. But many of these compounds do not have fixed geometries and alternate between a set of shapes.
This gives rise to a new concept in the geometry of compound molecules called conformations. Carbon compounds are divided into three categories according to the carbon carbon bond that they exhibit. Alkane, alkene, and alkyne are the three types of carbon compounds that are found in nature. One of the most important alkanes is ethane. The content will outline the definition and the two conformations of ethane.
Ethane
Ethane is the second type of compound that is found in the alkane family of carbon compounds. All alkanes share a common property – all the carbon carbon bonds present in any alkane is always a single bond.
Ethane has the formula C2H6 and has a single carbon carbon bond. It is widely used in a lot of industrial as well as small scale activities. From making large amounts of ethylene to the ethanol found in alcoholic beverages, ethane is the most common carbon compound used in today’s world.
The single bond present in ethane is actually a sigma bond. Sigma bonds are special bonds that are formed when covalent bonding takes place. Covalent bonds involve the sharing of electrons that are present in the outermost shells of the atom. Carbon has four atoms in its valence shell and actively uses them to form covalent bonds.
Sigma bonds are the strongest covalent bonds found in nature. They owe their strength to the direct overlapping of atomic orbitals. This creates a common electron region that is strongly attached to both the molecules or atoms that are involved in creating a covalent bond. Since ethane has a single sigma bond, and no other types of bonds are involved in the covalent bonding, this gives rise to two important conformations of ethane.
Conformers
Conformers are special structures that are formed due to the changes in geometrical shapes that happen when molecules rotate around the axis of the bonds formed. Any compound can be expressed in three dimensions by describing their bond lengths and the angles between these bonds.
Compounds form conformers to achieve a low energy state. Every molecule and atom wants to achieve a stable state which means it wants to have a low energy state. When the functional groups in a carbon compound are significant in size and a specific spatial orientation of these groups gives a defined amount of energy to the compound, then these compounds undergo spatial changes to form conformers.
Conformers are visualised by using a set of specific notations for the bonds and the molecules. One of the most widely used methods is Newman’s projection method. In this method, wedges and dashes are used to represent bonds. Since the paper we draw on is two dimensional in nature, a wedge denotes that the bond is coming out of the plane of the paper towards the person holding it. On the contrary, a dash denotes that the bond is going below the plane of the paper away from the person holding it.
In Newman’s projection, a particular bond in the compound is selected as the bond of interest. Then the structure is drawn such that the atom in the front of the bond is represented by a dot while the atom in the back is drawn as a circle. Bonds are then drawn with respect to the atoms to which they are bonded to.
Conformations of Ethane
Ethane has a single carbon carbon bond around which it rotates. It could also rotate around the carbon hydrogen bonds but that rotation will not yield a spatially different compound. Therefore, the sigma bond between the two carbons is the bond of interest.
Sigma bonds are formed on the basis of overlap between the bonded atoms. Such bonds are cylindrical in nature. Therefore, it can ensure that it has a full degree of overlap even when its two ends are rotated. This means that a low amount of energy is required to rotate around the sigma bonds as they are not disturbed by the rotation of the bonded atoms.
According to Newman’s structure of ethane, the front carbon has three hydrogen atoms bonded to it and the back atom also has three hydrogen atoms bonded to it. The first conformer is formed when the carbon hydrogen bonds in the front atom are at 60 degrees to the carbon hydrogen bonds in the second atom.
This creates a staggered shape conformer of ethane. This state holds the lowest energy and is very stable since the carbon hydrogen bonds in the front are farthest to the carbon hydrogen bonds in the back. The electronic repulsion is at its minimum and reduces the total energy of the molecule.
By rotating the bonds in the front carbon in the staggered conformation by another 60 degrees, the carbon hydrogen bond in the front line up exactly with the carbon hydrogen bonds in the back. This creates an eclipsed conformation in which the torsional strain i.e. the repulsion between the carbon hydrogen bonds in the front and back is at maximum. The state is a high energy state and not stable.
Conclusion
Conformers are special structures that are formed due to the changes in geometrical shapes that occur when molecules rotate around the axis of the bonds that are formed. Any compound can be expressed in three dimensions by describing their bond lengths and the angles between these bonds.
Ethane has a single sigma bond and no other types of bonds involved in the covalent bonding, and this gives rise to two important conformations of ethane. The first conformer is formed when the carbon hydrogen bonds in the front atom are at 60 degrees to the carbon hydrogen bonds in the second atom. This creates a staggered shape conformer of ethane.
By rotating the bonds in the front carbon in the staggered conformation by another 60 degrees, the carbon hydrogen bond in the front lines up exactly with the carbon hydrogen bonds in the back creating an eclipsed conformation.
