Key Difference – Staggered vs Eclipsed Conformation
The two terms, Staggered and eclipsed conformation(two main branches of the Newmann projections) are used in Organic Chemistry to explain the arrangement of atoms in some organic molecules. In terms of stability, staggered conformation is more stable than eclipsed formation. The formation of the staggered confirmation is more favourable since its conformational energy is minimum. This is the key difference between staggered and eclipsed conformation.
What is Staggered Conformation?
Staggered conformation is a chemical conformation of an ethane-like molecule (CH3-CH3=abcX–Ydef) in which the substituents a, b, and c are attached at the maximum distance from d, e, and f. In this case, the torsion angle is 60° and the conformational energy is minimum. The main requirement for this confirmation is an open chain single chemical bond to connect two sp3hybridisedatoms. Some molecules such as n-butane can have special versions of staggered confirmations: gauche and anti.
What is Eclipsed Conformation?
Eclipsed conformation can exist in any open chain when a single bond connects two sp3hybridized atoms. In this case, the two substituents (let’s say -X and -Y) on adjacent atoms (say A and B) are in the closest proximity. In other words, the torsion angle X–A–B–Y is 0° in the molecule. This confirmation possesses the maximum conformational energy because of steric hindrance.
What is the difference between Staggered and Eclipsed Conformation?
Structure:
Staggered Confirmation: Staggered confirmation can be best understood by using an ethane molecule. When we take a look from the side, its staggered confirmation can be illustrated as follows.
Eclipsed Conformation: Ethane molecule can be taken as one of the simplest examples to understand the eclipsed conformation.When we take a look from the side, the eclipsed conformation of ethane molecule can be seen as follows.
Stability:
Staggered Confirmation: Staggered confirmation can be considered as the most favourable conformation since it has reduced the strain in the molecule. Because the attachments in the molecule are more evenly spaced out and this reduces the repulsion between the front carbon’s attachments and the back carbon attachments. In addition, the staggered conformation is stabilized by the hyperconjugation.
Eclipsed Conformation: The eclipsed conformation is less favorable because it can have more interactions between the front and back substituents; this creates more strain. Angles between the front and back substituents can be anything.
Potential Energy:
The graph of the potential energy variation as a function of the dihedral angle (dihedral angle between two hydrogens on different carbons) shows the energy difference between staggered confirmation and eclipsed confirmation.
Staggered Confirmation:
The above plot shows that the staggered conformation has the minimum potential energy. This implies that this is the most stable form and it can be the most favourable form over the other confirmations.
Eclipsed Conformation:
According to the above graph, eclipsed confirmation has the maximum potential energy. This implies that the eclipsed conformation is a transition state and it can never exist in this form.
Definitions:
Conformations:
Conformations are the different positions a molecule can take while keeping the atoms and bonds on the molecule. In this case, the only variation is the angles in which certain parts of the molecule are bent or twisted.
Torsion angle (dihedral angle):
It referrers to the angle between planes through two sets of three atoms, having two atoms in common. In other words, it is the angle between two intersecting planes.
Reference:
Image Courtesy:
“Newman projection ethane” By Aglarech at de.wikipedia; Leyo – Own work (Public Domain) via Commons Wikimedia