Torsional Strain and Steric Strain
TLDRThis chemistry lesson distinguishes between steric and torsional strain, focusing on molecular stability and conformations. Torsional strain, associated with the twisting of bonds, particularly in ethane's eclipsed conformation, arises from electron repulsion in CH bonds. Steric strain, on the other hand, results from the repulsion of electron clouds when bulky groups are close, evident in both eclipsed and staggered conformations. The tutorial illustrates these concepts with examples, including the comparison of energy values for different interactions, and emphasizes the importance of recognizing eclipsed conformations for torsional strain and the proximity of bulky groups for steric strain.
Takeaways
- π Torsional strain is the resistance to twisting a bond due to electron repulsion in the CH bonds, particularly in the eclipse conformation of ethane.
- π Torsional strain is associated with the twisting of an object, which is less stable and at a higher potential energy compared to the staggered conformation.
- π The term 'torsion' refers to the action of twisting or the state of being twisted, which is key to understanding torsional strain.
- π£ Torsional strain occurs in bonds that are three bonds apart, as opposed to steric strain which can occur between atoms more than three bonds apart.
- π« Steric strain arises from the repulsion between electron clouds of atoms that are close to each other, especially when bulky groups are involved.
- π Steric strain can be present in both staggered and eclipse conformations if bulky groups are within 60 degrees apart.
- π Torsional strain is specifically found in eclipse conformations, where atoms are directly behind one another, causing electron repulsion.
- π The energy values for different types of strain are provided, with hydrogen-hydrogen eclipse interaction having more energy than two CH3 groups in a gauche interaction due to proximity.
- π Steric strain can occur in both conformations, but torsional strain is exclusive to the eclipse conformation.
- π Newman projections are used to illustrate and compare different conformations, helping to identify torsional and steric strain.
- π To simplify, remember that an eclipse conformation indicates torsional strain, and the presence of bulky groups next to each other indicates steric strain.
Q & A
What is the definition of torsional strain?
-Torsional strain is the resistance to twisting a bond due to the applied torque or rotational force, which is associated with the twisting of an object.
How is torsional strain related to the conformations of ethane?
-Torsional strain in ethane is observed when the molecule transitions from a staggered conformation, where hydrogen atoms are not eclipsed, to an eclipsed conformation, where they are.
What is the difference in stability between staggered and eclipsed conformations of ethane?
-The staggered conformation is more stable and at a lower potential energy due to less electron repulsion, while the eclipsed conformation is less stable and at a higher potential energy because of greater electron repulsion in the CH bonds.
Why does torsional strain occur in the eclipsed conformation of ethane?
-Torsional strain occurs in the eclipsed conformation because of the electron repulsion between the CH bonds when the hydrogen atoms are aligned, causing the molecule to resist this unstable arrangement.
Where is torsional strain typically found in molecular structures?
-Torsional strain is typically found in bonds of atoms that are three bonds apart, where an eclipsed arrangement can occur.
What is steric strain and how does it differ from torsional strain?
-Steric strain arises when atoms or groups that are more than three bonds apart come close to each other, causing electron cloud repulsion. It differs from torsional strain, which is due to electron repulsion in bonds that are three bonds apart and specifically in eclipsed conformations.
Can steric strain occur in both staggered and eclipsed conformations?
-Yes, steric strain can occur in both conformations, especially when bulky groups are within 60 degrees of each other in a staggered conformation or are eclipsed in an eclipsed conformation.
What is the significance of the term 'gauch interaction' in the context of steric strain?
-The term 'gauch interaction' refers to the steric strain that occurs when two bulky groups are 60 degrees apart in a staggered conformation, causing electron cloud repulsion.
How can one identify torsional strain in molecular structures?
-Torsional strain can be identified by looking for the eclipsed conformation, where atoms are aligned and cause electron repulsion in the bonds.
What are the energy values associated with different types of strain in molecular structures?
-The relative potential energy for two hydrogen atoms eclipsed in ethane is 4 kilojoules per mole, for hydrogen and methyl it's 6, for two methyl groups it's 11, and for the steric interaction between two methyl groups, it's 3.8.
Why does the hydrogen-hydrogen eclipse interaction have more energy than two CH3 groups in the gauche interaction?
-The hydrogen-hydrogen eclipse interaction has more energy because the atoms are much closer together, despite being smaller and less bulky than methyl groups, which are farther apart even in the gauche interaction.
Outlines
π Understanding Torsional and Steric Strain
This paragraph explains the concepts of torsional and steric strain in chemistry. Torsional strain is associated with the twisting of bonds due to applied torque, exemplified by the staggered and eclipsed conformations of ethane. The staggered conformation is more stable due to less electron repulsion in the CH bonds compared to the eclipsed conformation, which has higher potential energy. Steric strain, on the other hand, results from the repulsion between electron clouds of atoms that are close to each other, typically occurring when bulky groups are in proximity. The paragraph distinguishes torsional strain as being present in eclipsed conformations and steric strain being possible in both staggered and eclipsed conformations if bulky groups are involved.
π Comparing Torsional and Steric Strain in Organic Chemistry
The second paragraph delves deeper into the differences between torsional and steric strain, using Newman projections of 2,2-dimethylbutane as examples. It clarifies that torsional strain is identified with eclipsed conformations where atoms are directly behind one another, leading to electron repulsion. Steric strain is present when bulky groups, such as methyl groups, are close enough to repel each other, which can occur in both staggered and eclipsed conformations if the groups are within 60 degrees of each other. The paragraph also discusses the relative potential energy values associated with different types of strain, noting the higher energy of hydrogen-hydrogen eclipsed interactions compared to methyl groups in gauche interactions due to the closer proximity of the smaller atoms.
π Recap of Steric and Torsional Strain Concepts
The final paragraph provides a summary of the key points regarding steric and torsional strain. It reiterates that torsional strain is specific to eclipsed interactions, while steric strain can occur in both eclipsed and staggered conformations when bulky groups are in close proximity. The paragraph emphasizes the importance of recognizing these strains in organic chemistry, particularly noting that the presence of an eclipsed conformation typically indicates torsional strain, and the adjacency of bulky groups suggests steric strain.
Mindmap
Keywords
π‘Torsional Strain
π‘Staggered Conformation
π‘Eclipsed Conformation
π‘Sterichind Strain
π‘Electron Repulsion
π‘Potential Energy
π‘Methyl Group
π‘Newman Projection
π‘Gauch Interaction
π‘Kilojoules per Mole
Highlights
The lesson discusses the difference between steric strain and torsional strain.
Torsional strain is related to the twisting of an object due to applied torque or rotational force.
Torsional strain is the resistance to twisting a bond, exemplified by the staggered and eclipsed conformations of ethane.
Ethane's staggered conformation is more stable with lower potential energy due to less electron repulsion.
Eclipse conformation in ethane has higher potential energy and is less stable due to electron repulsion in CH bonds.
Torsional strain arises from the repulsion of electrons in CH bonds when atoms are eclipsed.
Torsional strain is found in bonds of atoms that are three bonds apart.
Steric strain occurs when bulky groups are close, causing electron cloud repulsion.
Steric strain can be present in both staggered and eclipsed conformations if bulky groups are within 60 degrees apart.
Torsional strain is specific to eclipse conformations, whereas steric strain can occur in both conformations under certain conditions.
Newman projection is used to compare eclipsed and staggered conformations in two methyl butane.
Eclipsed conformations with hydrogen or methyl groups exhibit torsional strain due to electron repulsion.
Steric strain in staggered conformation occurs when bulky groups like methyl groups are within 60 degrees of each other.
The energy values for different types of strain are provided, with hydrogen-hydrogen eclipse interaction having the highest at 4 kJ/mol.
The reason for higher energy in hydrogen-hydrogen eclipse interaction compared to methyl groups in gauche interaction is due to closer proximity.
Methyl groups in staggered interaction have less potential energy than hydrogen atoms in eclipse interaction due to increased distance.
A mnemonic for organic chemistry exams: eclipse conformations indicate torsional strain, and bulky groups next to each other indicate steric strain.
Transcripts
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