Newman Projections

The Organic Chemistry Tutor

22 Apr 202123:35

EducationalLearning

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TLDRThis chemistry lesson focuses on drawing Newman projections for various molecules, including ethane, butane, and 2,3-dimethylpentane, to analyze their conformational stability. The instructor explains how to identify staggered and eclipsed conformations, highlighting the anti-conformation as the most stable due to minimal steric strain. The potential energy diagram illustrates the relationship between molecular stability and energy, with the lowest energy conformations being the most stable. The video also covers practice examples to reinforce understanding of conformational analysis.

Takeaways

📚 The lesson focuses on drawing Newman projections for molecules and discussing their relative stability.
🧪 Ethane (CH3CH3) is used as the first example to demonstrate how to draw both staggered and eclipsed conformations.
🔄 The staggered conformation of ethane is more stable due to less torsional strain compared to the eclipsed conformation.
🔍 In the case of butane, the anti-conformation is the most stable, with methyl groups as far apart as possible, minimizing steric strain.
📉 The energy barrier between different conformations is determined by the potential energy diagram, which relates to the stability of the molecule.
🔢 The energy values for different group interactions, such as hydrogen-hydrogen, hydrogen-methyl, and methyl-methyl, are used to calculate the energy barrier.
🌗 The gauche conformation of butane has a dihedral angle of 60 degrees and is less stable than the anti-conformation due to steric strain.
🌑 The eclipsed conformations of butane are less stable, with the total eclipse being the least stable due to maximum steric strain.
📝 When drawing Newman projections, it's important to consider the dihedral angles and the types of group interactions to determine stability.
🔑 The anti-conformation of 2,3-dimethylpentane is the most stable due to the absence of gauche interactions and the separation of bulky groups.
📈 Practice examples, such as 2-methylbutane, illustrate how to determine the most stable conformation by comparing the number and types of steric interactions.

Q & A

What is the main focus of the lesson in the provided transcript?
-The lesson focuses on drawing Newman projections of certain molecules and discussing their relative stability.
What is the first molecule discussed for drawing a Newman projection in the transcript?
-The first molecule discussed is ethane (CH3CH3).
What are the two conformations of ethane mentioned in the transcript?
-The two conformations of ethane mentioned are the staggered conformation and the eclipsed conformation.
Why is the staggered conformation of ethane more stable than the eclipsed conformation?
-The staggered conformation is more stable due to less torsional strain compared to the eclipsed conformation, where hydrogens are eclipsing each other.
What is the specific name given to the most stable Newman projection of butane along the C2-C3 bond?
-The most stable Newman projection of butane along the C2-C3 bond is called the anti-conformation.
What is the dihedral angle between the two methyl groups in the anti-conformation of butane?
-The dihedral angle between the two methyl groups in the anti-conformation of butane is 180 degrees.
What is the term used to describe the conformation where the methyl groups are 60 degrees apart?
-The term used is the gauche conformation.
What is the energy value associated with the eclipse interaction between two methyl groups?
-The energy value associated with the eclipse interaction between two methyl groups is 11 kilojoules per mole.
How many different Newman projections can be drawn for 2,3-dimethylpentane along the C2-C3 bond?
-Several different Newman projections can be drawn for 2,3-dimethylpentane, but the exact number is not specified in the transcript.
What is the energy barrier to rotation for converting butane from its anti-conformation to its totally eclipsed conformation?
-The energy barrier to rotation for converting butane from its anti-conformation to its totally eclipsed conformation is 19 kilojoules per mole.
In the practice example of 2-methylbutane, which conformation is considered the most stable along the C2-C3 bond?
-The most stable conformation of 2-methylbutane along the C2-C3 bond is the one with the lowest potential energy, which has only one gauche interaction.

Outlines

00:00

📚 Introduction to Newman Projections

This lesson focuses on drawing Newman projections of molecules and comparing their stability. Starting with ethane (CH3CH3), the structure is expanded to show C1 attached to three hydrogen atoms. Two conformations, staggered and eclipsed, are illustrated. The staggered conformation is more stable due to lower torsional strain compared to the eclipsed conformation.

05:01

🔬 Newman Projection of Butane

The lesson moves on to butane, drawing its Newman projection along the C2-C3 bond. Carbon 2 has a methyl group and two hydrogen atoms, while Carbon 3 has two hydrogens and a methyl group. The staggered conformation, specifically the anti-conformation, is identified as the most stable due to the maximum separation of methyl groups.

10:03

🧪 Different Conformations of Butane

Additional conformations of butane are explored, including the gauche conformation with a 60-degree dihedral angle between methyl groups, causing steric strain. The stability ranking is provided: anti-conformation (most stable), gauche (second most stable), followed by two types of eclipsed conformations, with the total eclipse being the least stable.

15:12

⚛️ Potential Energy Diagram of Butane

A potential energy diagram for butane is drawn, illustrating how the stability of different conformations relates to their energy levels. The anti-conformation has the lowest energy, while the total eclipse has the highest. The relationship between dihedral angles and potential energy is explained, showing the variations in energy as the molecule rotates.

20:12

🧩 Newman Projection of 2,3-Dimethylpentane

The Newman projection of 2,3-dimethylpentane is drawn along the C2-C3 bond. Carbon 2 has two methyl groups and a hydrogen, while Carbon 3 has a hydrogen, a methyl group, and an ethyl group. Various staggered conformations are considered, with a focus on gauging interactions to determine the most stable configuration.

🔄 Eclipsed Conformations of 2,3-Dimethylpentane

The lesson continues with the eclipsed conformations of 2,3-dimethylpentane. Different configurations are drawn, and their stability is analyzed based on torsional strain. Key interactions, such as between methyl and ethyl groups, are highlighted to compare the potential energy of each eclipsed conformation.

📝 Practice Example: 2-Methylbutane

A practice example involving the most stable conformation of 2-methylbutane along the C2-C3 bond is presented. The structure is analyzed, and different Newman projections are drawn. The focus is on identifying gauche interactions to determine the most stable staggered conformation.

🔍 Energy Barrier in Butane Conformations

The energy barrier between the totally eclipsed conformation and the anti-conformation of butane is calculated. The potential energy of different interactions (CH3-CH3, H-H) is summed to determine the total energy barrier, illustrating the concept of rotational energy barriers in molecular conformations.

Mindmap

Keywords

💡Newman Projection

A Newman Projection is a graphical method used in chemistry to represent the spatial arrangement of atoms in a molecule, particularly around a single bond. It is essential for understanding the three-dimensional structure of molecules like ethane and butane, which are discussed in the video. The script uses Newman Projections to illustrate the staggered and eclipsed conformations of ethane and the various conformations of butane along the C2-C3 bond.

💡Ethane

Ethane is an alkane with the chemical formula C2H6, consisting of two carbon atoms each bonded to three hydrogen atoms. In the video, ethane serves as an introductory example for drawing Newman Projections. The script discusses the staggered and eclipsed conformations of ethane, highlighting the stability differences between these conformations due to torsional strain.

💡Staggered Conformation

A staggered conformation in molecular geometry refers to the arrangement where the atoms or groups attached to the adjacent carbon atoms are as far apart as possible, minimizing steric strain. The video script explains that the staggered conformation of ethane is more stable due to the absence of eclipsing hydrogens, which would cause torsional strain.

💡Eclipse Conformation

An eclipse conformation is a specific type of staggered conformation where certain atoms or groups are aligned directly behind others across a bond. The script describes the eclipsed conformation of ethane as less stable than the staggered conformation because of the torsional strain caused by the overlapping hydrogens.

💡Butane

Butane is another alkane with the formula C4H10, which has a chain of four carbon atoms. The video script discusses the Newman Projections of butane, focusing on the C2-C3 bond, and explains the different conformations such as anti, gauche, and eclipsed, which vary in stability due to steric strain and torsional effects.

💡Anti-Conformation

The anti-conformation is a specific type of staggered conformation where the substituents on each carbon atom are opposite each other, maximizing the distance between them. The video script identifies the anti-conformation of butane as the most stable due to the dihedral angle of 180 degrees between the methyl groups, minimizing steric strain.

💡Gauche Conformation

A gauche conformation occurs when two similar or dissimilar substituents on adjacent carbon atoms are positioned such that the angle between them is approximately 60 or 300 degrees, leading to some steric strain. The script describes the gauche conformation of butane as less stable than the anti-conformation due to the closer proximity of the methyl groups.

💡Dihedral Angle

The dihedral angle is the angle between two planes, commonly used in chemistry to describe the spatial arrangement of atoms in a molecule. In the video, the dihedral angle is used to differentiate between the conformations of butane, with the anti-conformation having a 180-degree angle and the gauche conformation having angles of 60 or 300 degrees.

💡Steric Strain

Steric strain is the energy penalty a molecule experiences when atoms or groups are forced into close proximity, leading to repulsion between electron clouds. The script explains that steric strain affects the stability of molecular conformations, with greater strain leading to higher energy and less stability, as seen in the eclipsed and gauche conformations of butane.

💡Potential Energy Diagram

A potential energy diagram is a graphical representation that shows the potential energy of a molecule as a function of a particular molecular coordinate, such as a dihedral angle. The script uses a potential energy diagram to illustrate the relative stabilities of different conformations of butane, with the anti-conformation at the lowest energy and the eclipsed conformation at the highest.

💡2,3-Dimethylpentane

2,3-Dimethylpentane is a specific alkane with two methyl groups on the second and third carbon atoms of a pentane chain. The video script uses 2,3-dimethylpentane to demonstrate the drawing of Newman Projections and to analyze the stability of different conformations based on the number of gauche interactions and the presence of ethyl and methyl groups.

Highlights

Introduction to drawing Newman projections for molecules and discussing their relative stability.

Ethane (CH3CH3) as the first example for demonstrating the Newman projection along the C1-C2 bond.

Explanation of how to draw a Newman projection for ethane in both staggered and eclipsed conformations.

Staggered conformation of ethane is more stable due to less torsional strain compared to the eclipsed conformation.

Transition to butane and drawing its Newman projection along the C2-C3 bond.

Identification of the anti-conformation of butane as the most stable due to maximum separation of methyl groups.

Description of the gauche conformation of butane with a 60-degree dihedral angle and its associated steric strain.

Eclipsed conformations of butane with varying degrees of stability based on the types of groups eclipsed.

Total eclipse conformation of butane as the least stable due to maximum steric strain.

Potential energy diagram relating the stability of butane conformations to dihedral angles.

Drawing Newman projections for 2,3-dimethylpentane and identifying the most stable conformation.

Analysis of different staggered conformations of 2,3-dimethylpentane based on the number of gauche interactions.

Eclipse conformations of 2,3-dimethylpentane ranked by stability based on torsional strain energy values.

Practice example: Drawing the most stable conformation of 2-methylbutane along the C2-C3 bond.

Calculation of the energy barrier between the totally eclipsed and anti-conformations of butane.

Importance of understanding potential energy and stability in molecular conformations for practical applications.

Transcripts

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Related Tags

Newman Projections Molecular Stability Chemistry Lesson Ethane Structure Butane Conformations Steric Strain Torsional Energy Organic Chemistry Conformational Analysis Methyl Groups Eclipsed Interactions