Practice Problem: Types of Protons

Professor Dave Explains
24 Jan 201906:01
EducationalLearning
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TLDRThis script explains how to determine the relationship between pairs of protons in molecules by identifying them as homotopic, enantiotopic, diastereotopic, or heterotopic. It uses examples to illustrate the process, including changing hydrogens to other elements to see if new chiral centers or structural isomers are formed, thus highlighting the stereochemistry and symmetry considerations.

Takeaways
  • 🔬 The practice problem involves determining the relationship between pairs of protons in molecules.
  • 🔍 To assess the relationship, the molecule is redrawn in two ways with one hydrogen replaced by another element.
  • 💡 If swapping hydrogens generates a new chiral center with opposite stereochemistry, the protons are diastereotopic.
  • 🔄 For diastereotopic protons, swapping results in diastereomers, which are different in stereochemistry but not in connectivity.
  • 🔄 If the molecule remains the same after swapping hydrogens, the protons are homotopic, indicating they are in equivalent positions.
  • 🔄 Homotopic protons are in the same molecule and can be swapped without changing the molecule's identity.
  • 🌐 In the case of a benzene ring with a bromine, swapping hydrogens for fluorine results in different structural isomers, indicating a heterotopic relationship.
  • 🔄 Heterotopic protons are not equivalent in terms of connectivity, resulting in different structural isomers when swapped.
  • 💠 The presence of a pi bond can make protons enantiotopic by generating a chiral center with opposite stereochemistry.
  • 💠 Enantiotopic protons are non-superimposable mirror images of each other, resulting in enantiomers when swapped.
Q & A

  • What is the purpose of the practice problem discussed in the script?

    -The purpose of the practice problem is to determine the relationship between a pair of protons in molecules, specifically whether they are homotopic, enantiotopic, diastereotopic, or heterotopic.

  • What method is used to assess the relationship between two protons in a molecule?

    -The method involves redrawing the molecule in two ways, swapping one of the hydrogens with another element in each, and observing the resulting changes in the molecule's structure and stereochemistry.

  • What is the significance of generating a new chiral center when swapping a hydrogen with another element?

    -Generating a new chiral center indicates that the swapped molecule is a diastereomer of the original, which means the protons are diastereotopic.

  • How can you determine if the protons are homotopic based on the script?

    -If swapping a hydrogen with another element results in the same molecule (i.e., no new chiral center is formed and the molecule is symmetrical), then the protons are homotopic.

  • What is the relationship between the protons in the example where a benzene ring and a bromine are involved?

    -In the example with a benzene ring and a bromine, changing one hydrogen to fluorine results in different structural isomers, indicating that the protons are heterotopic.

  • Why are the protons in the example with a pi bond considered enantiotopic?

    -The presence of a pi bond makes the molecule chiral. Swapping a hydrogen with another element in this context generates enantiomers, which means the protons have an enantiotopic relationship.

  • What is the difference between diastereotopic and enantiotopic protons?

    -Diastereotopic protons are part of diastereomers, which are stereoisomers that are not mirror images of each other. Enantiotopic protons, on the other hand, are part of enantiomers, which are non-superimposable mirror images of each other.

  • How does the presence of a pi bond affect the relationship between protons in a molecule?

    -A pi bond can introduce chirality to a molecule. If swapping a hydrogen results in a change in the pi bond's position, it can lead to the formation of enantiomers, indicating an enantiotopic relationship.

  • What is the importance of symmetry in determining whether protons are homotopic?

    -Symmetry in a molecule means that swapping a hydrogen with another element does not change the overall structure or stereochemistry. This indicates that the protons are homotopic, as they can be interchanged without affecting the molecule's identity.

  • Can you provide an example from the script where the protons are considered heterotopic?

    -In the script, the example with a benzene ring and a bromine where changing one hydrogen to fluorine results in different structural isomers (meta and para relationships) demonstrates that the protons are heterotopic.

Outlines
00:00
🧪 Understanding Proton Relationships in Molecules

This paragraph introduces a practice problem focused on determining the relationship between pairs of circled protons in molecules. The task is to identify whether these protons are homotopic, enantiotopic, diastereotopic, or heterotopic. The speaker suggests reviewing a tutorial on these terms if not familiar. The example provided involves redrawing a molecule with one hydrogen replaced by chlorine, generating a new chiral center and demonstrating a diastereotopic relationship. The process involves assessing the stereochemistry changes when swapping hydrogens with another element.

Mindmap
Keywords
💡Proton
Protons are subatomic particles that carry a positive charge and are found in the nucleus of atoms. In the context of the video, protons are being discussed in relation to their role in determining the stereochemistry of molecules. The script specifically mentions pairs of protons that are circled in different molecules, which are crucial in identifying the relationship between them.
💡Homotopic
Homotopic protons are those that can be interchanged without changing the overall structure of the molecule. They are essentially indistinguishable in terms of their chemical environment. In the video, the concept is illustrated by replacing a hydrogen with chlorine and noting that the molecule remains the same, indicating that the protons in question are homotopic.
💡Diastereotopic
Diastereotopic protons are those that are not identical and cannot be interchanged without changing the stereochemistry of the molecule. They are part of different stereoisomers. The script explains this by showing that swapping a hydrogen with chlorine in a certain molecule results in a new chiral center and different stereochemistry, thus making the protons diastereotopic.
💡Enantiotopic
Enantiotopic protons are a type of diastereotopic protons that are part of enantiomers, which are non-superimposable mirror images of each other. The video script uses the example of a molecule with a pi bond, where replacing a hydrogen with fluorine results in a molecule that is an enantiomer of the original, indicating that the protons are enantiotopic.
💡Heterotopic
Heterotopic protons are those that are not equivalent in a molecule and are not part of a stereocenter. They are different in terms of their chemical environment. The script demonstrates this by showing that changing a hydrogen to fluorine in a molecule with a benzene ring results in structurally different isomers, indicating a heterotopic relationship.
💡Chiral Center
A chiral center is a point in a molecule where the replacement of any group with another results in a change in the stereochemistry of the molecule. The video script discusses how the introduction of chlorine or fluorine can create a new chiral center, changing the stereochemistry and making the molecules diastereomers.
💡Stereochemistry
Stereochemistry is the aspect of chemistry that deals with the three-dimensional arrangement of atoms in molecules. The video script repeatedly refers to stereochemistry in the context of how the swapping of protons affects the spatial arrangement of molecules, particularly in relation to chiral centers.
💡Chiral Molecule
A chiral molecule is one that cannot be superimposed on its mirror image. The video script uses the example of a molecule with a pi bond, where the introduction of fluorine creates a chiral center, making the molecule chiral and its protons enantiotopic.
💡Meta Relationship
In the context of the video, the meta relationship refers to the position of substituents on a benzene ring. The script discusses how changing a hydrogen to fluorine in a molecule with a benzene ring can result in different meta relationships, indicating a heterotopic relationship between the protons.
💡Pi Bond
A pi bond is a type of covalent bond where the electron density is distributed above and below the plane of the atoms involved. The video script highlights the importance of pi bonds in creating chiral centers, as seen in the example where the introduction of fluorine to a molecule with a pi bond results in a chiral molecule.
💡Structural Isomers
Structural isomers are molecules with the same molecular formula but different structural arrangements of atoms. The script uses the example of changing a hydrogen to fluorine in a molecule with a benzene ring, resulting in different structural isomers, which indicates a heterotopic relationship.
Highlights

Introduction to the practice problem involving determining the relationship of protons in molecules.

Explanation of the need to check out a tutorial on terms like homotopic, enantiotopic, diastereotopic, and heterotopic.

Methodology of redrawing molecules to assess the relationship between protons by swapping hydrogens with other elements.

Example of generating a new chiral center by replacing a hydrogen with chlorine.

Identification of diastereomers based on the change in chirality at a center due to the substitution of hydrogen.

Clarification that the protons in the first example are diastereotopic due to the diastereomer generation.

Illustration of homotopic protons by showing that replacing a hydrogen does not generate a chiral center.

Explanation that the symmetry of the molecule makes the replaced hydrogens homotopic.

Introduction of a benzene ring example with bromine to discuss hydrogen relationships.

Demonstration of heterotopic relationship by changing a hydrogen to fluorine and showing the structural isomerism.

Identification of the structural difference between ortho and meta relationships in the benzene ring example.

Introduction of a pi bond example and its significance in generating a chiral center.

Explanation of how the pi bond affects the relationship of protons, making them enantiotopic.

Demonstration of enantiomers generation by flipping a molecule with a pi bond and fluorine substitution.

Final summary of the relationships: diastereotopic, homotopic, heterotopic, and enantiotopic.

Transcripts

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Related Tags
Molecular ChemistryStereochemistryProton RelationshipsChiral CentersDiastereomersEnantiomersHomotopic ProtonsEnantiotopic ProtonsChemical IsomersMolecular Structure