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Questions and Answers
Which of the following compounds is classified as 'cis'?
Which of the following compounds is classified as 'cis'?
- trans-1-chloro-3-methoxycyclopentane
- trans-1,2-dimethylcyclopentane
- trans-1-bromo-3-chlorocyclobutane
- cis-1,2-dimethylcyclopentane (correct)
Trans-1-bromo-3-chlorocyclobutane has substituents on the same side of the cyclobutane ring.
Trans-1-bromo-3-chlorocyclobutane has substituents on the same side of the cyclobutane ring.
False (B)
What geometrical configuration is indicated when substituents point toward opposite faces?
What geometrical configuration is indicated when substituents point toward opposite faces?
trans
The compound _______ features an equatorial bromo substituent.
The compound _______ features an equatorial bromo substituent.
Match the compound with its configuration:
Match the compound with its configuration:
What is the primary reason for geometrical isomerism in alkenes?
What is the primary reason for geometrical isomerism in alkenes?
Cyclic compounds can have geometrical isomers due to restricted rotation.
Cyclic compounds can have geometrical isomers due to restricted rotation.
What are the designations used in the E/Z nomenclature system?
What are the designations used in the E/Z nomenclature system?
Cis-dichloroethene and trans-dichloroethene are examples of __________ isomers.
Cis-dichloroethene and trans-dichloroethene are examples of __________ isomers.
Match the following terms with their definitions:
Match the following terms with their definitions:
Which condition does NOT lead to geometrical isomerism?
Which condition does NOT lead to geometrical isomerism?
The priority of groups in the E/Z nomenclature is determined using the Cahn-Ingold-Prelog rules.
The priority of groups in the E/Z nomenclature is determined using the Cahn-Ingold-Prelog rules.
What is an example of a cycloalkane?
What is an example of a cycloalkane?
Which type of isomerism is characterized by isomers that can be interconverted exclusively by rotations about single bonds?
Which type of isomerism is characterized by isomers that can be interconverted exclusively by rotations about single bonds?
The staggered conformation is the least stable conformation of butane.
The staggered conformation is the least stable conformation of butane.
What is the dihedral angle in molecular structure?
What is the dihedral angle in molecular structure?
The _____ conformation of ethylene glycol is more stable due to intramolecular hydrogen bonding.
The _____ conformation of ethylene glycol is more stable due to intramolecular hydrogen bonding.
Match the type of conformation with its description:
Match the type of conformation with its description:
Which conformation has a dihedral angle of 0 degrees?
Which conformation has a dihedral angle of 0 degrees?
Conformational isomers are typically called rotamers.
Conformational isomers are typically called rotamers.
What is the most stable conformation of butane?
What is the most stable conformation of butane?
Flashcards
Stereoisomers
Stereoisomers
Isomers that have the same connectivity but differ in their spatial arrangement.
Enantiomers
Enantiomers
Stereoisomers that are non-superimposable mirror images of each other.
Diastereomers
Diastereomers
Stereoisomers that are not mirror images of each other.
Cis Isomer
Cis Isomer
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Trans Isomer
Trans Isomer
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Geometrical Isomers
Geometrical Isomers
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Z Isomer
Z Isomer
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E Isomer
E Isomer
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Cahn-Ingold-Prelog Rules
Cahn-Ingold-Prelog Rules
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No Geometrical Isomers
No Geometrical Isomers
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Cycloalkanes
Cycloalkanes
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Conformational Isomers
Conformational Isomers
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Eclipsed Conformation
Eclipsed Conformation
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Staggered Conformation
Staggered Conformation
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Skew Conformation
Skew Conformation
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Dihedral Angle
Dihedral Angle
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Anti Conformation of Butane
Anti Conformation of Butane
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Gauche Conformation
Gauche Conformation
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Conformational Isomerism
Conformational Isomerism
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Study Notes
2- Geometrical Isomerism
- Stereoisomers (diastereomers) have the same molecular formula but differ in spatial arrangement.
- This difference arises due to either restricted rotation around double bonds (in alkenes) or restricted rotation in cyclic structures (in cycloalkanes).
- Open-chain alkanes rotate freely about single bonds.
- Alkenes and cycloalkanes exhibit restricted rotation.
- Cis- and trans- isomers have different physical and chemical properties.
Example of Geometrical Isomers
- Cis-dichloroethene and trans-dichloroethene are examples of geometrical isomers.
- The difference lies in the arrangement of chlorine atoms around the double bond.
Z/E Nomenclature
- Used to name geometrical isomers with different groups on a double bond.
- Z (Zusammen): Higher priority groups are on the same side of the double bond.
- E (Entgegen): Higher priority groups are on opposite sides of the double bond.
- Cahn-Ingold-Prelog rules determine priority.
Examples of Z/E isomers
- Specific examples of molecules with Z/E configurations were given with priority rules.
Geometrical Isomers in Cyclic Compounds
- Cycloalkanes are cyclic alkanes with restricted rotation around carbon-carbon bonds.
- Cis- and trans- descriptors indicate relative positions of substituents on the ring relative to the ring plane.
- Cis: substituents are on the same side of the ring
- Trans: substituents are on opposite sides of the ring
Examples of Cis/Trans isomers in cyclic compounds
- Specific examples of cyclic compounds with cis and trans isomers were shown.
No Geometrical Isomers
- If one carbon of a double bond has two identical substituents, there are no geometrical isomers.
3 - Conformational Isomerism (Rotamers)
- Conformational isomerism is a form of stereoisomerism where isomers interconvert solely via rotation about single bonds.
- These isomers are also known as conformers or rotamers.
Types of Conformational Isomers in Ethane
- Eclipsed: C-H bonds are directly aligned.
- Staggered: C-H bonds are maximally separated.
What is a Dihedral/Torsional Angle
- The angle between C-H bonds on adjacent carbons in a Newman projection.
- In an eclipsed conformation, the dihedral angle is 0°.
- In a staggered conformation, the dihedral angle is 60°.
- Skew conformations have intermediate dihedral angles.
Conformations of Butane
- The different conformations of butane (e.g., anti, gauche, eclipsed) were shown.
- Staggered conformations (e.g., anti) are generally more stable than eclipsed conformations due to reduced steric hindrance.
Most Stable Conformers
- The most stable conformers maximize the distance between bulky groups.
- Intramolecular forces like hydrogen bonding can increase the stability of certain conformations in specific molecules.
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