Podcast
Questions and Answers
What structural feature distinguishes cis-1,2-dimethylcyclopentane from its trans isomer?
What structural feature distinguishes cis-1,2-dimethylcyclopentane from its trans isomer?
- The orientation of the methyl groups is opposite to each other.
- The two methyl groups are attached to different types of carbon atoms.
- Cis isomers always have fewer hydrogens than trans isomers.
- The methyl groups are oriented toward the same face of the cyclopentane. (correct)
In cis-1-bromo-3-chlorocyclobutane, how are the bromo and chloro substituents oriented?
In cis-1-bromo-3-chlorocyclobutane, how are the bromo and chloro substituents oriented?
- They are both equatorial.
- One is axial and the other is equatorial.
- They are both axial.
- They are located on opposite faces. (correct)
Which of the following statements is true about trans-1-chloro-3-methoxycyclopentane?
Which of the following statements is true about trans-1-chloro-3-methoxycyclopentane?
- The methoxy group and the chloro group face opposite directions. (correct)
- It has a more stable conformation than its cis counterpart.
- It has substituents on the same face of the cyclopentane.
- Both substituents take axial positions.
What is true regarding the axial and equatorial positions in cyclohexane derivatives?
What is true regarding the axial and equatorial positions in cyclohexane derivatives?
Which of the following compounds exhibits cis stereochemistry?
Which of the following compounds exhibits cis stereochemistry?
What is the primary characteristic of conformational isomerism?
What is the primary characteristic of conformational isomerism?
Which conformation of butane is most stable?
Which conformation of butane is most stable?
What is the definition of a dihedral angle in the context of conformational isomerism?
What is the definition of a dihedral angle in the context of conformational isomerism?
In terms of bond arrangement, which of the following describes an eclipsed conformation?
In terms of bond arrangement, which of the following describes an eclipsed conformation?
Which form of ethylene glycol is more stable due to the possibility of intramolecular hydrogen bonding?
Which form of ethylene glycol is more stable due to the possibility of intramolecular hydrogen bonding?
What is the dihedral angle corresponding to an eclipsed conformation?
What is the dihedral angle corresponding to an eclipsed conformation?
Which term describes the conformation where the angle between adjacent bonds is between 0 and 60 degrees?
Which term describes the conformation where the angle between adjacent bonds is between 0 and 60 degrees?
What occurs in a molecule when it is in a staggered conformation?
What occurs in a molecule when it is in a staggered conformation?
What is the primary reason for the formation of geometrical isomers in alkenes?
What is the primary reason for the formation of geometrical isomers in alkenes?
In the E/Z nomenclature system, what does the 'Z' signify?
In the E/Z nomenclature system, what does the 'Z' signify?
Why do cycloalkanes exhibit geometrical isomerism?
Why do cycloalkanes exhibit geometrical isomerism?
What condition must be met for a carbon-carbon double bond to possess geometrical isomers?
What condition must be met for a carbon-carbon double bond to possess geometrical isomers?
Which of the following is an example of a cycloalkane?
Which of the following is an example of a cycloalkane?
In the context of geometrical isomers, what happens when one of the carbons in a double bond has two identical substituents?
In the context of geometrical isomers, what happens when one of the carbons in a double bond has two identical substituents?
When identifying the E/Z isomer of a compound, which rule is used to determine the priority of groups?
When identifying the E/Z isomer of a compound, which rule is used to determine the priority of groups?
What distinguishes cis and trans isomers in cycloalkanes?
What distinguishes cis and trans isomers in cycloalkanes?
Flashcards
Geometric Isomers
Geometric Isomers
Two stereoisomers (diastereomers) have the same molecular formula but differ in spatial arrangement due to restricted rotation around a double bond or in a ring structure.
E/Z Nomenclature
E/Z Nomenclature
The E/Z system helps us name geometric isomers. Z = Zusammen (together). E = Entgegen (opposite). Priority of groups is determined by Cahn-Ingold-Prelog rules.
Cahn-Ingold-Prelog (CIP) Rules
Cahn-Ingold-Prelog (CIP) Rules
A group's priority is determined by its atomic number. The higher the atomic number, the higher the priority.
No geometric isomerism
No geometric isomerism
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Geometric Isomerism in Cycloalkanes
Geometric Isomerism in Cycloalkanes
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Rotation around single bonds
Rotation around single bonds
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Geometric isomers are diastereomers
Geometric isomers are diastereomers
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Different properties of cis and trans isomers
Different properties of cis and trans isomers
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Cis/Trans Isomers
Cis/Trans Isomers
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Cis Isomers
Cis Isomers
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Trans Isomers
Trans Isomers
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Axial Substituents
Axial Substituents
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Equatorial Substituents
Equatorial Substituents
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Conformational Isomerism
Conformational Isomerism
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Rotamers
Rotamers
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Dihedral Angle
Dihedral Angle
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Eclipsed Conformation
Eclipsed Conformation
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Staggered Conformation
Staggered Conformation
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Anti Conformation
Anti Conformation
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Gauch Conformation
Gauch Conformation
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Skew Conformation
Skew Conformation
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Study Notes
2- Geometrical Isomerism
- Stereoisomers (diastereomers) have the same molecular formula but different spatial arrangements.
- This difference arises due to restricted rotation around either double bonds (in alkenes) or the bonds within cyclic structures (in cycloalkanes).
- Open-chain alkanes can rotate freely around their C-C single bonds.
- Alkenes and cycloalkanes exhibit restricted rotation.
- The two stereoisomers (geometric isomers) have distinct physical and chemical properties.
Example
- Cis-dichloroethene and trans-dichloroethene are examples of geometric isomers. They differ in the arrangement of chlorine atoms around the double bond.
Z/E Nomenclature
- Used to identify geometric isomers of alkenes with different groups bonded to the double-bonded carbons.
- 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.
- Priority is determined using Cahn-Ingold-Prelog rules.
Examples (Z & E)
- Specific examples of molecules are shown where geometric isomers are given as Z or E in the provided text.
Geometrical Isomers in Cyclic Compounds
- Cycloalkanes exhibit restricted rotation around C-C bonds, similar to alkenes.
- Substituents can be on the same side (cis) or opposite sides (trans).
No Geometrical Isomers
- If one carbon of a double bond has two identical substituents, there are no geometric isomers.
3- Conformational Isomerism (Rotamers)
- Conformational isomerism is a form of stereoisomerism where isomers interconvert due to rotation around single bonds.
- These isomers are also known as conformers or rotamers.
- The position of atoms change with rotation.
Types of Conformational Isomers
- Staggered: Carbon-hydrogen bonds are as far apart as possible.
- Eclipsed: Carbon-hydrogen bonds are directly aligned.
Dihedral Angle
- Angle between bonds on adjacent atoms.
- Eclipsed is 0°.
- Staggered is 60°.
Important Concepts
- Conformers of Butane: Specific examples detailing different conformations of butane are shown, highlighting anti, gauche, and eclipsed forms.
- Stability of Conformers: Most stable conformations are ones where bulky groups are as far apart as possible (staggered or anti).
- Intramolecular Hydrogen Bonding: This can enhance stability in certain conformations (e.g., gauche form of ethylene glycol).
- Newman Projections: Used to represent the conformations of molecules.
- Torsional Strain: Strain associated with eclipsing bonds.
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