Textbook Question
Looking ahead in Chapter 4, we explain that molecules like CH3+ are Lewis acids or electron pair acceptors. Into which orbital would the new electron pair go?
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Ch. 2 - General Chemistry Translated: Finding the Electrons
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471
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Table of contents
- Ch. 2 - General Chemistry Translated: Finding the Electrons114
- Ch. 3 - Alkanes and Cycloalkanes: Properties and Conformational Analysis109
- Ch. 4 - Acids and Bases: Electron Flow144
- Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics118
- Ch. 6 - Stereoisomerism: Arrangement of Atoms in Space112
- Ch. 7 - Principles of Green (Organic) Chemistry3
- Ch. 8 - Alkenes I: Properties and Electrophilic Additions158
- Ch. 9 - Alkenes II: Oxidation and Reduction150
- Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions101
- Ch. 11 - Properties and Synthesis of Alkyl Halides: Radical Reactions108
- Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes172
- Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination239
- Ch. 14 - Structural Identification I: Infrared Spectroscopy and Mass Spectrometry54
- Ch. 15 - Structural Identification II: Nuclear Magnetic Resonance Spectroscopy93
- Ch. 16 - Metals in Organic Chemistry48
- Ch. 17 - Carbonyl Addition Reactions: Aldehydes and Ketones45
- Ch. 18 - Nucleophilic Acyl Substitution I: Carboxylic Acids18
- Ch. 19 - Nucleophilic Acyl Substitution II: Carboxylic Acid Derivatives39
- Ch. 20 - Enolates: Carbonyl Addition and Substitution13
- Ch. 21 - Conjugated Systems I: Stability and Addition Reactions56
- Ch. 22 - Conjugated Systems II: Pericyclic Reactions54
- Ch. 23 - Benzene I: Aromatic Stability and Substitution Reactions64
- Ch. 24 - Benzene II: Reactions Influenced by the Aromatic Ring62
- Ch. 25 - Amines: Structure, Reactions, and Synthesis27
- Ch. 26 - Amino Acids, Proteins, and Peptide Synthesis9
- Ch. 27 - Carbohydrates, Nucleic Acids, and Lipids54
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
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Mullins 1st EditionCh. 2 - General Chemistry Translated: Finding the ElectronsProblem 79
Mullins 1st EditionCh. 2 - General Chemistry Translated: Finding the ElectronsProblem 79Chapter 1, Problem 79
There is free rotation around the C―C bond in ethane. There is an extremely high barrier to rotation around the C=C bond in in ethene. Explain.
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In ethane (C₂H₆), the carbon-carbon bond is a single bond (sigma bond, denoted as σ). A sigma bond is formed by the head-on overlap of atomic orbitals, and it allows for free rotation around the bond axis because the electron density is symmetrically distributed along the bond axis.
In ethene (C₂H₄), the carbon-carbon bond is a double bond, consisting of one sigma bond (σ) and one pi bond (π). The sigma bond is formed by the head-on overlap of orbitals, while the pi bond is formed by the side-by-side overlap of p orbitals above and below the plane of the atoms.
The pi bond in ethene restricts rotation because the side-by-side overlap of the p orbitals would be disrupted if the carbon atoms were to rotate relative to each other. This disruption would break the pi bond, which requires significant energy to overcome.
The energy barrier to rotation around the C=C bond in ethene is extremely high due to the strength of the pi bond. In contrast, the single sigma bond in ethane does not have this restriction, allowing for free rotation.
In summary, the free rotation in ethane is due to the single sigma bond, while the restricted rotation in ethene is due to the presence of the pi bond in the double bond, which prevents rotation without breaking the bond.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
C―C Bond Rotation
In ethane, the C―C bond is a single bond, allowing for free rotation around the bond axis. This rotation occurs because single bonds have sigma (σ) bonds formed by the head-on overlap of orbitals, which do not have any significant energy barriers to rotation. As a result, the spatial arrangement of the atoms can change freely without breaking the bond.
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Single bonds, double bonds, and triple bonds.
C=C Bond Characteristics
In contrast, the C=C bond in ethene is a double bond, consisting of one sigma (σ) bond and one pi (π) bond. The pi bond is formed by the side-to-side overlap of p orbitals, which restricts rotation because breaking the pi bond requires significant energy. This results in a high barrier to rotation around the C=C bond, leading to fixed geometries in the molecule.
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Energy Barriers in Bond Rotation
The energy barrier to rotation around a bond is influenced by the type of bond and the presence of substituents. In ethene, the pi bond creates a substantial energy barrier that must be overcome to rotate the molecule, while in ethane, the absence of such a barrier allows for unrestricted rotation. Understanding these energy dynamics is crucial for predicting molecular behavior and reactivity.
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Related Practice
Textbook Question
The C―H σ bond length in ethane is 1.09 Å. The C―H σ bond in ethene is 1.07 Å. Explain.
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Textbook Question
In propene, the indicated C―C bond length is 1.51 Å. In the allyl cation, the indicated C―C bond length is 1.41 Å. Explain.
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Textbook Question
Carbon dioxide (CO2) has no dipole moment (μ = 0 D). The related molecule sulfur dioxide (SO2) does have a dipole moment (μ = 1.6 D) Explain this observation.
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Textbook Question
Given the Lewis structures, indicate the direction of the dipole moment, if there is one.
(b)
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Textbook Question
Given the Lewis structures, indicate the direction of the dipole moment, if there is one.
(e)
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