Textbook Question
For each pair of compounds, predict the one with a higher boiling point. Which compounds have zero dipole moments?
c. cyclohexene or 1,2-dichlorocyclohexene
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Ch. 7 - Structure and Synthesis of Alkenes; Elimination
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 7, Problem 11a
For each pair of compounds, predict the one with a higher boiling point. Which compounds have zero dipole moments?
a. cis-1,2-dichloroethene or cis-1,2-dibromoethene
Verified step by step guidance1
Step 1: Understand that boiling point is influenced by molecular weight and intermolecular forces. Compounds with stronger intermolecular forces or higher molecular weights generally have higher boiling points.
Step 2: Compare the molecular weights of cis-1,2-dichloroethene and cis-1,2-dibromoethene. Bromine is heavier than chlorine, so cis-1,2-dibromoethene has a higher molecular weight.
Step 3: Consider the types of intermolecular forces present. Both compounds have dipole-dipole interactions due to the polar C-Cl and C-Br bonds, but the heavier bromine atoms in cis-1,2-dibromoethene contribute to stronger London dispersion forces.
Step 4: Predict that cis-1,2-dibromoethene will have a higher boiling point due to its higher molecular weight and stronger London dispersion forces.
Step 5: Determine the dipole moment. Both compounds are cis isomers, which means they have a net dipole moment due to the asymmetrical arrangement of the polar bonds. Therefore, neither compound has a zero dipole moment.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Boiling Point and Intermolecular Forces
The boiling point of a compound is influenced by the strength of its intermolecular forces. Stronger forces, such as hydrogen bonding, dipole-dipole interactions, and London dispersion forces, result in higher boiling points. In comparing similar compounds, the size and polarizability of the molecules can also affect the boiling point, with larger, more polarizable molecules typically having higher boiling points.
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How IMFs are related to melting and boiling points.
Dipole Moment
A dipole moment occurs in a molecule when there is an uneven distribution of electron density, resulting in a partial positive and negative charge. Molecules with symmetrical structures, like trans isomers, often have zero dipole moments because the individual bond dipoles cancel each other out. In contrast, asymmetrical molecules, such as cis isomers, usually have a net dipole moment due to the non-cancellation of bond dipoles.
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01:46How dipole-dipole forces work.
Cis and Trans Isomerism
Cis and trans isomerism is a type of stereoisomerism where molecules have the same formula but differ in the spatial arrangement of atoms around a double bond. In cis isomers, similar groups are on the same side of the double bond, often resulting in a net dipole moment. Trans isomers have similar groups on opposite sides, which can lead to a cancellation of dipole moments, affecting properties like boiling point and solubility.
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Related Practice
Textbook Question
How many stereogenic double bonds are in octa-1,3,5-triene? How many stereocenters are there? Draw and name the four stereoisomers of octa-1,3,5-triene.
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Textbook Question
For each pair of compounds, predict the one with a higher boiling point. Which compounds have zero dipole moments?
b. cis- or trans-2,3-dichlorobut-2-ene
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Textbook Question
Draw the six stereoisomers of octa-2,4,6-triene. Explain why there are only six stereoisomers, rather than the eight we might expect for a compound with three stereogenic double bonds.
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Textbook Question
Teflon-coated frying pans routinely endure temperatures that would cause polyethylene or polypropylene to oxidize and decompose. Decomposition of polyethylene is initiated by free-radical abstraction of a hydrogen atom by O2. Bond-dissociation energies of C—H bonds are about 400 kJ/mol, and C—F bonds are about 460 kJ/mol. The BDE of the H—OO bond is about 192 kJ/mol, and the F—OO bond is about 63 kJ/mol. Show why Teflon (Figure 7-5) is much more resistant to oxidation than polyethylene is.
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Textbook Question
Use the data in Table 7-2 to predict the energy difference between 2,3-dimethylbut-1-ene and 2,3-dimethylbut-2-ene. Which of these double-bond isomers is more stable?
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