Textbook Question
Rank the following alcohols in order of descending pKa value. Explain your ranking.
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Ch. 4 - Acids and Bases: Electron Flow
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
Chapter 3, Problem 51a
Identify the most stable conjugate base in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer.
(a) 
Verified step by step guidance1
Analyze the electronegativity of the atoms bearing the negative charge. Oxygen (O) is more electronegative than sulfur (S), meaning it can better stabilize a negative charge.
Consider the inductive effect of the trifluoromethyl group (CF₃) attached to the oxygen atom. The CF₃ group is highly electronegative and withdraws electron density through the sigma bond, further stabilizing the negative charge on the oxygen.
Compare the size of the atoms. Sulfur is larger than oxygen, which allows the negative charge to be spread over a larger volume, providing some stabilization. However, this effect is less significant compared to the electronegativity and inductive effects.
Evaluate the overall resonance and delocalization possibilities. In this case, neither structure has resonance stabilization, so this factor does not contribute to the stability comparison.
Weigh the combined effects of electronegativity and inductive stabilization (stronger in the CF₃O⁻ structure) against the size-based stabilization of sulfur. The CF₃O⁻ conjugate base is more stable due to the dominance of electronegativity and inductive effects.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Conjugate Bases
A conjugate base is the species that remains after an acid donates a proton (H+). The stability of a conjugate base is crucial in determining the strength of its corresponding acid; stronger acids have more stable conjugate bases. Factors influencing stability include electronegativity, resonance, and the size of the atom bearing the negative charge.
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Conjugated states
Resonance Stabilization
Resonance stabilization occurs when a molecule can be represented by multiple valid Lewis structures, allowing the negative charge to be delocalized over several atoms. This delocalization reduces electron density on any single atom, enhancing stability. In evaluating conjugate bases, resonance is a key factor, as more resonance structures typically lead to greater stability.
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03:43The radical stability trend.
Electronegativity and Charge Distribution
Electronegativity refers to the ability of an atom to attract electrons in a bond. In the context of conjugate bases, a more electronegative atom stabilizing a negative charge will lead to a more stable conjugate base. When analyzing pairs of conjugate bases, the distribution of charge relative to electronegativity helps determine which base is more stable, as negative charges are better accommodated by more electronegative atoms.
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Related Practice
Textbook Question
Identify the most stable conjugate base in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer.
(f)
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Textbook Question
Identify the most stable conjugate base in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer.
(e)
1625
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Textbook Question
If reacted with a strong base, which of the labeled protons would you expect to be removed first?
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Textbook Question
Rank the following amines in order of their basicity (strongest base = 1 ; weakest base = 6).
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Textbook Question
Identify the most stable conjugate base in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer.
(c)
1160
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