Textbook Question
The radical fluorination of 2-methyl propane resulted in a 14:86 ratio of products.
(a) On the basis of this ratio, calculate the relative reactivity of 1° and 3° C―H bonds in the radical fluorination.
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Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics
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. 5 - Chemical Reaction Analysis: Thermodynamics and KineticsProblem 42
Mullins 1st EditionCh. 5 - Chemical Reaction Analysis: Thermodynamics and KineticsProblem 42Chapter 4, Problem 42
Given the ratio of products obtained in the bromination of propane, calculate the relative reactivity of a 1° C–H bond to a 2° C–H bond under these conditions.
Verified step by step guidance1
Step 1: Analyze the given data. The bromination of propane produces two products: 2-bromopropane (97%) and 1-bromopropane (3%). This indicates that bromination occurs preferentially at the secondary (2°) carbon over the primary (1°) carbon.
Step 2: Determine the number of equivalent hydrogen atoms available for substitution at each type of carbon. Propane has 6 primary (1°) hydrogens and 2 secondary (2°) hydrogens.
Step 3: Calculate the product formation per hydrogen type. Divide the percentage yield of each product by the number of hydrogens of the corresponding type. For 2-bromopropane, divide 97% by 2 hydrogens. For 1-bromopropane, divide 3% by 6 hydrogens.
Step 4: Compare the relative reactivity of the 1° C–H bond to the 2° C–H bond. The relative reactivity is the ratio of the product formation per hydrogen type for the secondary hydrogens to the primary hydrogens.
Step 5: Interpret the result. A higher relative reactivity for the 2° C–H bond indicates that bromination is more favorable at the secondary carbon under these conditions.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Bromination Mechanism
Bromination of alkanes involves a free radical mechanism where bromine (Br2) is homolytically cleaved to form bromine radicals. These radicals then abstract hydrogen atoms from the alkane, leading to the formation of alkyl radicals. The stability of these alkyl radicals influences the product distribution, as more stable radicals will form preferentially.
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00:54
Mechanism of Allylic Bromination.
Reactivity of C-H Bonds
The reactivity of C-H bonds in alkanes varies based on the degree of substitution of the carbon atom to which the hydrogen is attached. Primary (1°) C-H bonds are less reactive than secondary (2°) C-H bonds due to the stability of the resulting radicals; 2° radicals are more stable than 1° radicals, leading to a higher likelihood of bromination at 2° sites.
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Product Ratio and Relative Reactivity
The ratio of products formed during bromination reflects the relative reactivity of the different C-H bonds. By analyzing the product distribution, one can deduce the relative reactivity of 1° versus 2° C-H bonds. A higher proportion of products from 2° bromination compared to 1° indicates that 2° C-H bonds are more reactive under the given conditions.
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04:32Explaining relative rates of halogenation.
Related Practice
Textbook Question
The following are all substitution reactions, two of which we study in later chapters. With no knowledge of mechanism, what would you expect the ratio of products to be for each reaction, based on a random statistical distribution?
(b) Replacing a hydrogen (H) with bromine (Br):
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Textbook Question
Through the course of this chapter, we have discussed only alkane chlorination and bromination, yet there are two other halogens we have not discussed.
(b) Is radical iodination a favorable reaction? Do you expect it to be selective? Show your calculations.
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Textbook Question
The following are all substitution reactions, two of which we study in later chapters. With no knowledge of mechanism, what would you expect the ratio of products to be for each reaction, based on a random statistical distribution?
(a) Replacing a hydrogen (H) with deuterium (D):
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Textbook Question
The radical fluorination of 2-methyl propane resulted in a 14:86 ratio of products.
(b) From the relative reactivity, calculate the difference in energy between the transition states of the first propagation steps leading to a 1° and 3° radical.
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Textbook Question
The following are all substitution reactions, two of which we study in later chapters. With no knowledge of mechanism, what would you expect the ratio of products to be for each reaction, based on a random statistical distribution?
(a) Replacing a hydrogen (H) with chlorine (Cl):
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