Ch. 11 - Radical ReactionsSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins

Radicals are unstable intermediates. So we’re going to have to discuss some ways to stabilize them. 

Concept #1: The radical stability trend.  

Unlike carbocations, allylic and benzylic radicals are ALWAYS most stable.

Determine which of the following radicals is the most stable.   

Example #1: Determine which of the following radicals is the most stable.   

Additional Problems
Which radical is the least stable?
Identify the most stable and least stable radical of the following.    Most stable          Least stable         
Rank the following carbon radicals according to their increasing stability. (least stable most stable) A. 1, 4, 3, 2 B. 1, 4, 2, 3 C. 2, 3, 1, 4 D. 3, 4, 2, 1 E. 4, 1, 2, 3 F. 3, 2, 1, 4
For which free radical can the most resonance forms be written that show the delocalization of the radical?  
Photochemical chlorination of pentane gave a mixture of three isomeric monochlorides. The principal monochloride constituted 46% of the total, and the remaining 54% was approximately a 1:1 mixture of the other two isomers. Write structural formulas for the three monochloride isomers and specify which one was formed in greatest amount. (Recall that a secondary hydrogen is abstracted three times faster by a chlorine atom than a primary hydrogen.) 
Which of the following radicals is the most likely to form during the propagation phase of a radical chain reaction?  
Which is the most stable radical?
For each of the following, choose the best answer (give the letter).   (i) Which one has the smaller heat of hydrogenation: (a) 1-methylcyclohexene or (b) 3-methylcyclohexene? (ii) Which one has the larger heat of combustion: (a) (E)-cyclononene or (b) (Z)-cyclononene? (iii) Which one is a concerted reaction: (a) acid-catalyzed dehydration of an alcohol; (b) reaction of a tertiary alkyl chloride with potassium tert-butoxide; or (c) addition of Cl 2 to an alkene? (iv) Which one is thermodynamically more stable: (a) isobutyl radical or (b) tert-butyl radical? (v) Which one is the rate law for an E2 reaction of an alkyl halide: (a) rate = k[RX] or (b) rate = k[RX][base]? (vi) The major product of the reaction of methylcyclopentane with Br 2 in the presence of heat and light is which of the following type of alkyl bromide: (a) primary; (b) secondary; or (c) tertiary? (vii) The major product of the reaction of 1-pentene with HBr in the presence of peroxides and heat is formed via which of the following: (a) a secondary carbocation; (b) a secondary radical; or (c) a secondary carbanion? (viii) Stereoisomers that are not mirror images of each other and are not superimposable are: (a) diastereomers; (b) enantiomers; (c) conformers; (d) polymers. 
List the stability of different kinds of radicals: 1°, 2°, 3° and methyl radicals. Why? (Use only one word/terminology to explain)
At which of the positions would the bromine radical react at the fastest rate?  
Circle the most easily abstracted hydrogen (H a, H b, Hc, or H d) in free radical bromination and explain why.
Rank the following radicals in order of stability (1 = most stable, 4 = least stable).
Which of the following is the most stable radical?  
What is the hybridization of the carbon that bears the unpaired electron in the vinyl radical?In which type of orbital does the unpaired electron reside?
In the molecule shown below, determine which of the labeled bonds is expected to have the lowest bond dissociation energy.  
Following intermediates place in the order of increasing stability (1- least stable, 3- most stable intermediate)
Which alkane-alkene pair would be formed by a disproportionation reaction of the two radicals produced by the most energetically favored homolytic bond cleavage in the molecule shown?
Rank the following radicals in order of decreasing stability.