Textbook Question
How many distinct signals would you expect to see in the ¹H NMR spectrum of the following molecules? [Ignore diastereotopic hydrogens for the sake of this assessment.]
(a)
15. Analytical Techniques:IR, NMR, Mass Spect
1H NMR:Number of Signals
Problem 2
Textbook Question
Radical chlorination, a reaction studied in Chapters 5 and 11, replaces a hydrogen with a chlorine. Assuming there is no regioselectivity (all hydrogens can react equally), how many different chloroalkanes are possible upon reaction of each alkane with one equivalent of Cl₂
(a) 
(b) 
(c) 
(d) 
Verified step by step guidance1
Identify the structure of each alkane from the images provided. The first image is cyclohexane, the second is propane, the third is pentane, and the fourth is 2-methylbutane.
For cyclohexane, recognize that all hydrogen atoms are equivalent due to the symmetry of the ring. Therefore, replacing any hydrogen with chlorine will yield the same chloroalkane.
For propane, note that there are two types of hydrogen atoms: those on the terminal carbons and those on the central carbon. Replacing a hydrogen on the terminal carbon will yield 1-chloropropane, while replacing a hydrogen on the central carbon will yield 2-chloropropane.
For pentane, identify the different types of hydrogen atoms based on their positions: terminal, secondary, and tertiary. Each unique position will yield a different chloroalkane upon chlorination.
For 2-methylbutane, consider the different types of hydrogen atoms: those on the primary carbons, secondary carbons, and the tertiary carbon. Each type will result in a different chloroalkane when replaced by chlorine.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Radical Chlorination
Radical chlorination is a chemical reaction where a chlorine atom replaces a hydrogen atom in an alkane. This process involves the formation of free radicals, typically initiated by heat or light, leading to the homolytic cleavage of Cl₂ into two chlorine radicals. These radicals then react with the alkane, abstracting a hydrogen atom and forming a chloroalkane.
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Regioselectivity
Regioselectivity refers to the preference of a chemical reaction to occur at one location over others in a molecule. In the context of radical chlorination, regioselectivity would dictate which hydrogen atoms are more likely to be replaced by chlorine. However, the question assumes no regioselectivity, meaning all hydrogens are equally likely to react, simplifying the analysis of possible products.
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Chloroalkanes
Chloroalkanes are organic compounds where one or more hydrogen atoms in an alkane are replaced by chlorine atoms. The number of different chloroalkanes formed depends on the structure of the original alkane and the positions of the hydrogen atoms. In the absence of regioselectivity, each unique hydrogen position can potentially lead to a different chloroalkane product.
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