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Chapter 2: Problem 7

What are the products formed when buta-1, 3 -diene is treated with HBr in \(1: 1\) molar proportion? Explain the formation of the products.

Short Answer

Expert verified
Answer: The major product is 3-bromo-1-butene.

Step by step solution

01

Identify the reaction mechanism

Buta-1,3-diene is a conjugated diene, which means the double bonds are separated by a single bond. Conjugated dienes commonly undergo electrophilic addition reactions due to the presence of multiple pi bonds. In this case, the electrophile is HBr, and the reaction is an electrophilic addition to the diene.
02

Consider regioselectivity to predict the possible products

Conjugated dienes exhibit regioselectivity when reacting with electrophiles, which means the electrophile can add to different carbons of the diene, yielding different products. In this case, there are two possible products: 3-bromo-1-butene and 1-bromo-2-butene.
03

Evaluate the stability of the carbocations formed during the reaction

The stability of carbocations is crucial in determining the major product in the electrophilic addition of HBr to buta-1,3-diene. If the carbocation is more stable, it is more likely to form from the initial attack of the hydrogen to the pi bond. For 3-bromo-1-butene, the intermediate carbocation would be on the second carbon, which is an allylic carbocation. Allylic carbocations are resonance stabilized and thus more stable than non-allylic carbocations. For 1-bromo-2-butene, the intermediate carbocation would be on the third carbon, which is not an allylic carbocation, and less stable than the carbocation formed in the other pathway.
04

Identify the major product

Based on the regioselectivity and the stability of the intermediate carbocations, the major product of the reaction between buta-1,3-diene and HBr in a 1:1 molar proportion is 3-bromo-1-butene, which forms through a more stable allylic carbocation.

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Most popular questions from this chapter

HI does not exhibit peroxide effect because (a) HI is a reducing agent. (b) the iodine free radicals formed recombine readily to form the iodine molecule. (c) the bond energy of HI is very high that it does not undergo homolytic fission to give iodine radicals. (d) Free radical reactions work well when both the propagation steps are endothermic.

\(\mathrm{HBr}\) reacts with \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{OCH}_{3}\) in the absence of peroxides to give mainly (a) \(\mathrm{BrCH}_{2} \mathrm{CHO}\) and \(\mathrm{CH}_{3} \mathrm{OH}\) (b) \(\mathrm{BrCH}_{2}-\mathrm{CH}_{2}-\mathrm{OCH}_{3}\) (c) \(\mathrm{H}_{3} \mathrm{C}-\mathrm{CHBr}-\mathrm{OCH}_{3}\) (d) \(\mathrm{CH}_{3} \mathrm{CHO}\) and \(\mathrm{CH}_{3} \mathrm{Br}\)

Which group or atom in each of the following pairs gets priority according to CIP rules used for assigning \(\mathrm{R}\) and \(\mathrm{S}\) configuration for chiral molecules? (a) \(-\mathrm{CH}_{2} \mathrm{OH}\) or \(-\mathrm{CH}_{2} \mathrm{Cl}\) (b) \(-\mathrm{CH}=\mathrm{CH}_{2}\) or \(-\mathrm{CH}_{2} \mathrm{CH}_{3}(\mathrm{c})-\mathrm{NH}_{2}\) or \(-\mathrm{OH}\) (d) \(-\mathrm{CH}_{2} \mathrm{OH}\) or \(-\mathrm{CHO}\) Choose from the options given below \(\begin{array}{llll}\text { (a) } \mathrm{A}:-\mathrm{CH}_{2} \mathrm{OH}, & \mathrm{B}:-\mathrm{CH}=\mathrm{CH}_{2}, & \mathrm{C}:-\mathrm{NH}_{2}, & \mathrm{D}:-\mathrm{CHO}\end{array}\) \(\begin{array}{llll}\text { (b) } \mathrm{A}:-\mathrm{CH}_{2} \mathrm{Cl}, & \mathrm{B}:-\mathrm{CH}=\mathrm{CH}_{2}, & \mathrm{C}:-\mathrm{OH}, & \mathrm{D}:-\mathrm{CHO}\end{array}\) \(\begin{array}{llll}\text { (c) } \mathrm{A}:-\mathrm{CH}_{2} \mathrm{OH}, & \mathrm{B}:-\mathrm{CH}_{2} \mathrm{CH}_{3}, & \mathrm{C}:-\mathrm{NH}_{2}, & \mathrm{D}:-\mathrm{CHO}\end{array}\) \(\begin{array}{llll}\text { (d) } \mathrm{A}:-\mathrm{CH}_{2} \mathrm{Cl}, & \mathrm{B}:-\mathrm{CH}_{2}-\mathrm{CH}_{3}, & \mathrm{C}:-\mathrm{OH}, & \mathrm{D}:-\mathrm{CH}_{2} \mathrm{OH}\end{array}\)

Alkanes and alkenes can be prepared by (a) Wurtz reaction (b) Williamson synthesis (c) Dehydrohalogenation (d) Kolbe's electrolysis

A reaction that does not lead to an alkene is (a) Kolbe's electrolysis (b) \(\alpha\) -elimination (c) Wittig reaction (d) dehalogenation
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