Textbook Question
For the alkynes shows here, show the product(s) expected to form when treated under the following conditions: (ix) Br2 (2 equiv.). If you expect two products, show both.
(f)
10. Addition Reactions
Alkyne Halogenation
1:51 minutesProblem 61d
Textbook Question
Predict the product(s) that would result when the alkenes shown here are allowed to react under the following conditions: (i) HBr; (ii) HCl; (iii) HBr, H2O2 (iv) H2SO4, H₂O (v) 1. Hg(OAc)2, H2O 2. NaBH4 ; (vi) 1. BH3 2. H2O2, NaOH
(d) 
Verified step by step guidance1
Step 1: Analyze the structure of the given alkene. The molecule contains a double bond, which is the reactive site for electrophilic addition reactions. The double bond is located between the first and second carbon atoms in the chain, and the molecule has stereochemistry at the second carbon.
Step 2: For reaction (i) with HBr, apply Markovnikov's rule. The hydrogen atom from HBr will add to the less substituted carbon of the double bond, while the bromine atom will add to the more substituted carbon. This results in the formation of a bromoalkane.
Step 3: For reaction (ii) with HCl, follow the same Markovnikov addition mechanism as in step 2. The hydrogen atom from HCl will add to the less substituted carbon, and the chlorine atom will add to the more substituted carbon, forming a chloroalkane.
Step 4: For reaction (iii) with HBr and H₂O₂, apply anti-Markovnikov's rule due to the presence of peroxide. The bromine atom will add to the less substituted carbon, and the hydrogen atom will add to the more substituted carbon, forming a bromoalkane with reversed regioselectivity compared to step 2.
Step 5: For reaction (iv) with H₂SO₄ and H₂O, the double bond undergoes hydration via Markovnikov addition. The hydrogen atom adds to the less substituted carbon, and the hydroxyl group (-OH) adds to the more substituted carbon, forming an alcohol.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Electrophilic Addition Reactions
Electrophilic addition reactions are fundamental in organic chemistry, particularly for alkenes. In these reactions, an electrophile reacts with a nucleophile, leading to the formation of a more stable product. For example, when alkenes react with HBr or HCl, the double bond opens up, allowing the halogen to add across the carbon atoms, resulting in haloalkanes.
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Markovnikov's Rule
Markovnikov's Rule is a principle that predicts the regioselectivity of electrophilic addition reactions. It states that when HX (where X is a halogen) adds to an asymmetric alkene, the hydrogen atom will attach to the carbon with the greater number of hydrogen atoms already attached. This rule helps in predicting the major product formed during the reaction.
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Hydroboration-Oxidation
Hydroboration-oxidation is a two-step reaction sequence used to convert alkenes into alcohols. In the first step, BH₃ adds to the alkene in a syn addition, leading to the formation of trialkylborane. The second step involves oxidation with H₂O₂ and NaOH, resulting in the formation of an alcohol. This method is notable for producing alcohols with anti-Markovnikov selectivity.
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