Chapter 12: Problem 40
How would you prepare the following compounds, starting with cyclopentene and any other reagents needed? (a) Chlorocyclopentane (b) Methylcyclopentane (c) 3-Bromocyclopentene (d) Cyclopentanol (e) Cyclopentylcyclopentane (f) Cyclopenta-1,3-diene
Short Answer
Expert verified
Use hydrohalogenation for (a), Wurtz reaction for (b), allylic bromination for (c), oxymercuration for (d), Friedel-Crafts for (e), and dehydrogenation for (f).
Step by step solution
01
Preparing Chlorocyclopentane
Start with cyclopentene. To convert cyclopentene to chlorocyclopentane, use a hydrohalogenation reaction. Add hydrochloric acid (HCl) to cyclopentene which results in the addition of H and Cl across the double bond, creating chlorocyclopentane.
02
Preparing Methylcyclopentane
Begin with cyclopentene. Perform a free radical halogenation using Cl_2 or Br_2 to form chlorocyclopentane or bromocyclopentane. Next, perform a Wurtz reaction by treating the halogenated product with sodium and methyl chloride (CH_3Cl), substituting the halogen for a methyl group, thus forming methylcyclopentane.
03
Preparing 3-Bromocyclopentene
Use cyclopentene as the starting material and perform allylic bromination. React cyclopentene with N-bromosuccinimide (NBS) under UV light or using a radical initiator to add a bromine atom to the allylic position, resulting in 3-bromocyclopentene.
04
Preparing Cyclopentanol
Start with cyclopentene and perform an oxymercuration-demercuration reaction. First, treat cyclopentene with mercuric acetate (Hg(OAc)_2) and water to form the mercurinium ion intermediate. Then reduce with sodium borohydride (NaBH_4) to form cyclopentanol.
05
Preparing Cyclopentylcyclopentane
Begin with cyclopentene. Transform cyclopentene into cyclopentyl bromide by reacting with HBr. Then perform a Friedel-Crafts alkylation with cyclopentane as the solvent and aluminum chloride (AlCl_3) as a catalyst, forming cyclopentylcyclopentane.
06
Preparing Cyclopenta-1,3-diene
Convert cyclopentene to cyclopenta-1,3-diene via dehydrogenation. Use an oxidizing agent such as selenium dioxide (SeO_2) or sulfur, in the presence of heat, to eliminate hydrogen and form the diene.
Unlock Step-by-Step Solutions & Ace Your Exams!
-
Full Textbook Solutions
Get detailed explanations and key concepts
-
Unlimited Al creation
Al flashcards, explanations, exams and more...
-
Ads-free access
To over 500 millions flashcards
-
Money-back guarantee
We refund you if you fail your exam.
Over 30 million students worldwide already upgrade their learning with Vaia!
Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Hydrohalogenation
Hydrohalogenation is a simple and straightforward reaction in organic chemistry where a hydrogen halide, such as HCl or HBr, is added to an alkene. This process often results in the halide attaching to the more substituted carbon atom, following Markovnikov's rule. When hydrochloric acid is added to cyclopentene, the double bond opens up to allow the addition of hydrogen and chlorine, resulting in the formation of chlorocyclopentane. This reaction is useful for converting alkenes into alkyl halides, which can then be further modified or used in different reactions.
- Hydrogen halide (HX) addition to an alkene.
- Typically follows Markovnikov's rule.
- Used to form alkyl halides from alkenes.
Free Radical Halogenation
Free radical halogenation is an interesting reaction, especially when dealing with alkanes. It involves introducing halogens like Cl_2 or Br_2 to an organic molecule in the presence of UV light or heat, creating free radicals. These radicals are highly reactive species that facilitate the substitution of a hydrogen atom in the organic molecule with a halogen atom. When cyclopentane is treated this way, it forms chlorocyclopentane or bromocyclopentane, which can then undergo further reactions such as the Wurtz reaction to form methylcyclopentane.
- Begins with a radical initiator (UV light or heat).
- Halogen radicals substitute hydrogen atoms.
- Used predominantly with alkanes.
Oxymercuration-Demercuration
Oxymercuration-demercuration is a two-step process used to hydrate alkenes, converting them into alcohols. It begins by adding mercuric acetate and water to the alkene, resulting in a mercurinium ion intermediate. In an aqueous solution, water acts as a nucleophile attacking the more substituted carbon, leading to the opening of the mercurinium bridge. This step is followed by demercuration, where sodium borohydride is used to remove the mercury, yielding the alcohol product. In the case of cyclopentene, this process results in cyclopentanol.
- Two-step reaction: oxymercuration and demercuration.
- Adds water across a double bond, forming an alcohol.
- Regiospecific, often follows Markovnikov's addition.
Friedel-Crafts Alkylation
Friedel-Crafts Alkylation is a classic reaction used to attach alkyl groups to aromatic rings or certain alkenes. This electrophilic aromatic substitution reaction involves an alkyl halide and a Lewis acid catalyst like aluminum chloride (AlCl_3). For instance, to form cyclopentylcyclopentane, cyclopentene is first converted into cyclopentyl bromide using HBr. Then, it undergoes Friedel-Crafts alkylation in the presence of a Lewis acid to bond with another cyclopentane molecule. This reaction is popular for modifying aromatic compounds due to its variety of possible alkylating agents.
- Electrophilic aromatic substitution reaction.
- Utilizes Lewis acids like AlCl_3 as catalysts.
- Common in preparing alkylated aromatic compounds.
Allylic Bromination
Allylic Bromination involves the selective substitution of a hydrogen atom adjacent to a double bond in a molecule with a bromine atom. This is done using N-bromosuccinimide (NBS) under the influence of UV light or a radical initiator. The allylic position is particularly reactive in this context, making it an ideal site for bromination. For example, reacting cyclopentene with NBS targets the allylic position, replacing a hydrogen atom with bromine, thus forming 3-bromocyclopentene. This method is widely used for the regioselective introduction of bromine, facilitating further chemical transformations.
- Targets allylic hydrogen atoms for bromination.
- Requires N-bromosuccinimide (NBS) and UV light.
- Enables regioselective bromine addition.