Solving Alkene Reactions Problems for Chem Exam

In summary, you are studying for a chem exam and you are having difficulty solving some problems. You are unsure of how to proceed with certain problems. Some of the questions you are unsure of have answers that can be found by looking at the mechanism of the reactions. You also ask for help in answering some of your questions, but unfortunately you are too late. If you had gone earlier in the morning, your professor may have been able to help you. He or she may have been able to tell you what the intermediate in the halogenation reaction was. Additionally, he or she may have been able to tell you how you did on the test. Good luck on your upcoming exam!
  • #1
ChemDoodle
25
0
Hey I'm studying for my chem exam & I am having difficulty solving some problems.

1. 1,3cyclohexadiene + Br2= ?
Here,should i treat it like a conjugated diene? Meaning that the Br molecules will have 1,2 and 1,4 additions on the diene and 2 products will be there?

2. 1,4cyclohexadiene + Br2 = ?
Here should i t eat it like an isolated diene? & if so..where should the Br add? On which bond? Or will there be 2 products? With Br adding on the 1 double bond in the first & 4 double bond in the second?

3. When propylene is treated with bromine in methanol (CH3OH),two products are formed C3H6Br2 & C4H9BrO.Explain meachanistically how each are formed.
Here,the first product is simple..its obtained by halogenation of alkenes..simple addition of the Br molecules on the pi-bond.But i wasn't able to determine how the second product is obtained? Obviously methanol has something to do with it..But what kind of reaction is it? We studied hyrohalogenation but nothing about alcohols & halogens together.

4. 1,2-dimethylcyclopentene + BH3 + H2O2/NaOH =
This gives us the same product as direct hydrolysis since the alkene is symmetrical,correct?

Any help in these questions would be greatly appreciated.They are just doubts that need clarifying :) & my exam is tomorrow.
 
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  • #2
Anyone,please? :(
 
  • #3
I guess I'm too late to help you for your exam. How did you do on the test? You were right about some of these.
 
  • #4
ChemDoodle said:
Hey I'm studying for my chem exam & I am having difficulty solving some problems.

1. 1,3cyclohexadiene + Br2= ?
Here,should i treat it like a conjugated diene? Meaning that the Br molecules will have 1,2 and 1,4 additions on the diene and 2 products will be there?

2. 1,4cyclohexadiene + Br2 = ?
Here should i t eat it like an isolated diene? & if so..where should the Br add? On which bond? Or will there be 2 products? With Br adding on the 1 double bond in the first & 4 double bond in the second?

3. When propylene is treated with bromine in methanol (CH3OH),two products are formed C3H6Br2 & C4H9BrO.Explain meachanistically how each are formed.
Here,the first product is simple..its obtained by halogenation of alkenes..simple addition of the Br molecules on the pi-bond.But i wasn't able to determine how the second product is obtained? Obviously methanol has something to do with it..But what kind of reaction is it? We studied hyrohalogenation but nothing about alcohols & halogens together.

4. 1,2-dimethylcyclopentene + BH3 + H2O2/NaOH =
This gives us the same product as direct hydrolysis since the alkene is symmetrical,correct?

Any help in these questions would be greatly appreciated.They are just doubts that need clarifying :) & my exam is tomorrow.

1) Probably condition dependent. I have seen both 1,4 and 1,2 addition in similar cases.

2) Try drawing the mechanism, and see if you can get addition to both double bonds with one equivalent.

3) What is the intermediate in halogenation?

4) As per your previous thread, if we assume the lack of locant for the ene means it's a 1-ene. I'm not sure you get hydrolysis.
 
  • #5
chemisttree said:
I guess I'm too late to help you for your exam. How did you do on the test? You were right about some of these.

86,highest grade :P I went early the next day & asked my prof about them hehe.
Thanx tho :D
 

1. What are the steps for solving alkene reactions problems for a chemistry exam?

The steps for solving alkene reactions problems for a chemistry exam are as follows:

  • Identify the type of reaction (e.g. addition, elimination, substitution)
  • Determine the reactants and products
  • Balance the chemical equation
  • Identify the reagents and their roles (e.g. acid, base, catalyst)
  • Apply the appropriate reaction mechanism and draw the intermediate steps
  • Predict the major and minor products
  • Check for any stereochemistry or regiochemistry considerations
  • Calculate the energy changes of the reaction (e.g. enthalpy, entropy)

2. How do I identify the reagents and their roles in an alkene reaction problem?

The reagents and their roles in an alkene reaction problem can be identified by carefully reading the reaction conditions and understanding the reaction mechanism. For example, an acid catalyst indicates an addition reaction, while a base catalyst indicates an elimination reaction. Additionally, knowing the general properties of reagents (e.g. nucleophile, electrophile) can help in identifying their roles in the reaction.

3. How do I determine the major and minor products in an alkene reaction problem?

The major and minor products in an alkene reaction problem can be determined by considering the stability of the intermediate and transition states. The more stable the intermediate or transition state, the more likely it is to form the major product. Factors such as sterics, resonance, and charge distribution can also influence the product distribution. It is important to carefully analyze the reaction mechanism and consider all possible products.

4. What are some common mistakes to avoid when solving alkene reaction problems for a chemistry exam?

Some common mistakes to avoid when solving alkene reaction problems for a chemistry exam include:

  • Not balancing the chemical equation properly
  • Incorrectly identifying the type of reaction
  • Not considering stereochemistry or regiochemistry effects
  • Forgetting to include the correct reagents or their roles in the reaction
  • Not considering all possible products and only predicting the major product
  • Not understanding the reaction mechanism and applying the wrong steps

5. Are there any helpful tips for solving alkene reaction problems for a chemistry exam?

Yes, here are a few tips that can help when solving alkene reaction problems for a chemistry exam:

  • Practice drawing reaction mechanisms and identifying the roles of reagents
  • Understand the general properties of reagents and how they influence the reaction
  • Pay attention to the reaction conditions and any specific instructions given
  • Draw out the intermediate steps and consider the stability of each intermediate and transition state
  • Double check your work and make sure you have considered all possible products
  • Review the different types of reactions and their mechanisms beforehand

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