Alkenes and Dienes – problem list
The addition of hydrogen to 1-methylcyclohexene leads to the formation of a single product, in the presence of palladium on carbon. Justify the result.
What will be the major product obtained on addition of HBr over 2-methylbut-1-ene?
Compare the result of the reaction of bromine in CCl4 with the E and Z isomers of but-2-ene.
Addition of borane in THF followed by hydrogen peroxide in basic medium of 1-methylcyclohexene leads to the formation of a mixture of enantiomers. Draw their structures.
Justify the order of reactivity of the following alkenes against acid catalyzed hydration reactions:
Complete the following scheme:
Write the fitted equations to perform the following transformations:
- a) propene → 1-bromopropane.
- b) propene → 2-chloropropane
- c) propene → propan-1,2-diol
- d) propene → propane-2-ol
- e) but-2-ene → acetic acid
- f) styrene → benzaldehyde
Complete the scheme (A-F), identifying the following species (radical initiator, reductant, electrophile, nucleophile, and oxidant) for the reactions described. Also, indicate whether the process follows Markovnikov’s rule and whether the stereoselectivity is syn or anti.
Choose the starting olefin (I-III) to prepare each of the compounds (A-F) and describe the reagents and reaction conditions you consider necessary for each case.
Indicate in a reasoned way if the following statements are true or false:
- a) The addition of hydrogen halides to alkenes always gives the Markovnikov addition product.
- b) Ozonolysis of an alkene produces two carbonyl compounds.
- c) Acid-catalyzed hydration of alkenes has syn stereochemistry.
- d) The addition of halogens to alkenes and the formation of halohydrins are anti additions.
Draw the major product (A-F) obtained in each of the following reactions (a-f):
Justify the following result by considering the reaction mechanism:
Complete the following scheme:
What products would be obtained in the ozonolysis of the following alkenes?
Draw the structures of the 1,2 and 1,4 addition products of the following dienes with Br2 and H3O+.
Predict the major product obtained in the Diels-Alder reaction of the following dienes with the dienophiles given.
Using as starting product any of the olefins (I-III),
describe the procedures to obtain:
- a) a primary haloalkane
- b) a secondary haloalkane
- c) a cyclic ketone
- d) a dialdehyde
- e) a haloalkene
- f) cyclopentane
- g) propanedioic acid
Describe the reagents needed to perform the following transformations:
Describe the process of formation of a trimer from 2-methylpropene by treatment with BF3 and traces of water in methylene chloride at low temperature.
Justify the experimental results (relative rate of epoxidation of alkenes) described in the following table:
The following reagents (indicated in the table) are used for various reactions on alkenes. Identify in which reactions they participate and which one acts as an electrophile, nucleophile, oxidant or reductant.
|HBr / peroxides|
Draw the structure of the product(s) obtained from cyclopentene with the following reagents, taking into account the stereochemistry of the process:
- a) 1) H2SO4; 2) H2O
- b) CHCl3 / t-BuOK
- c) HBr / peroxides
- d) HBr
- e) Br2
- f) Cl2 / H2O
- g) H2O / H3PO4
- h) R-COOOH
Complete the following reaction:
Describe the stereochemistry of the product/s obtained on the addition of chlorine to (E)-hex-3-ene.
Choose the appropriate starting product (I or II), to obtain the following compounds (A-D).
Relate the following concepts (a-d) to the reactions (I-IV) described below:
- a) Markovnikov addition I) mercuriation / demercuriation
- b) stereospecific process II) hydration of alcohols
- c) anti addition III) catalytic hydrogenation
- d) anti-Markovnikov addition IV) hydroboration / oxidation
State the products of bromine addition on cyclopentene and methylcyclohexane, paying special attention to stereochemistry.
Describe the stereoisomers obtained in the reaction of formation of halohydrins with a mixture of (E)- and (Z)-pent-2-ene.
Draw the structures of the products obtained from the reaction with diazomethane of:
- a) cycloheptene
- b) 1-methylcyclohexene
- c) (E)-but-2-ene
Describe the products obtained by treatment with a peracid of:
- a) 1,2-dimethylcyclohexene
- b) 2-methylbut-2-ene
- c) 2-methylpropene
- d) cyclohexa-1,4-diene
The Z– and E-isomers of hex-2-ene react independently by:
- a) catalytic hydrogenation
- b) electrophilic addition of HBr
- c) epoxidation
- d) ozonolysis
Deduce which reactions give the same compound from both isomers.
Draw and clearly indicate the stereochemistry of the compounds obtained from the addition of 1 mol of bromine on alkenes I-IV.
The oxidative cleavage with permanganate in basic medium, followed by treatment with an acid, of a series of alkenes leads to the formation of the following fragments (a-f). Identify what would be the starting products for each of the cases.
Determine the structure of a hydrocarbon of molecular formula C8H14 which gives by catalytic hydrogenation a compound of molecular formula C8H18. Ozonolysis of said compound leads to the formation of acetaldehyde, acetone and propanedial. Draw the three possible constitutional isomers obtained when said hydrocarbon is treated with 1 mol of HCl.
Draw the structure of the dimers resulting from the treatment of the following alkenes with a mineral acid.
The following compounds (a-f) come from the ozone reaction of alkenes followed by treatment with a reductant such as Me2S.
Choose the appropriate alkene(s) from the following (I-VIII) for obtaining these compounds (a-f).
Represent the products resulting from the treatment with OsO4 of the following alkenes (I-VI):
Identify the conjugate systems of the following molecules (a-e), determining which would be suitable for the Diels-Alder reaction:
Predict the product(s) (A-F) of the Diels-Alder reactions described below:
Draw the structure of the 4 major products obtained in the radical polymerization of isoprene.
Indicate the product(s) obtained when buta-1,3-diene is treated with:
- a) 1 mol Br2
- b) 1 mol HBr (-15 ºC)
- c) 1 mol HBr (45 ºC)
- d) propinoic acid
- e) H2 / Pd(C)
Complete the following scheme:
Draw the structure of the hydrogenation products of 1,2-dimethylcyclohexene, (E)-but-2-ene and (Z)-but-2-ene.
State the product(s) obtained on the addition of bromine in CCl4 to cyclohexene.
The addition of chlorine in the presence of water on 1-methylcyclohexene gives rise to a pair of products which are enantiomers of each other. What would be their structures?
Treatment of 3-ethyl-pent-2-ene with sulfuric acid in water leads to the formation of an alcohol. Deduce reasoned the structure of the product obtained.
Describe the reactions and products obtained from cyclohexene and (E)-but-2-ene when they react independently with a) diazomethane and with b) peracetic acid.
Justify the following result:
Choose the appropriate dienes and dienophiles for obtaining the following adducts (a-j):
Point out, in the following structures (a-c), which fragment acts as a diene and as a dienophile, and predict the carbon skeleton (disregarding stereochemistry) that would be obtained by an intramolecular Diels-Alder reaction.
Justify the low reactivity of (Z,Z)-hexa-2,4-diene in the Diels-Alder reaction.