Alkene + KMnO4 Reaction
TLDRThe script discusses the chemical reactions of cyclohexene with potassium permanganate (KMnO4) under various conditions. It explains the formation of a diol with syn stereochemistry under basic and cold conditions, and the oxidation to carboxylic acids under acidic and heated conditions. The script also covers the reaction mechanisms, including manganate ester formation and hydrolysis, and the use of osmium tetroxide as an alternative reagent. Furthermore, it explores stereoisomerism, distinguishing between constitutional, enantiomers, and diastereomers, particularly focusing on the diastereomeric relationship in the presence of a methyl group.
Takeaways
- 🌟 Cyclohexene reacts with potassium permanganate (KMnO4) under basic conditions to undergo syn dihydroxylation, resulting in a cis-1,2-diol with identical products due to internal symmetry.
- 🔍 The reaction mechanism involves the formation of a manganate ester intermediate, which then hydrolyzes to form the cis-1,2-diol.
- 🌐 OsO4 followed by sodium bisulfite can achieve the same cis-1,2-diol product, indicating an alternative pathway to the same outcome.
- 🔄 When a cyclohexene ring with a methyl group reacts with KMnO4 under cold basic conditions, two different stereoisomers are formed, which are diastereomers, not enantiomers.
- 📚 Constitutional isomers differ in connectivity, while stereoisomers differ in spatial arrangement despite the same connectivity.
- ⚗️ The reaction of cis-2-butene with potassium permanganate under acidic conditions and heat leads to the cleavage of the carbon-carbon bond and the formation of carboxylic acids.
- 🔥 Primary carbon atoms in the cleaved bond are fully oxidized to carboxylic acids, while secondary carbon atoms form ketones, and methyl groups are oxidized to CO2.
- 📉 The presence of a double bond in the molecule dictates the addition of an oxygen atom to form the final products after bond cleavage.
- 📚 Peracetic acid can convert 1,2-diols into aldehydes and ketones, with the specific product depending on the position and type of hydroxyl groups in the diol.
- 🌡 The reaction conditions, such as temperature and pH, significantly influence the type of products formed in reactions with potassium permanganate.
- 🧪 Understanding the stereochemistry and the reactivity of different functional groups is crucial for predicting the outcomes of organic reactions.
Q & A
What is the major product when cyclohexene reacts with potassium permanganate (KMnO4) under basic conditions at low temperature?
-The major product is a 1,2-diol with syn addition, meaning the two hydroxyl groups will be on the same side.
Why are the two products of cyclohexene with KMnO4 considered identical?
-The two products are considered identical because they are meso compounds, which have an internal plane of symmetry.
Which other reagent can produce the same product as KMnO4 in the dihydroxylation of cyclohexene?
-Osmium tetroxide (OsO4) followed by sodium bisulfite (NaHSO3) can also produce the same cis-1,2-diol product.
What intermediate is formed when cyclohexene reacts with KMnO4 under basic conditions?
-A manganate ester intermediate is formed.
Describe the mechanism of dihydroxylation with osmium tetroxide (OsO4).
-The double bond in cyclohexene breaks and forms a bond with the osmium tetroxide, creating an osmate ester, which is then hydrolyzed with sodium bisulfite to produce the cis-1,2-diol.
What happens when a 1,2-diol reacts with periodic acid (HIO4)?
-The carbon-carbon bond in the 1,2-diol cleaves, and the diol is oxidized to form aldehydes.
How many products are formed when methyl-substituted cyclohexene reacts with KMnO4 under cold basic conditions?
-Two different stereoisomers are formed, as the product no longer has an internal plane of symmetry, leading to diastereomers.
What type of isomers are formed from the methyl-substituted cyclohexene reaction with KMnO4?
-Diastereomers are formed because not all chiral centers change, distinguishing them from enantiomers.
What is the product when cis-2-butene reacts with KMnO4 under cold basic conditions?
-A meso compound is formed, specifically a 1,2-diol with syn addition.
What is the result of reacting an alkene with concentrated KMnO4 under acidic conditions and heat?
-The carbon-carbon bond cleaves, and depending on the substitution, primary carbons are oxidized to carboxylic acids, secondary carbons to ketones, and methyl groups to CO2.
Outlines
🧪 Syn-Dihydroxylation of Cyclohexene with KMnO4
This paragraph explains the chemical reaction of cyclohexene with potassium permanganate (KMnO4) under basic conditions at low temperatures, resulting in syn-dihydroxylation. The reaction yields a diol with syn stereochemistry, where two hydroxyl groups are added to the same side of the molecule. Due to the molecule's internal plane of symmetry, the two possible products are identical, leading to a single product outcome. The paragraph also discusses an alternative method using osmium tetroxide (OsO4) followed by sodium bisulfite to achieve the same cis-1,2-diol product. The reaction mechanism for the formation of a manganate ester intermediate is outlined, which is then hydrolyzed to form the diol.
🔍 Stereoisomerism in Cyclohexene Derivatives
The second paragraph delves into the stereochemistry of cyclohexene derivatives, specifically when a methyl group is present. The reaction of such a compound with potassium permanganate under cold basic conditions leads to the formation of two different stereoisomers due to the lack of an internal plane of symmetry. These isomers are identified as diastereomers, not enantiomers, as not all chiral centers undergo a change in configuration. The paragraph further explores the oxidation of 1,2-diols to aldehydes and ketones using periodic acid (HIO4), emphasizing the distinction between aldehyde and ketone formation based on the carbon's position in the molecule.
🔥 Oxidative Cleavage of Alkenes with KMnO4
The final paragraph discusses the oxidative cleavage of alkenes, exemplified by cis-2-butene, when reacted with potassium permanganate under acidic conditions and heat. This reaction results in the breaking of the carbon-carbon double bond and the oxidation of the resulting fragments to carboxylic acids or carbon dioxide, depending on their primary or secondary carbon status. The paragraph provides examples to illustrate the oxidation process, highlighting the differences in product formation based on the reaction conditions and the structure of the alkene.
Mindmap
Keywords
💡Cyclohexene
💡Potassium Permanganate (KMnO4)
💡Syn Dihydroxylation
💡Cis-1,2-Diol
💡Manganate Ester
💡Osmium Tetroxide (OsO4)
💡Periactic Acid
💡Diastereomers
💡Enantiomers
💡Constitutional Isomers
💡Meso Compound
Highlights
Cyclohexene reacts with potassium permanganate (KMnO4) under basic conditions to undergo syn dihydroxylation, resulting in a cis-1,2-diol with syn stereochemistry.
The cis-1,2-diol product from cyclohexene and KMnO4 has an internal plane of symmetry, making the two possible products identical and thus yielding only one product.
Osmium tetroxide (OsO4) followed by sodium bisulfite can also achieve the same cis-1,2-diol product from cyclohexene.
An intermediate manganate ester is formed during the reaction of cyclohexene with KMnO4, which later hydrolyzes to the cis-1,2-diol.
Reaction mechanism for the formation of manganate ester from cyclohexene and permanganate ion is detailed, including electron transfer and bond rearrangement.
Osmate ester formation from osmium tetroxide and cyclohexene is similar to the formation of the manganese ester, with a lone pair adjustment.
Reaction of 1,2-diol with periodic acid results in the cleavage of the carbon-carbon bond and oxidation to aldehydes.
The presence of a methyl group in the cyclohexene ring affects the stereochemistry of the resulting diol, leading to two different stereoisomers.
The two stereoisomers from the reaction of cyclohexene with a methyl group and KMnO4 are diastereomers, not enantiomers, due to the change in some but not all chiral centers.
Cis-2-butane reacts with KMnO4 under acidic conditions and heat to cleave the carbon-carbon bond, leading to the formation of carboxylic acids and CO2.
The oxidation level of the cleaved carbon atoms determines whether they form carboxylic acids, ketones, or are fully oxidized to CO2.
Examples are provided to illustrate the oxidation products from the reaction of different structures with KMnO4 under acidic conditions.
Concentrated KMnO4 or the addition of heat during the reaction with cis-2-butane leads to further oxidation beyond the formation of diols.
The reaction conditions, such as temperature and pH, significantly influence the products formed from the reaction of alkenes with KMnO4.
The concept of meso compounds is explained, where internal symmetry leads to a single product from what could be two stereoisomers.
Stereochemistry plays a crucial role in the products formed from the reactions of alkenes with oxidizing agents like KMnO4.
The importance of understanding the connectivity and spatial arrangement of substituents in determining stereoisomer types is highlighted.
Diastereomers are differentiated from enantiomers based on the change in chiral centers during the reaction process.
Transcripts
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