HYDROCARBONS - in 1 Shot || FULL Chapter Coverage (Concepts+PYQs) || Class 11th ORGANIC CHEMISTRY
NCERT Wallah・2 minutes read
The class revises hydrocarbons, focusing on alkanes, alkenes, alkynes, and aromatic hydrocarbons, with alkanes being referred to as saturated hydrocarbons with low reactivity and structural isomerism. Conformational isomerism in alkanes involves different conformers, with staggered confirmations being more stable than eclipsed, and various methods can convert alkanes, alkenes, and alkynes into other hydrocarbons through addition or reduction reactions.
Insights
- Alkanes are saturated hydrocarbons with low reactivity, known as paraffins, and can exhibit structural isomerism based on chain length and branching positions.
- Conformational isomerism in alkanes involves free rotation around single bonds, leading to different conformers like the eclipse and staggered confirmations.
- Various methods can convert alkanes, including catalytic hydrogen addition and reactions like the Sachar Sender reaction, Woods reaction, Franklin reaction, and Soda Lime D carbosynth reaction.
- Alkenes, unsaturated hydrocarbons with restricted rotation due to double bonds, exhibit geometric isomerism, and can be prepared from alkynes through methods like partial reduction, halogenation, and dehydration of alcohols.
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Recent questions
What are the general properties of alkanes?
Alkanes are saturated hydrocarbons with low reactivity.
How are alkenes different from alkanes?
Alkenes have double bonds and restricted rotation.
How can alkanes be converted into alkenes?
Alkanes can be converted by removing hydrogen.
What is the significance of geometric isomerism in alkenes?
Geometric isomerism in alkenes affects their properties.
How are alkynes different from alkenes and alkanes?
Alkynes contain triple bonds and exhibit unique reactions.
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Summary
00:00
Understanding Alkanes: Isomerism and Conformers
- The class is focused on revising the chapter on Hydrocarbons, specifically alkane, alkene, alkyne, and aromatic hydrocarbons.
- Alkanes fall under the category of saturated hydrocarbons with the general formula represented as CnH2n + 2.
- Alkanes are also known as paraffins due to their low chemical reactivity.
- Alkanes can exhibit structural isomerism, showing differences in chain length and branching positions.
- Five structural isomers of C6H14 can be found, including n-hexane, 2-methylpentane, 3-methylpentane, 2,3-dimethylbutane, and 2,2-dimethylbutane.
- Conformational isomerism in alkanes involves free rotation around carbon-carbon single bonds, leading to different conformers.
- Conformational isomers, or conformers, are non-separable and rapidly interconvertible due to free rotation.
- Extreme cases of conformers include the eclipse confirmation, where hydrogen atoms are as close as possible, and the staggered confirmation.
- The Newman projection is used to visualize conformers, with the front carbon showing three hydrogens and the back carbon also having three hydrogens.
- Conformational isomers of alkanes can be represented in Newman projections, showcasing the arrangement of hydrogen atoms on carbon atoms.
17:51
Butane Conformations: Stability and Isomer Formation
- Eclipse confirmation is confirmed due to the proximity of hydrogen atoms in the New Man Projection.
- Staggered version involves hydrogen atoms being as far apart as possible.
- Staggered confirmation is more stable than Eclipse due to less torsional strain and repulsion.
- The process involves rotating carbon atoms and hydrogen groups to achieve different confirmations.
- The staggered confirmation is the most stable, followed by the partially eclipsed, and then the fully eclipsed.
- The conformational isomers of butane are created through rotations of 60 degrees.
- The stability of the confirmations is determined by the proximity of groups and the level of repulsion.
- The energy levels of the confirmations are inversely related to their stability.
- Structural isomers are formed based on the confirmations achieved through rotations.
- The stability of confirmations is influenced by the distance between groups, affecting repulsion and torsional strain.
37:06
Methods of Converting Alkanes and Alkynes
- Alkanes can be converted through various methods, with the first method involving the addition of hydrogen in the presence of catalysts like nickel, palladium, or platinum at room temperature.
- The catalytic hydrogen addition breaks the pi bond in alkene or alkyne, forming two new sigma bonds on each carbon.
- The reaction, known as Sachar Sender reaction, is termed so when catalytic hydrogen addition is done using nickel as the catalyst.
- Alkynes can also be converted through the addition of hydrogen twice, resulting in complete saturation.
- The second method involves the reduction of alkyne halides using zinc and acetic acid, with reactivity order being highest for alkynes and lowest for alkyl fluorides.
- The Woods reaction, involving two moles of alkyne and sodium metal in dry ether, is ideal for forming symmetrical alkanes.
- The Franklin reaction, similar to the Woods reaction, uses zinc and sodium metal in dry ether to produce alkanes by combining with RR and zinc halogen.
- The third method, known as the Soda Lime D carbosynth reaction, involves heating sodium salt of carboxylic acid with soda lime to produce alkane.
- The fourth method utilizes carbonyl compounds, undergoing reduction in the presence of zinc amalgam and concentrated acetic acid to convert into hydrocarbons.
- Another method involves the use of Grignard reagent, formed by reacting magnesium with dry ether, to convert into alkanes through the addition of water and acidic hydrogen.
58:36
Chemistry of Alkanes and Reactions Summary
- Alcohol contains acidic hydrogen and oxygen with a negative charge.
- Ammonia steals acidic hydrogen and forms alkane.
- Alkanes are non-polar and insoluble in water.
- Alkanes are soluble in organic solvents like benzene.
- Branching in isomeric alkanes affects their boiling point.
- Alkanes exist as gases, liquids, and solids based on their mass.
- Halogenation involves substitution reactions with different reactivity orders.
- Controlled oxidation of alkanes can produce different products under varied conditions.
- Isomerization converts one isomer into another, altering the structure.
- Reaction of alkanes with steam produces a mixture of carbon monoxide and hydrogen, known as synthesis gas.
01:19:54
"Creating Alkenes from Alkanes through Pyrosis"
- Pyrosis is used to create new hydrocarbons by breaking down c6 a1.
- Different types of hydrocarbons can be obtained through this process.
- Alkenes can be formed by removing hydrogen from alkane molecules.
- Small alkanes can be converted into small alkenes through heat-induced breakdown.
- Alkenes are crucial in the category of unsaturated hydrocarbons.
- The general formula for alkenes is cnh2n, starting with a minimum of two carbons.
- Alkenes have restricted rotation due to the double bond, leading to geometric isomerism.
- Geometric isomerism in alkenes requires different terminal valencies on the carbons.
- Cis-trans isomerism is determined by the arrangement of groups on the same or opposite sides of the double bond.
- The SIP rule prioritizes groups based on atomic numbers to determine cis-trans isomerism in alkenes.
01:39:58
Methods of Alkene Preparation and Reactions
- Preparation of alkene from alkyne involves different methods.
- The first method is partial reduction of alkyne using H2 with a catalyst like Lind Lars.
- The catalyst is crucial to stop the reaction at the right time to convert alkene into alkane.
- The second method involves the reaction of halide alkyne with halogen to form more stable alkene.
- The major product is determined by the Set Jaffa rule, favoring more substituted alkenes.
- The third method uses vicinal dihalide to form alkene through elimination reactions.
- Dehydration of alcohol with concentrated sulfuric acid leads to the formation of alkene.
- Physical properties of alkenes include insolubility in water and higher boiling points with increased mass.
- Addition reactions to alkenes involve breaking the double bond with reactions like H2 addition.
- Marconic and Anti-Marconic rules determine the addition of different substances to alkenes.
- Oxidation reactions with substances like N Bromo Saxon Maide and KMnO4 lead to the formation of carboxylic acids from alkenes.
02:01:24
Ozone lysis forms aldehydes and ketones efficiently.
- Ozone lysis is a crucial reaction to form aldehydes and ketones from carbonyl compounds.
- The process involves adding ozone first, followed by ozonide formation and subsequent conversion to aldehydes or ketones.
- Alkenes play a significant role in this reaction, with the double bond being crucial for the transformation.
- Ethanol can be converted to acetaldehyde through a double bond break, showcasing the versatility of the reaction.
- Polymerization of alkenes is a practical application, where monomers are transformed into polymers under specific conditions.
- Polyethylene, commonly known as polythene, is a prominent example of a polymer derived from alkenes.
- Alkynes, a distinct class of hydrocarbons, exhibit unique properties and reactions compared to alkenes.
- The preparation of alkynes involves methods like calcium carbide hydrolysis and vicinal dihalide reactions.
- Alkynes can be distinguished through tests like the Tollens test, which reveals the presence of acidic hydrogen in the compound.
- Addition reactions on alkynes, such as hydrogenation and halogenation, lead to the formation of alkenes or alkanes based on the reaction conditions.
02:21:26
Alkynes, Benzene, and Electrophilic Substitution Reactions
- Alkynes undergo ozone lysis, forming ozonide.
- Ozonide formation involves breaking both bonds in alkynes.
- Polymerization in alkynes can be linear or cyclic.
- Linear polymerization in alkynes involves high temperature, pressure, and catalyst.
- Alkynes can undergo geminal dihalogenation.
- Aromatic hydrocarbons like benzene can be prepared through cyclic polymerization of ethyne.
- Benzene follows Huckle's rule of aromaticity.
- Benzene's resonance hybrid structure involves sp2 hybridization.
- Benzene undergoes electrophilic substitution reactions due to its electron-rich nature.
- Electrophilic substitution of benzene with nitric acid and sulfuric acid generates electrophile NO2, leading to nitrobenzene formation.
02:40:33
Lewis Acid Catalysts in Organic Chemistry
- AlCl3 or Br2 in the presence of FeBr3 acts as both a Lewis acid and a catalyst, generating an electrophile.
- When Cl2 is heated, homolytic fusion occurs, leading to radical generation and the need for an electron-deficient species like AlCl3 to generate an SP.
- Chlorination of Chlorobenzene occurs with Cl2 in FeBr3, while bromination results in Bromobenzene.
- Sulfonation of Benzene with fuming acid and N-hydrous AlCl3 generates a neutral electrophile, SO3, leading to the formation of Benzene Sulfonic Acid.
