Hydrocarbons: Properties, Reactions, and Isomerism

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Questions and Answers

Which of the following statements accurately describes the composition of hydrocarbons?

  • They consist only of carbon, hydrogen, and oxygen.
  • They consist of carbon and nitrogen only.
  • They consist of carbon, hydrogen, and nitrogen.
  • They consist of carbon and hydrogen only. (correct)

Which of the following is an example of a saturated hydrocarbon?

  • Ethene
  • Benzene
  • Methane (correct)
  • Acetylene

What structural feature differentiates alkanes from alkenes and alkynes?

  • Alkanes are cyclic; alkenes and alkynes are linear.
  • Alkanes have only carbon-carbon single bonds; alkenes and alkynes contain multiple bonds. (correct)
  • Alkanes have carbon-carbon triple bonds; alkenes have double bonds.
  • Alkanes have carbon-carbon double bonds; alkenes and alkynes have single bonds.

What is the process of converting ethene to ethane called?

<p>Hydrogenation (A)</p> Signup and view all the answers

Which feature is characteristic of aromatic hydrocarbons?

<p>They possess a cyclic structure with delocalized π electrons. (A)</p> Signup and view all the answers

What is the term for isomers that differ in the arrangement of atoms due to the restricted rotation around a double bond?

<p>Geometric isomers (D)</p> Signup and view all the answers

Which statement explains why alkanes with branched chains tend to have lower boiling points than their straight-chain isomers?

<p>Branched alkanes have a smaller surface area for van der Waals interactions. (C)</p> Signup and view all the answers

What is the primary reason for using compressed natural gas (CNG) in automobiles?

<p>It causes less pollution than petrol. (B)</p> Signup and view all the answers

Which of the following reactions is characteristic of alkenes due to the presence of the pi bond?

<p>Addition (D)</p> Signup and view all the answers

What is the process of heating higher alkanes to produce smaller alkanes and alkenes called?

<p>Cracking (B)</p> Signup and view all the answers

Which type of reaction do alkanes typically undergo when exposed to halogens under ultraviolet light?

<p>Substitution (B)</p> Signup and view all the answers

In the context of electrophilic aromatic substitution, what is the role of a Lewis acid catalyst, such as AlCl3?

<p>To generate the electrophile. (A)</p> Signup and view all the answers

Which of the following is a possible product of incomplete combustion of hydrocarbons?

<p>Carbon monoxide (C)</p> Signup and view all the answers

What is the effect of a meta-directing group on an aromatic ring during electrophilic substitution?

<p>It directs the incoming group to the meta position. (C)</p> Signup and view all the answers

Which of the following best describes the term 'conformations' in the context of alkanes?

<p>Different spatial arrangements of atoms resulting from rotation around C-C single bonds. (A)</p> Signup and view all the answers

What property makes benzene resistant to addition reactions under normal conditions?

<p>The stability gained from the delocalization of π electrons. (A)</p> Signup and view all the answers

Which of the following is an application of alkynes?

<p>In arc welding (D)</p> Signup and view all the answers

What is the primary reason for the toxicity and carcinogenicity associated with certain polynuclear aromatic hydrocarbons?

<p>Their ability to intercalate into DNA and disrupt replication. (C)</p> Signup and view all the answers

What is the purpose of using soda lime in the decarboxylation of carboxylic acids to form alkanes?

<p>Soda lime facilitates the removal of carbon dioxide. (B)</p> Signup and view all the answers

What is the relationship between the stability and energy of staggered conformation?

<p>Staggered conformations have lower energy and are more stable. (C)</p> Signup and view all the answers

What major factor accounts for the difference in physical properties?

<p>Difference is structures gives different points and properties. (B)</p> Signup and view all the answers

What is the difference between Alkyl group or substituents?

<p>Alkyl group have a hydrogen atom removed from alkanes. (A)</p> Signup and view all the answers

If given an IUPAC name for a certain structure how would one write the structure?

<p>Write the longest chain then add other atoms, then add number of hydrogen atoms. (C)</p> Signup and view all the answers

What do you produce through the following reaction CH-C1+H2 ->

<p>Alkane+HC1 (C)</p> Signup and view all the answers

What is the main cause of increase in boiling point?

<p>Increase in molecular mass (B)</p> Signup and view all the answers

What is the mechanism for halogenation

<p>The three steps are Initiation, Propagation and Termination (C)</p> Signup and view all the answers

How do you produce a halogenated product when an alkane attacks a methane molecules?

<p>Methyl free radical is obtained and attacked with second chlorine. (B)</p> Signup and view all the answers

What do you form when alkanes are heater in the presence of dioxygen(air)

<p>Completely oxidized forms of carbon dixoide and water with large of heat. (D)</p> Signup and view all the answers

What reagents are needed for n-Alkanes to heat to isomerise to branch chained?

<p>anhydrous aluminium chloride and hydrogen chloride gas (C)</p> Signup and view all the answers

How are alkynes named differently than alkanes?

<p>with yne ending vs ane . (D)</p> Signup and view all the answers

Alkynes are named as derivatives of what compound?

<p>Acetylene (C)</p> Signup and view all the answers

Describe the orbital overlapping around ethyne

<p>consist of one σ bond, two C-H σ bonds,and two C-C π bonds (D)</p> Signup and view all the answers

How does one prepare ethyne on an industrial scale?

<p>treating calcium carbide with water (C)</p> Signup and view all the answers

Select the correct trend for acidic behavior?

<p>Alkynes&gt;allkenes&gt;alkanes (D)</p> Signup and view all the answers

Majority of the alkynes are a form for what type of addition reactions?

<p>electrophilic (C)</p> Signup and view all the answers

What is the most important use of the product formed by combining molecules of ethene at high temperature and pressure and in te presence of a catalyst?

<p>Create polythene sheets and bags (A)</p> Signup and view all the answers

Arenes are known as...

<p>Possesing a pleasent odor/smell. (A)</p> Signup and view all the answers

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Flashcards

What are hydrocarbons?

Compounds containing only carbon and hydrogen.

What is LPG?

Liquified petroleum gas, a common fuel source.

What is CNG?

Compressed natural gas, a fuel alternative to gasoline.

What are alkanes?

Saturated hydrocarbons with single C-C bonds.

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What is the general formula for alkanes?

Open chain alkanes with the formula CnH2n+2.

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What are structural isomers?

Same molecular formula but different structural arrangements.

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What are chain isomers?

Isomers differing in carbon chain arrangement.

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What is a primary carbon?

A carbon bonded to only one other carbon.

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What are alkyl groups?

Alkyl groups are substituents derived from alkanes.

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What is hydrogenation?

Adding hydrogen to unsaturated compounds to form alkanes.

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What catalysts can be used for hydrogenation?

Using Pt, Pd, or Ni catalysts for hydrogenation reactions.

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What is the Wurtz reaction?

Reaction of alkyl halides with Na to form higher alkanes.

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What is decarboxylation?

Removing COâ‚‚ from carboxylic acids to form alkanes.

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What is Kolbe's electrolytic method?

Electrolysis of a carboxylic acid salt, forming an alkane.

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What are van der Waals forces?

Weak intermolecular forces in alkanes.

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What is halogenation?

Replacing H atoms with halogens.

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What are conformations?

Spatial arrangements from rotation around C-C single bonds.

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What is torsional strain?

Repulsive interaction affecting conformational stability.

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What is a staggered conformation?

Conformation with atoms as far apart as possible.

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What are alkenes?

Unsaturated hydrocarbons with at least one double bond.

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What are geometrical isomers?

Isomers with same structure but different spatial arrangement.

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What is hydrohalogenation?

Adding a halogen acid to an alkene.

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What is Markovnikov's rule?

The negative part adds to the carbon with fewer hydrogens

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What is Kharasch effect?

Hydrogen halides with ROOR yields anti-Markovnikov addition. This is peroxide effect.

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What happens during ozonolysis?

Alkenes react with ozone to form ozonide.

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What is polymerization?

Combining many small units to form a large molecule.

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What are alkynes?

Unsaturated hydrocarbons with at least one triple bond.

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How is and alkyne formed

The reaction called dehydrohalogenation forms an alkyne.

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How can alkynes, alkenes and alkanes can be told apart

Used to identify alkynes, alkenes and alkanes.

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What is benzene?

A small molecule formed by joining 3 ethyne molecules. Precursor for many organic compounds.

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What is ethene?

Has two carbon atoms. Reacts with halogens to form ethyl halide.

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What makes benzene special

Has the special property called Aromaticity.

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Reactions of hydrocarbons with arenes characterised

The reactions of the compounds follow a specific trend.

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What is carcinogenicity

Carcinogens damage the cells and result in adverse effects on health/

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Study Notes

  • Hydrocarbons are compounds containing carbon and hydrogen.
  • Primarily sourced from coal and petroleum, hydrocarbons serve as major energy sources.
  • They are also used as petrochemicals for commercially important products.
  • Liquefied petroleum gas (LPG) and compressed natural gas (CNG) are derived from petroleum.
  • Hydrocarbons classification includes:
    • Open chain
    • Saturated (alkanes)
    • Unsaturated (alkenes and alkynes)
    • Cyclic (alicyclic)
    • Aromatic compounds

Alkane Reactions

  • Free radical substitution
  • Combustion
  • Oxidation
  • Aromatization

Alkene and Alkyne Reactions

  • Undergo addition reactions that are mainly electrophilic.

Aromatic Hydrocarbon Reactions

  • Undergo electrophilic substitution, and addition only under particular conditions

Isomerism

  • Alkanes have conformational isomerism with staggered conformations more stable.
  • Alkenes have geometric isomerism due to restricted double bond rotation.
  • Benzene and its compounds show characteristics of aromaticity.
  • Aromaticity is determined by specific electronic structure meeting Hückel's rule.
  • Substituents on benzene affect the ring's reactivity and direct incoming groups.
  • Polynuclear hydrocarbons can be carcinogenic.

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