Organic Chemistry: Benzene Compounds
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Questions and Answers

What is the C-C-C bond angle in the benzene ring?

  • 120˚ (correct)
  • 180˚
  • 360˚
  • 90˚

All aromatic compounds produce a fragrant aroma.

False (B)

What hybridization do the carbon atoms in benzene exhibit?

sp2

Each carbon atom in benzene is attached to ___ hydrogen atoms.

<p>1</p> Signup and view all the answers

Match the following components of benzene with their descriptions:

<p>C atom = Attached to 1 H atom and 2 other C atoms Unhybridized p orbital = Forms a circular π bond Bond angle = 120˚ Hybridization = sp2</p> Signup and view all the answers

Which formula type shows all atoms present along with their positions?

<p>Basic Structural Formula (A)</p> Signup and view all the answers

The Skeletal Formula displays all carbon atoms and their positions.

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

What do straight lines in a Detailed Structural Formula signify?

<p>Atoms and bonds that are in the same plane.</p> Signup and view all the answers

In a Detailed Structural Formula, dashed lines indicate atoms and bonds that go into the ______.

<p>page</p> Signup and view all the answers

Match the following types of formulas with their descriptions:

<p>Condensed Formula = Not showing any carbon atoms Skeletal Formula = Shows only functional groups Display Formula = Shows all atoms and their bonds Detailed Structural Formula = Shows atoms in the same plane, behind and out of the page</p> Signup and view all the answers

What type of lines are used to show atoms and bonds that come out of the page?

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

The Basic Structural Formula only shows functional groups.

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

What type of reagent is HBr classified as?

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

A nucleophile is a substance that donates an electron pair.

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

What is the purpose of using an asterisk (*) in the structural formula of enantiomers?

<p>To indicate the chiral carbon.</p> Signup and view all the answers

Cl2 is an example of an _____ reagent.

<p>electrophile</p> Signup and view all the answers

Match the following organic reagents with their classifications:

<p>H+ = Cation CN− = Anion NH3 = Neutral molecule with a lone pair OH− = Base</p> Signup and view all the answers

Which of the following is NOT considered a Lewis acid?

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

Radicals are neutral molecules that cannot be polarized.

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

What is the primary product formed when an alkene reacts with aqueous bromine?

<p>2-bromoethanol (B)</p> Signup and view all the answers

What is meant by an electrophile being attracted to electron-rich regions?

<p>Electrophiles seek out areas with excess electrons to accept them.</p> Signup and view all the answers

The color of bromine water remains orange-brown when mixed with an alkene.

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

A reagent that can accept an electron pair is called a ______.

<p>Lewis acid</p> Signup and view all the answers

What type of reaction occurs when an alkene reacts with aqueous halogen?

<p>Halogenation</p> Signup and view all the answers

Which of the following compounds is a chiral molecule?

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

The reaction of a symmetrical alkene with hydrogen halide produces an __________ product.

<p>alkyl halide</p> Signup and view all the answers

Match the following compounds with their respective products:

<p>Ethene + HBr = 2-bromobutane Alkene + Br2 + H2O = 2-bromoethanol Cyclohexene + Cl2 = Dichlorocyclohexane Propene + HBr = 1-bromopropane</p> Signup and view all the answers

What happens to the bromine water when mixed with an alkene?

<p>It becomes colorless. (A)</p> Signup and view all the answers

The minor product formed from the reaction of alkene with aqueous Br2 is 2-bromoethanol.

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

Identify the halogenation reaction product formed when ethene reacts with Br2.

<p>2-bromoethanol</p> Signup and view all the answers

In the addition of hydrogen halide to a symmetrical alkene, the slightly positive __________ in HX interacts with the π bond.

<p>H</p> Signup and view all the answers

During the halogenation of an alkene, which of the following is NOT a possible product?

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

What type of isomers are 2,3-dimethylbut-2-ene and 2-methylpent-2-ene?

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

All E-Z isomers are also cis-trans isomers.

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

What is the prefix used in nomenclature to indicate geometric isomers with higher priority atoms on the same side?

<p>Z</p> Signup and view all the answers

The melting point of cis-but-2-ene is approximately _____ °C.

<p>-106</p> Signup and view all the answers

Match the isomer with its description:

<p>E-1-bromo-2-chloro-2-fluoro-1-iodoethene = Higher priority atoms on opposite sides Z-1-bromo-2-chloro-2-fluoro-1-iodoethene = Higher priority atoms on the same side</p> Signup and view all the answers

Which of the following statements is true regarding but-2-ene?

<p>It can exist as both cis and trans isomers. (C)</p> Signup and view all the answers

Geometric isomers can form from alkenes with at least one double bond and different groups attached.

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

What is the common name for C3H6?

<p>propene</p> Signup and view all the answers

In alkenes, a geometric isomer can arise when there are _____ or more different atoms/groups attached to a C=C bond.

<p>three</p> Signup and view all the answers

Which type of isomerism is indicated by the terms E and Z?

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

Flashcards

Condensed Formula

A simplified way to write molecular structure showing the arrangement of atoms but not all bonds.

Structural Formula

A representation of a molecule showing all the atoms and their connections (bonds) in a specific arrangement.

Skeletal Formula

A simplified version of a structural formula where only the carbon skeleton and functional groups are shown.

Displayed Formula

Draws out the entire structure of a molecule with all atoms and bonds clearly shown, similar to a structural formula.

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Basic Structural Formula

The most simplified way to show the arrangement of atoms in a molecule, focusing on the main skeleton of the molecule.

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What do dashed lines represent in detailed structural formula?

Dashed lines represent bonds that are going into the page, behind the plane of view, away from the observer.

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What do wedged lines represent in detailed structural formula?

Wedged lines represent bonds that are coming out of the page towards the observer, in front of the plane of view.

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Organic Reagents

Substances that cause reactions to happen to organic compounds.

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Electrophile

Reagents that accept an electron pair (Lewis acids). They are attracted to electron-rich regions in organic compounds.

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Nucleophile

Reagents that donate an electron pair (Lewis bases). They are attracted to positively charged regions in organic compounds.

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How do electrophiles work?

Electrophiles are attracted to electron-rich regions in organic compounds, where they can accept an electron pair to form a new bond.

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How do nucleophiles work?

Nucleophiles donate an electron pair to a positively charged or electron-deficient region in an organic compound.

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Example of an Electrophile

HBr is an example of an electrophile because it can accept an electron pair from an organic compound.

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Example of a Nucleophile

OH− is an example of a nucleophile because it can donate an electron pair to an organic compound.

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Radicals

Reagents that have an unpaired valance electron.

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What makes a good nucleophile?

Nucleophiles have a lone pair of electrons (which they can donate) and are often negatively charged.

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Benzene Ring

A six-membered ring of carbon atoms with alternating single and double bonds, forming a cyclic system with six delocalized electrons.

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Aromatic Compounds

Organic compounds containing a benzene ring as a core structure, often with other functional groups attached.

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What is the hybridization of Carbon atoms in Benzene?

The carbon atoms in benzene are sp2 hybridized, which means they form three sigma bonds and have one unhybridized p orbital.

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How do you name aromatic compounds?

Aromatic compounds are named using the IUPAC system, with substituents attached to the benzene ring named and numbered based on their positions.

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What is the significance of delocalized electrons?

The six delocalized electrons in the benzene ring contribute to its exceptional stability and unique chemical properties.

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Alkene Halogenation with Aqueous Br2

When alkenes react with bromine water (Br2 in water), the orange-brown solution becomes colorless, indicating the formation of a halohydrin (alcohol with a halide substituent). The major product is a 2-bromoethanol, with a minor product being 1,2-dibromoethane.

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What is a halohydrin?

A halohydrin is a type of organic molecule that contains both a halogen atom (like bromine) and a hydroxyl group (-OH) attached to adjacent carbon atoms.

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Symmetrical Alkene + HX

Hydrogen halide (HX) readily reacts with symmetrical alkenes (alkenes with identical groups on each side of the double bond) to form alkyl halides, where the halogen atom (X) attaches to one of the carbon atoms originally involved in the double bond.

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Mechanism of HX addition to alkene

The addition of hydrogen halide (HX) to an alkene occurs through a two-step process. Firstly, the slightly positive hydrogen (H+) of HX attracts the electron pair from the alkene's pi bond, leading to the formation of a carbocation intermediate. Secondly, the halide ion (X-) attacks the carbocation, forming a C-X bond and completing the addition reaction.

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Alkene + HX: What is a carbocation?

A carbocation is a positively charged carbon atom with only three bonds, making it an electron deficient species. Carbocations are highly reactive and are formed as intermediates during reactions like the addition of HX to alkenes.

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Why is the reaction between alkene and HX regiospecific?

The addition of HX to an alkene follows a specific pattern, with the hydrogen atom attaching to the carbon with more hydrogen atoms already attached to it. This is known as Markovnikov's rule. The regiospecificity is due to the relative stability of the carbocation intermediates formed during the reaction.

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What are the types of alkene reactions?

Alkene reactions can be classified into two main types: addition reactions and oxidation reactions. Addition reactions involve the breaking of the double bond and the addition of new atoms or groups to the carbon chain. Oxidation reactions involve the loss of electrons and the gain of oxygen atoms.

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What are the features of the skeletal formula?

The skeletal formula represents a molecule by showing only the carbon skeleton and functional groups, omitting carbon and hydrogen atoms that are attached to carbon atoms. It emphasizes the connectivity of atoms and functional groups, simplifying molecular representation for clarity and conciseness.

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Why is the skeletal formula used?

The skeletal formula provides a concise representation of the structure of a molecule, removing visual clutter and highlighting the key bonding relationships. This makes it easier to compare and analyze different molecules, especially when dealing with complex structures.

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How is the skeletal formula different from the displayed formula?

The skeletal formula omits all the hydrogen atoms attached to carbon atoms, whereas the displayed formula shows all atoms and bonds explicitly, making it more detailed but potentially more complex to analyze. The skeletal formula is thus more concise but less detailed.

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Functional Group Isomers

Molecules with the same molecular formula but different functional groups.

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Geometric Isomers

Molecules with the same structural formula but different spatial arrangements due to restricted rotation around a double bond.

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Cis-trans Isomers

A type of geometric isomer where two groups are on the same side of the double bond (cis) or opposite sides (trans).

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E-Z Isomers

A more general way to classify geometric isomers based on the priority of substituents on the double bond, with 'E' for entgegen (opposite) and 'Z' for zusammen (together).

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What makes a good electrophile?

Electrophiles can accept an electron pair and are often positively charged or have an incomplete octet, making them electron deficient.

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What is a carbocation?

A positively charged carbon atom with only three bonds, making it an electron deficient species that is highly reactive.

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Study Notes

Course Information

  • Course title: PRP 1016, Chemistry 1
  • Learning unit 7: Organic Chemistry I
  • Prepared by: Eswaran Madiahlangan

Learning Unit 7.1: Introduction to Organic Chemistry

  • Learning Objectives (7.1):
    • Describe the properties of carbon atoms.
    • Differentiate functional groups and classify homologous series.
    • Represent organic compounds using various chemical formulae.
    • Name organic compounds according to the IUPAC system.

What is Organic Chemistry?

  • The study of organic compounds, which are compounds containing carbon.
  • Includes hydrocarbon compounds and organic compounds.

Properties of Carbon Atom

  • Tetravalent: Carbon forms four covalent bonds via sharing of its valence electrons.
  • Requires four (4) additional electrons to achieve octet configuration electrons.
  • C-C bonds are relatively strong bonds.
  • Catenation - Group 14 Element Properties
  • Average bond enthalpies (kJ/mol): C-C (+347), C=C (+612), C≡C (+838), C-H (+413), C-O (+358), Si-Si (+226), Si-H (+318)
  • Forms diverse compounds due to:
    • Long carbon chains or ring structures
    • Many different groups or elements.

Classifications of Organic Compounds

  • Based on:
    • Arrangement of carbon chains (Aliphatic, Alicyclic, Arene)
    • Presence of double or triple bonds (Saturated, Unsaturated)
    • Functional groups (Homologous series)

Arrangement of Carbon

  • Aliphatic: Open chain arrangement
  • Alicyclic: Consists of closed ring(s) of carbon atoms.
  • Arene: Consist of at least one benzene ring

Presence of Multiple Bond

  • Saturated: Contains only carbon-carbon single bonds.
  • Unsaturated: Contains one or more double or triple carbon-carbon bonds.

Functional Groups & Homologous Series

  • A functional group is an atom or group of atoms responsible for the chemical properties of organic molecules.
  • Organic compounds with the same functional groups belong to the same homologous series.

Functional Groups and Homologous Series

Homologous Series General Formula Functional Group
Alkanes CnH2n+2 Carbon-carbon single bond
Alkenes CnH2n Carbon-carbon double bond
Alkynes CnH2n-2 Carbon-carbon triple bond
Alkyl Halides CnH2n+1X (X is halogen) Halide
Alcohols CnH2n+2O Hydroxyl group
Aldehydes CnH2nO Carbonyl group
Ketones CnH2nO Carbonyl group
Carboxylic Acids CnH2n+1O2 Carboxyl group
Amines Amine group
Amides Amide group
Esters Carboxylate group
Ethers Alkoxy group bonded to carbon
Nitriles Cyano group

Homologous Series

  • Members can be prepared by the same general method.
  • Have the same general formula
  • Members in the same series have a difference of CH2 between successive members.
  • Show an increase of 14 mass units in their RMM from the previous member.
  • Gradual changes in physical properties (e.g., boiling point) with increasing RMM.

Representing Organic Compounds

  • Molecular formula: Shows the number of atoms of each element.
  • Condensed formula: Shows the atoms and how they are connected, but omits bonds.
  • Displayed formula: Shows all atoms and bonds
  • Skeletal formula: Shows the arrangement of the carbon skeleton but omits the carbons and hydrogens to simplify.

Structural Formula

  • Basic Structural Formula: Shows all atoms and bonds.
  • Condensed Formula: Shows all atoms but omits some bonds.
  • Skeletal Formula: Shows the carbon skeleton but not the hydrogen atoms

IUPAC Nomenclature

  • Comprehensive naming system for organic compounds.
  • Provides a unique name for each compound.
  • Components include functional groups, alkyl groups, number of carbon atoms etc.

Alkyl Group

  • An alkane missing one hydrogen atom.

Basic Rules of IUPAC Nomenclature of Alkanes and Alkenes

  • Identify the longest continuous hydrocarbon chain.
  • Number the chain.
  • Identify substituents (alkyl groups etc.).
  • Name and locate substituents.

Exercise 1 and 2:

  • Contains multiple questions to practice naming and drawing structures

Isomerism

  • Constitutional Isomers: Different connectivity of atoms even though molecular formula is same. Includes chain isomers, position isomers, and functional group isomers
  • Stereoisomers: Same connectivity of atoms, but different spatial arrangement.
    • Enantiomers: Non-superimposable mirror images.
    • Diastereomers: Not mirror images. Includes cis-trans or geometric isomers.

Organic Reactions and Chemical Reagents

  • Electrophile: Accepts an electron pair.
  • Nucleophile: Donates an electron pair.
  • Addition Reaction: Two reactants form one product in a saturated alkene.
  • Substitution Reaction: Two reactants form two products.
  • Elimination Reaction: A saturated reactant becomes an unsaturated product.
  • Rearrangement Reaction: One reactant becomes one product.

Types of organic reagents

  • Electrophiles:
  • Nucleophiles:
  • Radicals:

Reactions in Alkane

  • Free Radical Substitution:
  • Combustion: Burning in oxygen to produce CO2 & H2O.
  • Oxidation: Using oxidizing agents (e.g., KMnO4)
  • Pyrolysis: Thermal decomposition in the absence of oxygen
  • Halogenation: Replacement of Hydrogen by halogens

Reactions in Alkene

  • Catalytic Hydrogenation: Converting it into the alkane.
  • Halogenation (Addition): Halogens add to the double bonds of the alkene to create dihalides.
  • Addition of Hydrogen Halides (HX): HX adds to the double bonds.
  • Oxidation: Use acidic KMnO4 to convert to a diol.
  • Oxidative Cleavage: Use hot, concentrated KMnO4, the double bond is broken.
  • Polymerisation: Small alkenes combined to form polymers such as polyethylene or polypropylene.

Reactions in Benzene

  • Halogenation: Requires a catalyst (e.g., FeCl3)
  • Nitration: Requires sulfuric acid (catalyst), produces nitrobenzene.
  • Sulfonation: Requires sulfuric acid (catalyst), produces benzenesulfonic acid.
  • Friedel-Crafts Alkylation: Substitution of alkyl groups.
  • Friedel-Crafts Acylation: Substitution of acyl.
  • Combustion: Burns in oxygen to produce CO2 and H2O.
  • Oxidation of alkylbenzenes: Can only involve a benzylic H

IUPAC Nomenclature of Alkanes, Alkenes, and Benzene Derivatives, cycloalkanes

  • Names are based on the longest chain and the substituents, following specific naming rules
  • Numbering of carbon atoms.

Stability of Alkenes, Alkanes, and Benzene

  • Stability of molecules.

Exercises

  • Practice questions for each learning unit

Conclusion

  • End-of-unit summary of different classes of hydrocarbons and their reactions.

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Description

Test your knowledge on the structure and properties of benzene and its aromatic compounds. This quiz covers bond angles, hybridization, and various structural formulas. Ideal for students studying organic chemistry.

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