Free Radical Reactions in Chemistry
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Questions and Answers

What initiates the free radical chain reaction?

  • Chemical catalyst
  • Heat energy
  • UV light (correct)
  • Mechanical agitation

    • Which product is formed when a chlorine radical abstracts hydrogen from methane?

  • Methyl chloride
  • Chlorinated methane
  • Chlorine gas
  • Hydrochloric acid and methyl radical (correct)

    • What characterizes the termination step in a free radical chain reaction?

  • Free radicals continue to form
  • Free radicals are removed from the system (correct)
  • Energy absorption occurs
  • New radicals are created

    • During the second propagation step, what does the methyl radical do?

    <p>Reacts with a chlorine molecule</p> Signup and view all the answers

    What happens to the other chlorine atom during the second propagation step?

    <p>It becomes a free radical</p> Signup and view all the answers

    What type of bonds do alkanes contain?

    <p>Only carbon-to-carbon and carbon-to-hydrogen single bonds</p> Signup and view all the answers

    Which of the following is the correct general formula for alkanes?

    <p>CnH2n+2</p> Signup and view all the answers

    Which of the following hydrocarbons is an example of an alkane?

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

    How does the molecular size of alkanes affect their melting and boiling points?

    <p>They increase with size due to stronger intermolecular forces.</p> Signup and view all the answers

    What type of isomers does butane (C4H10) demonstrate?

    <p>Constitutional isomers with the same molecular formula but different connectivity</p> Signup and view all the answers

    What is the primary type of intermolecular force present in alkanes?

    <p>Van der Waals dispersion forces</p> Signup and view all the answers

    What prefix denotes a hydrocarbon with seven carbon atoms?

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

    What happens to the Van der Waals forces as alkane molecular size increases?

    <p>They increase due to the greater distance of valence electrons</p> Signup and view all the answers

    What is the effect of branching on the physical properties of alkanes?

    <p>Branching decreases surface area.</p> Signup and view all the answers

    Which statement is true regarding the boiling points of cycloalkanes compared to straight chain alkanes?

    <p>Cycloalkanes have higher boiling points than straight chain alkanes.</p> Signup and view all the answers

    What part of the IUPAC name identifies the substituent groups on the parent alkane?

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

    Which of the following best describes the nature of alkanes in terms of solubility?

    <p>Alkanes are non-polar and insoluble in polar solvents.</p> Signup and view all the answers

    What is the general formula for an alkyl group derived from alkanes?

    <p>CnH2n+1</p> Signup and view all the answers

    What forces are responsible for the solid-state characteristics of straight-chain alkanes?

    <p>Vander Waals forces</p> Signup and view all the answers

    Which of the following accurately describes the densities of alkanes?

    <p>Alkanes have densities near 0.7 g/mL and are less dense than water.</p> Signup and view all the answers

    In IUPAC nomenclature, which suffix indicates that a compound is a saturated hydrocarbon?

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

    What is the first step in IUPAC nomenclature for simple alkanes?

    <p>Identify the parent hydrocarbon</p> Signup and view all the answers

    When choosing between two chains of equal length, which chain should be selected as the parent?

    <p>The chain with more branch points</p> Signup and view all the answers

    How should the carbon atoms in the parent chain be numbered when the first branch point is determined?

    <p>Starting from the end closer to the first branch point</p> Signup and view all the answers

    What must be done when two substituents are located on the same carbon atom?

    <p>Give both the same number</p> Signup and view all the answers

    Which of the following is a correct practice when writing the IUPAC name?

    <p>Use commas for numbers and hyphens for prefixes</p> Signup and view all the answers

    What should be done when there are multiple identical substituents in the compound?

    <p>Use multiplier prefixes like di-, tri-, and tetra-</p> Signup and view all the answers

    How should a branched substituent be named in a branched alkane?

    <p>As a compound itself, referring to its structure</p> Signup and view all the answers

    What is correctly stated about the numerical prefix used when naming substituents?

    <p>The prefix has no role in the numerical designation</p> Signup and view all the answers

    What does the prefix 'n-' indicate in the nomenclature of alkanes?

    <p>A normal straight-chain alkane</p> Signup and view all the answers

    Which condition is necessary for the hydrogenation process of alkenes and alkynes?

    <p>Room temperature and atmospheric pressure</p> Signup and view all the answers

    What type of carbon is described as being attached to three other carbons?

    <p>Tertiary carbon</p> Signup and view all the answers

    What prefix signifies a carbon atom that is attached to two other carbons?

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

    Which of the following is the correct name for a cyclic hydrocarbon with the formula C3H6?

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

    Which of the following is true about the prefix 'iso'?

    <p>It specifies a straight chain with one branching carbon</p> Signup and view all the answers

    What is the common name for the alkyl group that has the molecular structure (CH3)3C-?

    <p>tert-butyl</p> Signup and view all the answers

    Which catalytic material is commonly used in the hydrogenation of alkenes and alkynes?

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

    What is the primary purpose of the Clemmensen reduction?

    <p>To convert carbonyl groups to methylene groups</p> Signup and view all the answers

    Which reaction involves the formation of a C-C σ-bond?

    <p>Wurtz reaction</p> Signup and view all the answers

    What happens during the oxidation of alkanes?

    <p>They release energy upon combustion</p> Signup and view all the answers

    In pyrolytic cracking, the key characteristic involves:

    <p>Thermal decomposition in the absence of air</p> Signup and view all the answers

    During free radical substitution reactions, which statement is true?

    <p>All hydrogens in a given alkane can be substituted</p> Signup and view all the answers

    What is the role of UV-light in the reaction between methane and chlorine?

    <p>To initiate the substitution reaction</p> Signup and view all the answers

    What components make up soda lime used in decarboxylation reactions?

    <p>Sodium Hydroxide and Calcium Oxide</p> Signup and view all the answers

    What type of reaction is characterized by a chain mechanism involving free radicals?

    <p>Substitution reaction</p> Signup and view all the answers

    Study Notes

    Alkanes and Cycloalkanes

    • Alkanes are the simplest organic compounds, composed of only carbon and hydrogen atoms
    • Alkanes have only carbon-to-carbon and carbon-to-hydrogen single bonds
    • Alkane naming follows a simple counting system (e.g., methane, ethane, propane, butane) corresponding to 1, 2, 3, and 4 carbons respectively.
    • The general formula for alkanes is CnH2n+2, where 'n' is the number of carbon atoms in the chain.
    • Pent- means 5, Hex- means 6, Hept- means 7, Oct- means 8, Non- means 9, and Dec- means 10 carbon atoms
    • Isomers are compounds with the same molecular formula but different structural formulas, leading to different properties. Butane (C4H10) exists as two isomers: butane and iso-butane.

    Intended Learning Outcomes (ILOs)

    • Students will gain an understanding of the physical properties of alkanes.
    • Students will have a good idea about the nomenclature of alkanes.
    • Students will learn methods to prepare alkanes.
    • Students will become familiar with alkane reactions.

    Contents

    • Alkane definition, formula, and structure
    • Physical characteristics of alkanes
    • Nomenclature of alkanes
    • Cycloalkanes properties and examples
    • Preparation of alkanes
    • Reactions of alkanes

    Hydrocarbons

    • Hydrocarbons are the simplest organic compounds, composed of carbon and hydrogen atoms
    • Alkanes are a type of hydrocarbon with only carbon-to-carbon and carbon-to-hydrogen single bonds.
    • Alkane naming follows a systematic pattern

    Physical Characteristics of Alkanes

    • The electronegativity difference between carbon and hydrogen is small (0.4), resulting in nonpolar C—H bonds.
    • The primary intermolecular forces are van der Waals dispersion forces.
    • The strength of these forces increases with the size of the molecule.
    • Melting and boiling points increase with molecule size due to stronger intermolecular forces. For straight-chain alkanes, the boiling point increases with increasing chain length/size.
    • Branching of the alkane chain decreases the surface area and therefore the strength of the van der Waals dispersion forces resulting in lower melting and boiling points.

    Van der Waals Dispersion Forces

    • This is the weakest type of intermolecular force
    • It occurs due to temporary fluctuations in electron distribution within a molecule resulting in temporary dipoles.
    • This temporary dipole affects nearby molecules, inducing further temporary dipoles
    • The strength of dispersion forces is directly related to the size and shape of the molecule

    Cycloalkanes

    • Cycloalkanes have similar properties to alkanes, but they have higher melting and boiling points than straight-chain alkanes due to increased surface contact.
    • Cycloalkanes are also insoluble in water, as they are nonpolar.
    • The solubility of cycloalkanes is in organic solvents.

    IUPAC Names for Alkanes

    • IUPAC (International Union of Pure and Applied Chemistry) system systematically names alkanes.
    • Alkane names have four parts: a Locant, Prefix, Parent, and Suffix.
      - Locant indicates the position of substituents - Prefix designates substituent groups - Parent indicates the main carbon chain length - Suffix denotes the presence of only single bonds.

    Alkyl Groups

    • Alkyl groups are created by removing a hydrogen atom from an alkane.
    • Alkyl groups have the general formula CnH2n+1.
    • They are named by replacing the -ane ending with -yl.

    IUPAC Nomenclature of Simple Alkanes

    • Step 1: Identify the parent hydrocarbon (longest carbon chain)
    • Step 2: Number the atoms in the longest chain, prioritizing the branch point closets to the end of the chain
    • Step 3: Identify and number the substituents (attaching groups) locating their attachment points.
    • Step 4: Write the name as a single word, using hyphens and commas for numbers as necessary
    • For identical substituents, use prefixes (di, tri, etc.)

    IUPAC Nomenclature of Branched Alkanes

    • Name the branched substituent as if it were a parent compound, numbered from the point of attachment to the main chain
    • The branched substituent is named and placed within parentheses
    • Use prefixes to indicate the number of repeated substituents

    Reactions of Alkanes

    • Alkanes are relatively unreactive, their carbon-carbon and carbon-hydrogen bonds are strong.
    • Alkanes can undergo oxidation/combustion reactions.
    • Combustion: When alkanes are burned with sufficient oxygen, they produce carbon dioxide and water, releasing energy.
    • Pyrolysis/cracking: Thermal decomposition of higher alkanes into smaller alkanes in the absence of oxygen.
    • Halogenation: free radical substitution of a hydrogen atom in the alkane with a halogen atom (e.g., Cl, Br).
    • Photochemical reaction: The reaction between methane and chlorine in the presence of UV light, yielding chloromethane through a free radical chain reaction.
      • Chain initiation step: UV light breaks apart chlorine to form chlorine free radicals
      • Chain propagation step: The free radical abstracts a hydrogen from methane and forms a new radical
      • Chain termination step: Two free radicals combine to form a stable compound.

    Nomenclature of Alkanes 2- Common Names

    • For alkanes beyond propane, straight-chain alkanes are sometimes indicated by the prefix n (for normal), to distinguish them from branched-chain alkanes.
    • The prefix iso is used to indicate that the chain has a branched structure, where all carbons do not form a straight chain, except one carbon.
    • The prefix neo is used with a branched structure where the carbon with the most substitutions is second to last carbon in the chain

    Common Names

    • Common names for alkyl groups such as isopropyl, sec-butyl, isobutyl, and tert-butyl, are also useful.

    Cycloalkanes

    • When carbon atoms join to form rings, these become cycloalkanes.
    • Cyclopropane, cyclobutane, cyclopentane, and cyclohexane are cycloalkanes that have rings of 3, 4, 5, and 6 carbon atoms respectively.
    • The general formula for cycloalkanes is CnH2n.

    Preparation of Alkanes

    • Catalytic reduction/hydrogenation: Alkynes and alkenes can be converted to alkanes by adding hydrogen in the presence of a transition metal catalyst.
    • Clemmensen reduction: Reduce carbonyl groups (aldehydes and ketones) into methylene groups using zinc amalgam and hydrochloric acid
    • Grignard's reagent: Hydrolyze an alkyl halide with magnesium and water to yield an alkane.
    • Wurtz reaction: Heating an alkyl halide with sodium metal to create alkyl-alkyl bonds and produce an alkane.
    • Soda lime reaction: Decarboxylation of carboxylic acids or their salts by heating with soda lime, producing an alkane

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    Alkanes and Cycloalkanes Lecture Notes PDF

    Description

    Test your knowledge on free radical chain reactions, focusing on initiation, propagation, and termination steps. This quiz covers key concepts such as the interaction between chlorine radicals and methane. Assess your understanding of how free radicals behave during chemical reactions.

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