Chemistry of Alkynes Quiz
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Questions and Answers

What is the general formula for alkynes?

  • C_nH_{2n-2} (correct)
  • C_nH_{2n}
  • C_nH_{2n+2}
  • C_nH_{n}

    • Alkynes can have cis-trans isomerism.

    False

    What type of bond do alkynes contain?

    Triple bond

    The two types of bonds present in an alkyne are ___ bonds.

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

    Match the following terms related to alkynes with their descriptions:

    <p>sp hybridization = Type of hybridization in alkynes Linear = Geometric arrangement of alkynes Alkynes = Hydrocarbons with at least one triple bond U.S. organic chemistry exam = ACS Exam</p> Signup and view all the answers

    Which of the following statements about alkyne nomenclature is correct?

    <p>The longest carbon chain must contain the triple bond.</p> Signup and view all the answers

    Alkynes are less reactive than alkenes.

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

    In alkyne nomenclature, if there is more than one triple bond, prefixes such as di, tri, or ___ are used.

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

    What term describes the result of a terminal alkyne reacting with a strong base such as sodium amide?

    <p>Deprotonation to create an acetylide ion</p> Signup and view all the answers

    Terminal alkynes are less acidic than other hydrocarbons due to their sp hybridization.

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

    What is the IUPAC name for a hydrocarbon with a terminal alkyne and one alcohol functional group?

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

    Acetylene is classified as a(n) ________ because it contains a triple bond between two carbon atoms.

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

    Match the following terms related to alkynes with their correct descriptions:

    <p>Terminal alkyne = An alkyne with at least one hydrogen atom attached to a sp hybridized carbon Acetylide ion = A strong nucleophile derived from terminal alkynes after deprotonation Nucleophilic attack = A reaction where a nucleophile attacks an electrophile to form a new bond SN2 reaction = A mechanism for substitution involving primary alkyl halides and acetylide ions</p> Signup and view all the answers

    Which type of alkyne can be synthesized through nucleophilic attack of an acetylide ion?

    <p>Substituted alkyne</p> Signup and view all the answers

    What is the end product of the hydration of an internal alkyne using mercuric sulfate and sulfuric acid?

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

    Alkynes are soluble in water due to their polar nature.

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

    Hydroboration–oxidation adds H—OH in an anti-Markovnikov orientation for alkynes.

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

    The ________ bonds in a triple bond consist of one sigma bond and two pi bonds.

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

    What type of alkyl borane is used to prevent double addition of borane to the triple bond during hydroboration–oxidation?

    <p>Hindered alkyl borane</p> Signup and view all the answers

    The driving force for tautomerization is making _____

    <p>C=O</p> Signup and view all the answers

    Match the following reagents with their respective roles in hydration:

    <p>HgSO4 = Catalyst for hydration H2SO4 = Acidic medium NaOH = Oxidative agent H2O2 = Source of hydroxyl group</p> Signup and view all the answers

    Which of the following catalysts is known as Lindlar's catalyst?

    <p>Powdered barium sulfate coated with palladium poisoned with quinoline</p> Signup and view all the answers

    Hydrogenation of alkynes produces trans alkenes.

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

    What is the rearrangement product of alkynes when hydrated using hydroboration-oxidation?

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

    Alkynes react faster than alkenes due to the stability of the vinyl cation intermediate.

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

    What is the first step in the reduction of an alkyne to an alkene using sodium and ammonia?

    <p>An electron adds to the alkyne, forming a radical anion.</p> Signup and view all the answers

    In the Zipper Reaction, internal alkynes can be isomerized to __________ alkynes using a strong base.

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

    In hydroboration–oxidation, to which carbon does borane add when using a terminal alkyne?

    <p>Least substituted carbon</p> Signup and view all the answers

    Match the following reactions with their products:

    <p>H2, Lindlar catalyst = Cis alkene Na, NH3 = Radical anion Br2 = Dibrominated alkene Hg(OAc)2, H2O = Alcohol</p> Signup and view all the answers

    What occurs during the hydrogenation of an alkyne?

    <p>Two moles of hydrogen are added, resulting in an alkane.</p> Signup and view all the answers

    Alkynes are considered electron-poor molecules.

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

    What type of stereochemistry is produced when hydrogen is added to an alkyne using Lindlar's catalyst?

    <p>Cis stereochemistry</p> Signup and view all the answers

    What type of isomers are enol and ketone/aldehyde classified as?

    <p>Structural isomers</p> Signup and view all the answers

    Oxidative cleavage of alkenes produces aldehydes and ketones.

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

    What is produced when KMnO4 is used to oxidize a terminal alkyne?

    <p>keto-acid</p> Signup and view all the answers

    In ozonolysis of alkynes, the final products are ________ acids.

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

    Match the following reactions with their outcomes:

    <p>Ozonolysis of alkenes = Aldehydes and ketones KMnO4 on terminal alkynes = Keto-acid KMnO4 on internal alkynes = Diketone Bromination of alkynes = Vinyl dihalides</p> Signup and view all the answers

    Which reagent is specifically used for ozonolysis?

    <p>O3</p> Signup and view all the answers

    Adding two moles of HX to an alkyne yields a geminal dihalide.

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

    What happens to internal alkynes when treated with a dilute neutral solution of KMnO4?

    <p>They are oxidized to a diketone.</p> Signup and view all the answers

    Study Notes

    Course Information

    • Course name: Chemistry 232, Organic Chemistry II
    • Course assignments include: Topic 1 Quiz (Chapter 9), Exam I (Chapters 10, 11, 14), Exam II (Chapters 15, 16, 17), Exam III (Chapters 18 and 19), Exam IV (Chapters 20, 21, 22), ACS Exam, Homework (HW), and Participation.
    • Exams are closed-book and closed-note.
    • A reaction sheet will be provided.

    Homework Guidelines

    • Homework consists of 50-100 questions per chapter.
    • Questions can originate from participation, review packets, and old exams.
    • Students must include the source of the problem.
    • Questions must include a one-to-two sentence rationale for the correct answer.
    • The average number of questions per day should be approximately 10.

    Topic 1 Quiz (Spring 2021 Version A #14)

    • Question: Which reason best explains why K>1 for the following reaction?
    • Possible Answers: The conjugate base of 2-butyne is stronger due to hybridization, is weaker due to hybridization, is stronger due to resonance, is weaker due to resonance
    • Correct Answer: The conjugate base of 2-butyne is a stronger base due to resonance.

    Chapter 9

    • Topics include: Structure of Alkynes, Alkyne Nomenclature, Properties and Spectroscopy of Alkynes, Alkyne Synthesis and Alkyne Reactions, and Synthesis Practice.

    Introduction to Alkynes

    • Alkynes contain a triple bond.
    • General formula: CnH2n-2
    • Each triple bond represents two degrees of unsaturation.
    • Similar to alkenes, they undergo addition and oxidation reactions.
    • Alkynes also have specific reactions, one example is substitution.

    Structure of Alkynes

    • Triple bond
    • Linear structure.
    • sp hybridization
    • No cis-trans isomers
    • π bonds are perpendicular to each other.
    • More reactive than alkenes.
    • Useful intermediates in organic synthesis.

    IUPAC Nomenclature

    • Find longest chain containing the triple bond.
    • Change -ane ending to -yne.
    • Number the chain from the end closest to the triple bond.
    • Number branches to locate their position.
    • If more than one triple bond, use di, tri, tetra, etc. to indicate the number of triple bonds
    • At least 9 carbons are required for cycloalkynes

    Multiple Functional Groups

    • If there is an alkene, the alkyne takes the lower number/priority
    • If numbering is equal, start with alkene (alphabetical)

    Physical Properties of Alkynes

    • Nonpolar
    • Insoluble in water
    • Soluble in most organic solvents.
    • Boiling points similar to alkanes of the same size.
    • Less dense than water.
    • Gases up to four carbons at room temperature.
    • Four carbons or less are gases at room temperature

    Synthesis of Alkynes

    • Double elimination: From alkane or alkene using Br2, UV light to form an alkyne. Followed by excess NaNH2, and workup with H2O.
    • Alkyne-Substituted Compounds: Acetylide ions attack unhindered alkyl halides, performing SN2 reactions to lengthen the alkyne chain.

    Other Topics

    • HW Grading: 5 points for completion (100 problems), 5 points for accuracy and format.
    • Participation Policy: Participation worksheets are due on Mondays, with participation questions in the Explore Review. Testmoz links will be posted. Do not post questions on Chegg.
    • Acetylide Ions in SN2 Reactions: Synthesis of substituted alkynes by nucleophilic attack on unhindered alkyl halides. SN2 reactions performed on primary alkyl halides to lengthen the alkyne chain.
    • Acidity of Alkynes: Terminal alkynes are more acidic than other hydrocarbons due to higher s-character in the sp hybridized carbon (stabilized by the adjacent positive nucleus)
    • Birch reduction: The alkyne undergoes a trans reduction to form a trans alkene. Hydrogen atoms come from the ammonia.
    • Oxidative Cleavage of Alkynes: Using KMnO4 under neutral conditions to convert alkynes into diketones (internal alkynes) or keto acids (terminal alkynes).
    • Oxidative Cleavage of Alkynes (Basic Conditions) or (Warmed): Creates two molecules of carboxylic acids from alkynes.
    • Ozonolysis: Uses ozone (O3) to cleave the alkyne and produce carboxylic acids.
    • Additional information on various reaction mechanisms relating to Alkynes and Alkynes reactions including addition of halogens (Br2 and Cl2), addition of HX (HCl, HBr, HI)
    • Enols-Ketones tautomerization: Formation of enol and ketone forms, including the mechanism.

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    Organic Chemistry II Course Assignment - Chapter 9 PDF

    Description

    Test your knowledge on alkynes, including their structures and properties. This quiz covers key topics such as isomerism, nomenclature, and chemical reactivity of alkynes. Perfect for chemistry students looking to reinforce their understanding of these hydrocarbons.

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