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Ch.9 - Alkynes
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh.9 - AlkynesProblem 30a,b,c
Chapter 9, Problem 30a,b,c

Using cyclooctyne as your starting material, show how you would synthesize the following compounds. (Once you have shown how to synthesize a compound, you may use it as the starting material in any later parts of this problem.)
(a) cis-cyclooctene
(b) cyclooctane
(c) trans-1,2-dibromocyclooctane

Verified step by step guidance
1
Step 1: To synthesize cis-cyclooctene (a), start with cyclooctane. Perform a dehydrohalogenation reaction. First, brominate cyclooctane using Br₂ in the presence of UV light to form bromocyclooctane. Then, treat bromocyclooctane with a strong base, such as KOH or NaOH, to eliminate HBr and form cis-cyclooctene. The stereochemistry of the product will favor the cis-isomer due to the ring strain in an 8-membered ring.
Step 2: To synthesize cyclooctane (b), you can hydrogenate cis-cyclooctene. Use H₂ gas in the presence of a metal catalyst, such as Pd/C or Pt, under mild conditions. This will add hydrogen across the double bond, converting cis-cyclooctene into cyclooctane.
Step 3: To synthesize trans-1,2-dibromocyclooctane (c), start with cis-cyclooctene. Perform a bromination reaction by treating cis-cyclooctene with Br₂ in an inert solvent like CCl₄. This reaction proceeds via a bromonium ion intermediate, and the anti-addition mechanism ensures that the two bromine atoms add to opposite sides of the ring, resulting in the trans-isomer.
Step 4: Ensure the stereochemistry of the products is correct. For trans-1,2-dibromocyclooctane, verify that the bromine atoms are on opposite sides of the ring (anti-periplanar). This can be confirmed using spectroscopic techniques such as NMR.
Step 5: Review the overall synthetic pathway to ensure that each step logically follows from the previous one and that the reagents and conditions used are appropriate for the transformations described.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Synthesis of Organic Compounds

Synthesis in organic chemistry refers to the process of creating complex molecules from simpler ones through various chemical reactions. Understanding the mechanisms and pathways for synthesizing specific compounds, such as cis-cyclooctene or trans-1,2-dibromocyclooctane, is crucial for manipulating molecular structures and achieving desired chemical properties.
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Defining meso compounds.

Cyclic Compounds

Cyclic compounds are molecules that contain a ring structure, which can significantly influence their chemical behavior and reactivity. In this context, both cyclooctane and cis/trans-cyclooctene are cyclic hydrocarbons, and their structural differences (such as double bonds and stereochemistry) affect their physical and chemical properties, including stability and reactivity.
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Stereochemistry

Stereochemistry is the study of the spatial arrangement of atoms in molecules and how this affects their chemical behavior. The distinction between cis and trans isomers, as seen in trans-1,2-dibromocyclooctane, is a key aspect of stereochemistry, influencing properties like boiling points and reactivity, which are essential for understanding the outcomes of chemical reactions.
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Related Practice
Textbook Question

Using cyclooctyne as your starting material, show how you would synthesize the following compounds. (Once you have shown how to synthesize a compound, you may use it as the starting material in any later parts of this problem.)

(i)

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Textbook Question

Using hex-1-ene as your starting material, show how you would synthesize the following compounds. (Once you have shown how to synthesize a compound, you may use it as the starting material in any later parts of this problem.)

d. hex-2-yne

e. hexan-2-one

f. hexanal

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Textbook Question

Using hex-1-ene as your starting material, show how you would synthesize the following compounds. (Once you have shown how to synthesize a compound, you may use it as the starting material in any later parts of this problem.)

g. pentanoic acid

h. pentanal

i. undec-6-yn-5-ol

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Textbook Question

Using hex-1-ene as your starting material, show how you would synthesize the following compounds. (Once you have shown how to synthesize a compound, you may use it as the starting material in any later parts of this problem.)

a. 1,2-dibromohexane

b. hex-1-yne

c. 2,2-dibromohexane

Textbook Question

Using cyclooctyne as your starting material, show how you would synthesize the following compounds. (Once you have shown how to synthesize a compound, you may use it as the starting material in any later parts of this problem.)

(h)

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Textbook Question

Using cyclooctyne as your starting material, show how you would synthesize the following compounds. (Once you have shown how to synthesize a compound, you may use it as the starting material in any later parts of this problem.)

(g) cyclooctane-1,2-dione

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