Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure

Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook

Bruice 8th Edition

Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure

Problem 45

Chapter 4, Problem 45

Draw 1,2,3,4,5,6-hexachlorocyclohexane with
a. all the chloro groups in axial positions.
b. all the chloro groups in equatorial positions.

Verified step by step guidance

Step 1: Begin by understanding the structure of cyclohexane. Cyclohexane is a six-membered ring that can adopt a chair conformation, which is the most stable conformation. In this conformation, each carbon atom has one axial position (pointing up or down, perpendicular to the ring) and one equatorial position (pointing outward, roughly parallel to the plane of the ring).

Step 2: For part (a), where all chloro groups are in axial positions, identify the six axial positions on the cyclohexane chair conformation. These alternate between pointing up and down around the ring. Place a chlorine atom at each of these axial positions.

Step 3: For part (b), where all chloro groups are in equatorial positions, identify the six equatorial positions on the cyclohexane chair conformation. These alternate between pointing outward and slightly upward or downward around the ring. Place a chlorine atom at each of these equatorial positions.

Step 4: Ensure that the placement of the chloro groups respects the stereochemistry of the chair conformation. Axial positions are perpendicular to the ring, while equatorial positions are angled outward. Double-check that all six chlorine atoms are correctly placed in either axial or equatorial positions as specified in parts (a) and (b).

Step 5: Draw the final structures for both cases. For part (a), the structure will show all chlorine atoms in axial positions, alternating up and down. For part (b), the structure will show all chlorine atoms in equatorial positions, alternating outward and slightly upward or downward. Label the positions clearly to avoid confusion.

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Key Concepts

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

Chair Conformation of Cyclohexane

Cyclohexane can adopt a chair conformation that minimizes steric strain. In this conformation, substituents can occupy either axial (pointing up or down) or equatorial (pointing outward) positions. The arrangement of substituents affects the stability of the molecule, with equatorial positions generally being more stable due to reduced steric hindrance.

Axial vs. Equatorial Substituents

In cyclohexane derivatives, substituents can be positioned axially or equatorially. Axial substituents are aligned parallel to the axis of the ring, while equatorial substituents extend outward from the ring. The choice of position significantly influences the molecule's overall stability and reactivity, as axial substituents can lead to 1,3-diaxial interactions, increasing steric strain.

Stereoisomerism in Substituted Cyclohexanes

Stereoisomerism occurs when compounds have the same molecular formula but differ in the spatial arrangement of atoms. In the case of hexachlorocyclohexane, the positioning of the six chlorine atoms can lead to different stereoisomers, depending on whether they are all in axial or equatorial positions. Understanding these arrangements is crucial for predicting the physical and chemical properties of the compound.

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Related Practice

Textbook Question

Is each of the following a cis isomer or a trans isomer?

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Textbook Question

Using Newman projections, draw the most stable conformer for each of the following:

c. 3,3-dimethylhexane, viewed along the C-3---C-4 bond

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Textbook Question

Verify the strain energy shown in Table 3.8 for cycloheptane

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Textbook Question

The chair conformer of fluorocyclohexane is 0.25 kcal/mol more stable when the fluoro substituent is in an equatorial position than when it is in an axial position. How much more stable is the anti conformer than a gauche conformer of 1-fluoropropane, considering rotation about the C1−C2 bond?

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Textbook Question

Using the data in Table 3.9, calculate the percentage of molecules of cyclohexanol that have the OH group in an equatorial position at 25 °C.

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Textbook Question

The bond angles in a regular polygon with n sides are equal to 180° - 360°/n

a. What are the bond angles in a regular octagon?

b. What are the bond angles in a regular nonagon?

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