Ch.3 - Structure and Stereochemistry of Alkanes

Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook

Wade 9th Edition

Ch.3 - Structure and Stereochemistry of Alkanes

Problem 52b

Chapter 3, Problem 52b

This is a Newman projection of a substituted cyclohexane.
b. Draw the equivalent structure using wedge and dash notation on a cyclohexane hexagon.

Verified step by step guidance

Identify the front and back carbon atoms in the Newman projection. The front carbon is the one closer to the viewer, and the back carbon is the one further away.

Determine the substituents on the front carbon. In the Newman projection, the front carbon has a bromine (Br) atom, two hydrogen (H) atoms, and is connected to the back carbon.

Determine the substituents on the back carbon. The back carbon has a methyl group (CH₃), two hydrogen (H) atoms, and is connected to the front carbon.

Draw the cyclohexane ring using a hexagon. Place the substituents on the appropriate carbon atoms using wedge and dash notation. Wedges indicate bonds coming out of the plane towards the viewer, and dashes indicate bonds going behind the plane.

Position the bromine and methyl group on the cyclohexane ring. Since the bromine is on the front carbon, it will be on one of the axial or equatorial positions, and the methyl group on the back carbon will be similarly positioned. Ensure the correct stereochemistry is represented.

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Key Concepts

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

Newman Projections

Newman projections are a way to visualize the conformation of a molecule by looking straight down the bond connecting two carbon atoms. This representation helps in understanding steric interactions and torsional strain between substituents on adjacent carbons, which is crucial for predicting the stability of different conformations in cyclic compounds like cyclohexane.

Wedge and Dash Notation

Wedge and dash notation is a method used to depict three-dimensional structures of molecules on a two-dimensional surface. Solid wedges represent bonds that project out of the plane towards the viewer, while dashed lines indicate bonds that extend behind the plane. This notation is essential for accurately representing the spatial arrangement of substituents in cyclohexane derivatives.

Cyclohexane Conformation

Cyclohexane can adopt several conformations, with the chair conformation being the most stable due to minimized steric strain. Understanding the different conformations, including axial and equatorial positions of substituents, is vital for predicting the reactivity and stability of substituted cyclohexanes, as seen in the question's context.

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Related Practice

Textbook Question

Conformational studies on ethane-1,2-diol (HOCH₂–CH₂OH) have shown the most stable conformation about the central C―C bond to be the gauche conformation, which is 9.6 kJ/mol (2.3 kcal/mol) more stable than the anti conformation. Draw Newman projections of these conformers, and explain this curious result.

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Textbook Question

The most stable form of the common sugar glucose contains a six-membered ring in the chair conformation with all the substituents equatorial. Draw this most stable conformation of glucose.

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Textbook Question

This is a Newman projection of a substituted cyclohexane. a. Draw the equivalent chair form.

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Textbook Question

This is a Newman projection of a substituted cyclohexane.

c. Give the IUPAC name.

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