CHM136H1 Lecture Notes - Lecture 12: Cyclohexane, Van Der Waals Strain, Stereoisomerism

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6 Feb 2016

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CHM136H1

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CHM136H1 Full Course Notes

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Prepare for midterm, composed of everything from first day to class before then. Methyl substituent replaces one of the hydrogen atoms, shown below. In equatorial position, there"s no steric strain from the methyl group despite the hydrogens. Axial position produces significant steric strain between methyl and two hydrogen atoms. Destabilizes the chair conformation due to the large cloud of electrons. 1,3 - where the conflicting atoms are located on the ring. For this strain, the g = 3. 8 kj/mol. The two conformations are not of equal energy. G = 7. 6 kj/mol needed to push it to the axial position. Table below gives strain present in common substituents in the axial position. 1,4-dimethylcyclohexane is shown below in its planar hexagonal representations. Next diagram is for the cis version in the chair conformation. Shows that one methyl is along the axis, and the other is on the equator. Next diagram is for the trans version in the chair conformation.

Related Questions

Conformational Analysis of Cyclohexane The following exercises can be completed using your lecture text as well as your class notes.

1. Draw both forms of the chair conformation of cyclohexane (right and left facing).

2. Draw a chair conformation of cyclohexane with only the axial hydrogen atoms shown.

3. Draw a chair conformation of cyclohexane with only the equatorial hydrogen atoms shown.

4. Draw the process of ring-flip of cyclohexane. Include both chair conformations and the boat conformation.

5. Draw a Newman projection of cyclohexane as viewed down the C1-C2, C5-C4 bonds.

6. Draw methylcyclohexane as a chair structure. Also show the ring-flip conformation of methylcyclohexane. Label each structure as high and low energy.

7. Draw methylcyclohexane using a Newman projection as viewed down the C1-C2, C5-C4 bonds. Show the ring-flip conformation also using a Newman projection. Label each as high or low energy. Indicate any interactions that are present in each structure (gauche, 1,3-diaxial, etc.)

8. Repeat the directions in exercise 7 for cis-1,2-dichlorocyclohexane.

9. Repeat the directions in exercise 7 for trans-1,2-dichlorocyclohexane.

10. Draw trans-1,3-dimethylcyclohexane using a Newman projection as viewed down the C1-C6, C3-C4 bonds. Show the ring-flip conformation also using a Newman projection. Label each as high or low energy. Indicate any interactions that are present in each structure (gauche, 1,3-diaxial, etc.)

11. Draw cis-1,3-dibromocyclohexane using a Newman projection as viewed down the C1-C6, C3-C4 bonds. Show the ring-flip conformation also using a Newman projection. Label each as high or low energy. Indicate any interactions that are present in each structure (gauche, 1,3-diaxial, etc.)

12. Draw trans-1-isopropyl-3-methylcyclohexane using a Newman projection as viewed down the C1-C6, C3-C4 bonds. Show the ring-flip conformation also using a Newman projection. Label each as high or low energy. Indicate any interactions that are present in each structure (gauche, 1,3-diaxial, etc.)

CHM136H1 Lecture Notes - Lecture 12: Cyclohexane, Van Der Waals Strain, Stereoisomerism

CHM136H1 Full Course Notes

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