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Q.55.

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Organic Chemistry
Found in: Page 128

Short Answer

Question: For each compound drawn below:

a. Draw representations for the cis and trans isomers using a hexagon for the six membered ring, and wedges and dashed wedges for substituents.

b. Draw the two possible chair conformations for the cis isomer. Which conformation, if either, is more stable?

c. Draw the two possible chair conformations for the trans isomer. Which conformation, if either, is more stable?

d. Which isomer, cis or trans, is more stable and why?

Answer

a.

b.

c.

d.

See the step by step solution

Step by Step Solution

Step 1: Representation of chair conformation in the cis-trans hexagon

The conversion of chair conformation into cis-trans hexagon involves the following points:

  • The hexagon has six carbon atoms in a cyclic form.
  • The cis and trans hexagons are shown by representing the two groups by the same stereochemistry or opposite stereochemistry, depending on the location of the groups.

Step 2: Wedge dash representation of the chair conformation

The chair conformation can be represented into the wedge dash representation by showing the corresponding substituents above the or below the plane.

Step 3: Explanation

a.

The cis and trans hexagons of the given molecule are shown below:

Cis and trans hexagons

Cis and trans hexagons

Cis and trans hexagons

b.

The cis conformation has only up or only down substitution.

More stable cis conformation

More stable cis conformation

More stable cis conformation

c.

The trans conformation has up and down conformations.

More stable trans isomer

More stable trans isomer

More stable trans isomer

d.

A stable isomer is that in which the bulky groups are at equatorial positions.

Cis isomer is more stable due to the presence of all groups at the equatorial position

Trans isomer is more stable due to the presence of all groups at the equatorial position

Trans isomer is more stable due to the presence of all groups at the equatorial position

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