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Chapter 4: Problem 65

Write structural formulas for all of the possible cistrans isomers of the following compounds: a. \(1,2,3\) -trimethylcyclopropane b. 1,3 -dichlorocyclopentane c. \(1,1,3\) -trimethylcyclohexane d. (3-methylcyclobuty1)-3-methylcyclobutane

Short Answer

Expert verified
The structural formulas of the possible cis-trans isomers for the given compounds are as follows: a. \(1,2,3\)-trimethylcyclopropane has no cis-trans isomers due to its small ring size. b. 1,3-dichlorocyclopentane has two isomers: - cis-1,3-dichlorocyclopentane: ![cis-1,3-dichlorocyclopentane](https://i.imgur.com/ziE8ovf.png) - trans-1,3-dichlorocyclopentane: ![trans-1,3-dichlorocyclopentane](https://i.imgur.com/3qIpTJn.png) c. 1,1,3-trimethylcyclohexane has two isomers: - cis-1,1,3-trimethylcyclohexane: ![cis-1,1,3-trimethylcyclohexane](https://i.imgur.com/zZYousK.png) - trans-1,1,3-trimethylcyclohexane: ![trans-1,1,3-trimethylcyclohexane](https://i.imgur.com/TmR9Fn4.png) d. (3-methylcyclobutyl)-3-methylcyclobutane has two isomers: - cis-(3-methylcyclobutyl)-3-methylcyclobutane: ![cis-(3-methylcyclobutyl)-3-methylcyclobutane](https://i.imgur.com/TDyJhN0.png) - trans-(3-methylcyclobutyl)-3-methylcyclobutane: ![trans-(3-methylcyclobutyl)-3-methylcyclobutane](https://i.imgur.com/CWFJJv2.png)

Step by step solution

01

1a. Trimethylcyclopropane isomers

Since it is a cyclopropane molecule, there are no possible cis-trans isomers due to the small carbon ring size which leads to no geometric isomerism. Therefore, \(1,2,3\)-trimethylcyclopropane forms only one structure that is given below: ![1,2,3-trimethylcyclopropane](https://i.imgur.com/17Rwsbh.png)
02

1b. 1,3-dichlorocyclopentane isomers

In the case of 1,3-dichlorocyclopentane, two possible cis-trans isomers can be formed: (1) cis-1,3-dichlorocyclopentane: In this isomer, both chlorine atoms are located on the same side of the carbon ring. (2) trans-1,3-dichlorocyclopentane: In this isomer, chlorine atoms are located on opposite sides of the carbon ring. These isomers can be represented as follows: cis-1,3-dichlorocyclopentane: ![cis-1,3-dichlorocyclopentane](https://i.imgur.com/ziE8ovf.png) trans-1,3-dichlorocyclopentane: ![trans-1,3-dichlorocyclopentane](https://i.imgur.com/3qIpTJn.png)
03

1c. 1,1,3-trimethylcyclohexane isomers

Due to the presence of two methyl groups on carbon 1 and one on carbon 3, we obtain three possible cis-trans isomers for 1,1,3-trimethylcyclohexane: (1) cis-1,1,3-trimethylcyclohexane: In this isomer, carbon 3 methyl group is on the same side as the other two methyl groups. (2) trans-1,1,3-trimethylcyclohexane: In this isomer, the carbon 3 methyl group is on the opposite side of the other two methyl groups. The three isomers can be represented as follows: cis-1,1,3-trimethylcyclohexane: ![cis-1,1,3-trimethylcyclohexane](https://i.imgur.com/zZYousK.png) trans-1,1,3-trimethylcyclohexane: ![trans-1,1,3-trimethylcyclohexane](https://i.imgur.com/TmR9Fn4.png)
04

1d. (3-methylcyclobutyl)-3-methylcyclobutane isomers

For this compound, we will have two possible cis-trans isomers: (1) cis configuration: Both methyl groups are located on the same side of their respective carbon rings. (2) trans configuration: The methyl groups are located on the opposite sides of their respective carbon rings. These isomers can be represented as follows: cis-(3-methylcyclobutyl)-3-methylcyclobutane: ![cis-(3-methylcyclobutyl)-3-methylcyclobutane](https://i.imgur.com/TDyJhN0.png) trans-(3-methylcyclobutyl)-3-methylcyclobutane: ![trans-(3-methylcyclobutyl)-3-methylcyclobutane](https://i.imgur.com/CWFJJv2.png)

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Most popular questions from this chapter

(a) How many pairs of eclipsed hydrogen are present in planar cyclobutane? (b) In puckered cyclobutane ?

Would you expect cis- or trans-1, 2-dimethylcyclopropane to be the more stable? Explain.

You have two bottles labeled "1, 2-Cyclopentanediol," one containing a compound of m.p. \(30^{\circ}\), the other a compound of m.p. \(55^{\circ}\); both compounds are optically inactive. How could you decide, beyond any doubt, which bottle should be labeled "cis" and which "trans"?

(a) trans-1, 2-Dimethylcyclohexane exists about \(99 \%\) in the diequatorial conformation; trans-1, 2-Dibromocyclohexane on the other hand, exists about equally in diequatorial and diaxial conformations. Furthermore, the fraction of the diaxial conformation decreases with increasing polarity of the solvent. How do you account for the contrast between the dimethyl and dibromo compounds? (b) If trans-3-cis-4-dibromo-tert-butylcyclohexane is subjected to prolonged heating, it is converted into an equilibrium mixture (about \(50: 50\) ) of itself and a diastereomer. What is the diastereomer likely to be? How do you account for the approximately equal stability of these two diastereomers? [Here, and in (c), consider the more stable conformation of each diastereomer to be the one with an equatorial tert-buty1 group]. (c) There, are two more diastereomeric 3,4 -dibromo tert-butylcyclohexanes. What are they? How do you account for the fact that neither is present to an appreciable extent in the equilibrium mixture?

Write expanded structures showing the \(\mathrm{C}-\mathrm{C}\) bonds for each of the following condensed formulas. Name each substance by an accepted system. a. \(\left(\mathrm{CH}_{2}\right)_{10}\) (saturated compound only) b. \(\left(\mathrm{CH}_{2}\right)_{5} \mathrm{CHCH}_{3}\) (c) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}\left(\mathrm{CH}_{2}\right)_{6} \mathrm{CHC}_{2} \mathrm{H}_{5}\) d. The isomers of trimethylcyclobutane e. \(\left(\mathrm{CH}_{2}\right)_{6} \mathrm{CHCH}_{2} \mathrm{C}\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}_{2} \mathrm{CI}\) f. \(\left[\left(\mathrm{CH}_{2}\right)_{2} \mathrm{CH}\right]_{2} \mathrm{C}\left(\mathrm{CH}_{3}\right) \mathrm{C}_{2} \mathrm{H}_{5}\)
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