Organic Compounds: Cycloalkanes and Their Stereochemistry

Draw the structures of the following molecules: 

(a) trans-1-Bromo-3-methylcyclohexane 

(b) cis-1,2-Dimethylcyclobutane 

(c) trans-1-tert-Butyl-2-ethylcyclohexane

Look at the following structure of the female hormone estrone, and tell whether each of the two indicated ring-fusions is cis or trans.

Give IUPAC names for the following cycloalkanes

Draw structures corresponding to the following IUPAC names:

a) 1,1 dimethyl cyclooctane

b) 3-cyclobutyl hexane

c) 1,2 -dichloro cyclopentane

d) 1,2- dibromo, 5- methylcyclohexane

Name the following cycloalkane

Name the following substances, including the cis- or trans- prefix:

a)

b)

Name the following substances, including the cis- or trans- prefix (red-brown= Br):

Name the following substances, including the cis- or trans- prefix (redbrown= Br):

Prostaglandin ${\mathbf{F}}_{\mathbf{2}\mathbf{\alpha }}$, a hormone that causes uterine contraction during childbirth,has the following structure. Are the two hydroxyl groups $\mathbf{(}\mathbf{-}\mathbf{OH}\mathbf{)}$ on thecyclopentane ring cis or trans to each other? What about the two carbon chainsattached to the ring?

cis-1,2-Dimethylcyclopropane has more strain than trans-1,2-dimethylcyclopropane. How can you account for this difference? Which of the two compounds is more stable?

Each $\mathbf{H}\mathbf{\leftrightarrow }\mathbf{H}$ eclipsing interaction in ethane costs about 4.0 kJ/mol. Howmany such interactions are present in cyclopropane? What fraction of theoverall 115 kJ/mol (27.5 kcal/mol) strain energy of cyclopropane is due totorsional strain?

Two conformations of cis-1,3-dimethylcyclobutane are shown. What is the difference between them, and which do you think is likely to be more stable?

Two conformations of cis-1,3-dimethylcyclobutane are shown. What is the difference between them, and which do you think is likely to be more stable?

How many $\mathbf{H}\mathbf{\leftrightarrow }\mathbf{H}$ eclipsing interactions would be present if cyclopentanewere planar? Assuming an energy cost of 4.0 kJ/mol for each eclipsing interaction,how much torsional strain would planar cyclopentane have? Since themeasured total strain of cyclopentane is 26 kJ/mol, how much of the torsionalstrain is relieved by puckering?

Draw two different chair conformations of trans-1,4 dimethylcyclohexane, and label all positions as axial or equatorial.

Draw two different chair conformations of cyclohexanol (hydroxycyclohexane),showing all hydrogen atoms. Identify each position as axial orequatorial.

Look at Figure 4-12 on page 105, and estimate the percentages of axial andequatorial conformations present at equilibrium in bromocyclohexane.

Why do you suppose an axial cyano (–CN) substituent causes practically no 1,3-diaxial steric strain (0.4 kJ/mol)? Use molecular models to help with your answer.

Draw the more stable chair conformation of the following molecules, and estimate the amount of strain in each: cis-1-tert-Butyl-4-ethylcyclohexane

Draw the more stable chair conformation of the following molecules, and estimate the amount of strain in each: cis-1-Bromo-4-ethylecyclohexane.

Identify each substituent in the following compound as axial or equatorial, and tell whether the conformation shown is the more stable or less stable chair form (green = Cl) :

Which isomer is more stable, cis-decalin or trans-decalin? Explain.

Hydrocortisone, a naturally occurring hormone produced in the adrenal glands, is often used to treat inflammation, severe allergies, and numerous other conditions. Is the indicated $\mathbf{-}\mathbf{OH}$ group axial or equatorial?

cis-1, 2-Dimethylcyclobutane is less stable than its trans isomer, but cis-1, 3-dimethylcyclobutane is more stable than its trans isomer. Draw the most stable conformations of both, and explain.

Assume that you have a variety of cyclohexane substituted in the positions indicated. Identify the substituents as either axial or equatorial. For example, a 1, 2-cis relationship means that one substituent must be axial and one equatorial, whereas a 1, 2-trans relationship means that either substituent is axial or both are equatorial.

 (a) 1, 3-Trans disubstituted                (b) 1, 4-Cis disubstituted

 (c) 1, 3-Cis disubstituted                    (d) 1, 5-Trans disubstituted 

 (e) 1, 5-Cis disubstituted                     (f) 1, 6-Trans disubstituted

Draw the two chair conformations of cis-1-chloro-2-methylcyclohexane. Which is more stable, and by how much?

Draw the two chair conformations of trans-1-chloro-2-methylcyclohexane. Which is more stable?

Galactose, a sugar related to glucose, contains a six-membered ring in which all the substituents except the $\mathbf{-}\mathbf{OH}$ group, indicated below in red, are equatorial. Draw galactose in its more stable chair conformation.

The German chemist J. Bredt proposed in 1935 that bicycloalkenes such as 1-norbornene, which have a double bond to the bridgehead carbon, are too strained to exist. Explain.

Draw three isomers of trans-1, 2-dichlorocyclobutane, and label them as either constitutional isomers or stereoisomers.

Draw 1, 3, 5-trimethyl cyclohexane using a hexagon to represent the ring. How many cis-trans stereoisomers are possible?

A 1, 2-cis disubstituted cyclohexane, such as cis-1, 2-dichlorocyclohexane, must have one group axial and one group equatorial. Explain.

A 1, 2-trans disubstituted cyclohexane must have either both groups axial or both groups equatorial. Explain.

Name the following compound, identify each substituent as axial or equatorial, and tell whether the conformation shown is the more stable or less stable chair form

Why is a 1, 3-cis disubstituted cyclohexane more stable than its trans isomer?

Which is more stable, a 1, 4-trans disubstituted cyclohexane or its cis isomer?

A trisubstituted cyclohexane with three substituents—red, green, and blue—undergoes a ring-flip to its alternate chair conformation. Identify each substituent as axial or equatorial, and show the positions occupied by the three substituents in the ring-flipped form.

The following cyclohexane derivative has three red, green, and blue substituents. Identify each substituent as axial or equatorial, and identify each pair of relationships (red–blue, red-green, and blue-green) as cis or trans.

Glucose exists in two forms having a 36:64 ratio at equilibrium. Draw a Skeletal structure of each, describe the difference between them, and tell which of the two you think is more stable

Draw the five cycloalkanes with the formula ${\mathbf{C}}_{\mathbf{5}}{\mathbf{H}}_{\mathbf{10}}$.

Draw a stereoisomer of trans-1, 3-dimethylcyclobutane.

Draw two constitutional isomers of $cis-\mathbf{1},\mathbf{2}-\mathbf{dibromocyclopentane}$ .

Name the following cycloalkanes:

b. Name the following cycloalkanes:

In light of your answer to Problem 4-48, draw the two chair conformations of 1,1,3-trimethylcyclohexane and estimate the amount of strain energy in each. Which conformation is favored?

One of the two chair structures of cis-1-chloro-3-methylcyclohexane is more stable than the other by 15.5 kJ/mol (3.7 kcal/mol). Which is it? What is the energy cost of a 1,3-diaxial interaction between chlorine and a methyl group?

Cis-decalin is less stable than trans-decalin. Assume that the 1,3-diaxial interactions in cis-decalin are similar to those in axial methylcyclohexane [that is, one CH $\leftrightarrow$H interaction costs 3.8 kJ/mol (0.9 kcal/mol)], and calculate the magnitude of the energy difference between cis- and trans-decalin.

Question: Amantadine is an antiviral agent that is active against influenza type A infection. Draw a three-dimensional representation of amantadine, showing the chair cyclohexane rings.

Question: There are two different substances named trans-1,2-dimethylcyclopentane. What is the relationship between them?