Ch.3 - Structure and Stereochemistry of Alkanes

Wade9th EditionOrganic ChemistryISBN: 9780135213728Non è quello che usi tu?Cambia libro di testo

Wade 9th Edition

Ch.3 - Structure and Stereochemistry of Alkanes

Problema 29c,d

Capitolo 3, Problema 29c,d

Draw the two chair conformations of each of the following substituted cyclohexanes. In each case, label the more stable conformation.]
c. cis-1-ethyl-4-isopropylcyclohexane
d. trans-1-ethyl-4-methylcyclohexane

Guida verificata passo dopo passo

Identify the substituents on the cyclohexane ring. For cis-1-ethyl-4-isopropylcyclohexane, the substituents are an ethyl group at carbon 1 and an isopropyl group at carbon 4. For trans-1-ethyl-4-methylcyclohexane, the substituents are an ethyl group at carbon 1 and a methyl group at carbon 4.

Draw the basic chair conformation of cyclohexane. This involves drawing a six-membered ring in a staggered conformation, resembling a chair.

Place the substituents on the chair conformation. For the cis isomer, both substituents should be on the same side of the ring (either both axial or both equatorial). For the trans isomer, one substituent should be axial and the other equatorial.

Draw the second chair conformation by flipping the first chair. This involves converting axial positions to equatorial and vice versa. Ensure that the relative positions (cis or trans) of the substituents are maintained.

Determine the more stable conformation by evaluating steric hindrance. Generally, the conformation with the larger substituents in the equatorial position is more stable due to reduced steric strain.

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Chair Conformation

Chair conformation is a three-dimensional shape that cyclohexane adopts to minimize steric strain and torsional strain, making it the most stable conformation. It resembles a chair, with alternating axial and equatorial positions for substituents, which affects the stability of the molecule based on steric interactions.

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Understanding what a conformer is.

Axial and Equatorial Positions

In cyclohexane's chair conformation, substituents can occupy axial positions, which are perpendicular to the ring, or equatorial positions, which are parallel to the ring. Equatorial positions are generally more stable due to reduced steric hindrance, especially for larger substituents, influencing the overall stability of the conformation.

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04:02

Equatorial Preference

Cis and Trans Isomerism

Cis and trans isomerism refers to the relative orientation of substituents around a cyclohexane ring. In cis isomers, substituents are on the same side, while in trans isomers, they are on opposite sides. This spatial arrangement affects the stability and energy of the chair conformations, as steric interactions differ between the two isomers.

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Is the following cyclohexane cis or trans?

Pratica correlata

Domanda del libro di testo

Draw the most stable conformation of

b. trans-1-tert-butyl-2-methylcyclohexane.

1372

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Domanda del libro di testo

Draw the most stable conformation of

c. trans-1-tert-butyl-3-(1,1-dimethylpropyl)cyclohexane.

1462

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Domanda del libro di testo

Use your results from Problem 3-27 to complete the following table. Each entry shows the positions of two groups arranged as shown. For example, two groups that are trans on adjacent carbons (trans-1,2) must be both equatorial (e,e) or both axial (a,a).

910

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Domanda del libro di testo

a. Draw both chair conformations of cis-1,4-dimethylcyclohexane, and determine which conformer is more stable.

b. Repeat for the trans isomer.

c. Predict which isomer (cis or trans) is more stable.

2522

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Domanda del libro di testo

Draw the most stable conformation of

a. cis-1-tert-butyl-3-ethylcyclohexane.

1448