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Ch.3 - Structure and Stereochemistry of Alkanes
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoWade 9th EditionCh.3 - Structure and Stereochemistry of AlkanesProblema 46a,b
Capitolo 3, Problema 46a,b

Draw the two chair conformations of each compound, and label the substituents as axial and equatorial. In each case, determine which conformation is more stable.
a. cis-1-ethyl-2-isopropylcyclohexane
b. trans-1-ethyl-2-isopropylcyclohexane

Guida verificata passo dopo passo
1
Start by drawing the basic chair conformation of cyclohexane. This involves drawing two parallel lines that represent the carbon backbone, with alternating axial and equatorial positions for substituents.
For cis-1-ethyl-2-isopropylcyclohexane, place the ethyl group at carbon 1 and the isopropyl group at carbon 2. Since the compound is cis, both substituents should be on the same side of the ring. Assign one substituent to an axial position and the other to an equatorial position, then switch them for the second conformation.
Label the substituents in each conformation as axial or equatorial. Remember that axial positions are perpendicular to the ring plane, while equatorial positions are roughly parallel to the ring plane.
Evaluate the stability of each conformation. Generally, the conformation with the larger substituent in the equatorial position is more stable due to reduced steric hindrance.
Repeat the process for trans-1-ethyl-2-isopropylcyclohexane. In this case, the substituents should be on opposite sides of the ring. Draw both chair conformations, label the substituents, and determine which conformation is more stable based on the positions of the substituents.

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Chair Conformation

Chair conformation is a three-dimensional shape that cyclohexane rings adopt to minimize steric strain and torsional strain. In this conformation, carbon atoms are staggered, reducing repulsion between hydrogen atoms. Understanding how to draw and interpret chair conformations is crucial for analyzing the stability of cyclohexane derivatives.
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Understanding what a conformer is.

Axial and Equatorial Positions

In a chair conformation, substituents on the cyclohexane ring can occupy axial or equatorial positions. Axial positions are perpendicular to the ring plane, while equatorial positions are roughly parallel. Substituents in equatorial positions generally experience less steric hindrance, making them more stable than those in axial positions.
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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 of the ring, while in trans isomers, they are on opposite sides. This orientation affects the stability and spatial arrangement of the chair conformations, influencing which conformation is more stable.
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Is the following cyclohexane cis or trans?
Pratica correlata
Domanda del libro di testo

Draw the two chair conformations of each compound, and label the substituents as axial and equatorial. In each case, determine which conformation is more stable.

c. cis-1-ethyl-3-methylcyclohexane

d. trans-1-ethyl-3-methylcyclohexane

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Draw the two chair conformations of each compound, and label the substituents as axial and equatorial. In each case, determine which conformation is more stable.

e. cis-1-ethyl-4-methylcyclohexane

f. trans-1-ethyl-4-methylcyclohexane

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Use a Newman projection about the indicated bond to draw the most stable conformer for each compound.

a. 3-methylpentane about the C2―C3 bond

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Use a Newman projection about the indicated bond to draw the most stable conformer for each compound.

b. 3,3-dimethylhexane about the C3―C4 bond

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Domanda del libro di testo

Using what you know about the conformational energetics of substituted cyclohexanes, predict which of the two decalin isomers is more stable. Explain your reasoning.

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a. Draw the two chair conformations of cis-1,3-dimethylcyclohexane, and label all the positions as axial or equatorial.

b. Label the higher-energy conformation and the lower-energy conformation.

c. The energy difference in these two conformations has been measured to be about 23 kJ (5.4 kcal) per mole. How much of this energy difference is due to the torsional energy of gauche relationships?

d. How much energy is due to the additional steric strain of the 1,3-diaxial interaction?

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