1.) Calculate the cis/trans equilibrium constant for a 1,3-disubstituted cyclohe
ID: 915088 • Letter: 1
Question
1.) Calculate the cis/trans equilibrium constant for a 1,3-disubstituted cyclohexane compound at 6.2 Kelvin, as shown below. The A value for substituent X is 6.7 kJ/mol, while the A value for substituent Y is 1.4 kJ/mol. Assume that the lowest-energy chairs of each stereoisomer are in equilibrium.
2.) Consider a solution containing a conformationally-locked ring system with a single substituent. Upon analysis at 255.0 K, the axial conformer is found to have a concentration of 4.03 mM, and the equatorial conformer is found to have a concentration of 8.5 mM. Given this, calculate the A value for this substituent in kJ/mol.
Please answer ASAP w/ full explanations!
Explanation / Answer
1) dG = -RTlnK
dA = dG
with,
K = equlibrium constant
dG = 6.7 - 1.4 = 5.3 kJ/mol
T = 6.2 K
R = 8.314 J/K.mol
feed values,
5.3 = -8.314 x 6.2 lnK
K = 0.9023
2) dA = dG = -RTlnK
[eq] = 8.5 mM
[ax] = 4.03 mM
T = 255 K
R = 8.314 J/K.mol
we get,
dG = -8.314 x 255 ln(8.5/4.03)
= -1.58 kJ/mol
So the A value for the substitutent would be 1.58 kJ/mol (a +ve value).
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