Following are the alternative chair conformations for trans-1-bromo-2-methylcycl
ID: 2127757 • Letter: F
Question
Following are the alternative chair conformations for trans-1-bromo-2-methylcyclohexane: Using the data for ?G for monosubstituted cyclohexanes at room temperature (25 degree C) and the representative value* for the gauche interaction of two equatorially positioned substituents in the 1,2-position: Calculate the difference in the Gibbs free energy between the second and first conformation including the algebraic sign kJ/mol Given your value in (a), calculate the percent of the chair, indicated as B, presented in an equilibrium mixture of the conformers at 25 degree C %Explanation / Answer
a) ?G = -2.4+ (-7.3) = - 9.7 kJ/mol (adding representative value* for the gauche interaction of two equatorially positioned substituents in the 1,2-position)
b) ?G = - RT lnK = -9.7 kJ/mol
- (8.314 J/Mol K)* (298 K) * lnK = -9.7 * 1000 J/mol
ln K = 3.915
K = e ^ (3.915) = 50 = [product] / [reactant] = [B]/[A]
ie B = 50 A
% B= B / (B+A) = 50A / (50 A+ A) = 50 / 51 = 0.9804 = 98.04%