Question

The partition coefficient (log 10P) provides a measure of the lipophilicity of a compound. P = [A]oct/[A]ag Using the data provided below, calculate the logP (at 298 K) for urea AG*solv(urea) in n-octanol = -45.7 kJ mol-1 AG* solv(urea) in water = -57.7 kJ mol-1 Select one: O a. 0.0079 O b.-2.10 O c. 126.60 d. 2.10

Please explain your answer

Answer 1

logP is related to $\Delta$G_transfer by the equation

----(1)

logP = -AGtransfer RTln 10

where  $\Delta$G_transfer is given by

$\Delta$​​​​​​​G_transfer =  $\Delta$​​​​​​​G_octanol -  $\Delta$​​​​​​​G_hydration

= - 45.7 + 57.7

= 12 kJ

substituting the value of  $\Delta$​​​​​​​G_transfer, R = 8.314 J and T = 298 K in equation (1) we get,

log P = -12000/(8.314*298*ln(10))

log P = -2.10

So the answer is option (b)