p-Nitrophenol and 2,6-dimethyl-4-nitrophenol both have a pKa of 7.15 but 3,5-dimethyl-4-nitrophenol has pKa of 8.25. Why 3,5-dimethyl-4-nitrophenol is much less acidic is to be explained. Concept introduction: Resonance delocalization occurs only when the molecule is planar facilitating the overlapping of the orbitals. If the substituent groups present prevent co-planarity of the molecule then resonance is not possible. pKa = -log Ka, where Ka is the dissociation constant of the acid. Thus a stronger acid has a low pKa value. To explain: Why 3,5-dimethyl-4-nitrophenol is much less acidic with pKa of 8.25 when compared to p-nitrophenol and 2,6-dimethyl-4-nitrophenol both of which have a pKa of 7.15.

Question

The table includes macrostates characterized by 4 energy levels (&) that are equally spaced but with different degrees of occupation. a) Calculate the energy of all the macrostates (in joules). See if they all have the same energy and number of particles. b) Calculate the macrostate that is most likely to exist. For this macrostate, show that the population of the levels is consistent with the Boltzmann distribution. macrostate 1 macrostate 2 macrostate 3 ε/k (K) Populations Populations Populations 300 5 3 4 200 7 9 8 100 15 17 16 0 33 31 32 DATO: k = 1,38×10-23 J K-1

Answer 1

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Chapter 17.SE, Problem 64AP

Interpretation Introduction

Interpretation:

p-Nitrophenol and 2,6-dimethyl-4-nitrophenol both have a pKa of 7.15 but 3,5-dimethyl-4-nitrophenol has pKa of 8.25. Why 3,5-dimethyl-4-nitrophenol is much less acidic is to be explained.

Concept introduction:

Resonance delocalization occurs only when the molecule is planar facilitating the overlapping of the orbitals. If the substituent groups present prevent co-planarity of the molecule then resonance is not possible.

pKa = -log Ka, where Ka is the dissociation constant of the acid. Thus a stronger acid has a low pKa value.

To explain:

Why 3,5-dimethyl-4-nitrophenol is much less acidic with pKa of 8.25 when compared to p-nitrophenol and 2,6-dimethyl-4-nitrophenol both of which have a pKa of 7.15.

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The table includes macrostates characterized by 4 energy levels (&) that are equally spaced but with different degrees of occupation. a) Calculate the energy of all the macrostates (in joules). See if they all have the same energy and number of particles. b) Calculate the macrostate that is most likely to exist. For this macrostate, show that the population of the levels is consistent with the Boltzmann distribution. macrostate 1 macrostate 2 macrostate 3 ε/k (K) Populations Populations Populations 300 5 3 4 200 7 9 8 100 15 17 16 0 33 31 32 DATO: k = 1,38×10-23 J K-1

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