Chapter 3, Problem 73CP

Interpretation Introduction

Interpretation:

The most acidic compound from the given two compounds has to be determined.

Concept Introduction:

Using $p{K}_a$values to compare Acidity: In general, acid-base reaction said to reach equilibrium; the position of equilibrium is described by the term $K_{eq}$. When an acid-base reaction is carried out in aqueous solution, the new term arrives by the term $K_a$.

$p{K}_a=-log{K}_a$

$p{K}_a$ Values are used as measure of acidity; a strong acid will have a low $p{K}_a$ and a weak acid will have a high $p{K}_a$.

Using $p{K}_a$values to compare Basicity:  $p{K}_a$ Values are also used to compare bases; by drawing the conjugate acid of each base and compare the $p{K}_a$ values and identify the stronger base.

Bronsted-Lowry Acidity: Qualitative analysis; without using ${\text{pK}}_{\text{a}}$ values, the acids are compared by their structures.

Conjugate base stability: As the acid deprotonates, the stability of conjugate base formed is analyzed on the basis of electronegativity, size of the atom, inductive effect and orbitals.

Factors affecting the stability of Negative charges:

• Compare the atoms bearing the negative charge. If the negative charge is on high electronegative atom, more the conjugate base is stabilized and the compound readily donates proton.
• Compare the atoms in the same column. If the negative charge is in the same column of periodic table, no more electronegativity will be the dominant effect. Instead dominant effect is SIZE. Larger the size of the atom, better stabilize a negative charge by that atom.\
• Resonance: Resonance effect (delocalization of electrons over the alternative double bond system) that makes the conjugate base more stable than rest.

Curved arrows: Curved arrows are used to show the direction of electrons movement. It has a tail (the source of electrons, usually lone pair or bonding pair from a sigma or pi-bond) and head (the destination of electrons, usually forming new lone pair on atom or a new bond). Electrons always flow from high electron density to low electron density.