A. List the following carboxylic acids in order from...

a. List the following carboxylic acids in order from strongest acid to weakest acid: $$ \begin{array}{cccc} \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{COOH} & \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CHCOOH} & \mathrm{ClCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{COOH} & \mathrm{CH}_{3} \mathrm{CHCH}_{2} \mathrm{COOH} \\ K_{\mathrm{a}}=1.52 \times 10^{-5} & \mathrm{Cl} & K_{\mathrm{a}}=2.96 \times 10^{-5} & \mathrm{Cl} \\ & K_{\mathrm{a}}=1.39 \times 10^{-3} & & K_{\mathrm{a}}=8.9 \times 10^{-5} \end{array} $$ b. How does the presence of an electronegative substituent such as $\mathrm{Cl}$ affect the acidity of a carboxylic acid? c. How does the location of the substituent affect the acidity of the carboxylic acid?

a. List the following carboxylic acids in order from strongest acid to weakest acid:
$$
\begin{array}{cccc}
\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{COOH} & \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CHCOOH} & \mathrm{ClCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{COOH} & \mathrm{CH}_{3} \mathrm{CHCH}_{2} \mathrm{COOH} \\
K_{\mathrm{a}}=1.52 \times 10^{-5} & \mathrm{Cl} & K_{\mathrm{a}}=2.96 \times 10^{-5} & \mathrm{Cl} \\
& K_{\mathrm{a}}=1.39 \times 10^{-3} & & K_{\mathrm{a}}=8.9 \times 10^{-5}
\end{array}
$$
b. How does the presence of an electronegative substituent such as $\mathrm{Cl}$ affect the acidity of a carboxylic acid?
c. How does the location of the substituent affect the acidity of the carboxylic acid?

Key Concepts

Acid Strength

Acid strength refers to the tendency of an acid to donate a proton (H?) in solution. It is quantitatively measured using the acid dissociation constant (Ka) or its logarithmic counterpart, pKa. A lower pKa value indicates a stronger acid because it has a greater tendency to lose its proton, while a higher pKa corresponds to a weaker acid.

Acid Dissociation Constant (Ka) and pKa

The acid dissociation constant (Ka) is a numerical value that represents the equilibrium concentration of products and reactants when an acid dissociates in water. pKa is the negative logarithm of Ka and is used to easily compare acid strengths. These concepts are critical for understanding the relative strengths of different acids in organic and inorganic chemistry.

Inductive Effect

The inductive effect is a phenomenon in which electron density is shifted through sigma bonds in a molecule due to the presence of electronegative atoms or groups. This effect can stabilize or destabilize charged species, such as the conjugate base of an acid. In the context of carboxylic acids, electron-withdrawing groups via the inductive effect help stabilize the negative charge on the conjugate base, thereby enhancing the acid's strength.

Electronegative Substituents

Electronegative substituents, like chlorine, attract electron density toward themselves. When attached to a molecule, they can withdraw electrons through the inductive effect. In carboxylic acids, this electron withdrawal stabilizes the neighboring carboxylate anion, increasing the overall acidity of the acid.

Substituent Position Effects

The position of substituents relative to the carboxyl group significantly influences the inductive effect. Substituents that are closer to the carboxyl group exert a stronger electron-withdrawing effect, hence more effectively stabilizing the conjugate base. Conversely, substituents located farther away will have a diminished effect, resulting in comparatively lower acid strengths.

Transcript

00:01 In this question we have been given four different assets along with their respective ca values and we need to list the given carboxylic acids from the strongest acid to the weakest acid now the concept being used here is that of equilibrium constant or we can say ca now this can also be known as the ionization constant of an acid ionization constant of an acid where this a in the subscript clearly denotes the acid so here we can see that if we have an acid which is denoted as ha and it dissociates to give out h plus and also a negative here we can say that the equilibrium constant of this reaction or this equilibrium would be the concentration of h plus multiplied by the concentration of a negative divided by the concentration of ha because these are these two are the concentration terms of the products while this one is for the reactant this one is for the reactant so we can say that's since the value of k or since the expression for k is obtained, we can clearly say that since the value of k is directly proportional to the concentration of h plus, which is clearly visible in this particular expression, we can say that if ka is higher, the concentration of h plus would also be higher, and hence we can say that the acidity would also be higher.

01:21 Similarly, if ka value is lower, we can say that the overall concentration of h plus would also be smaller, and that is why the acidity of the solution would be weaker.

01:30 So here we can say that in the given question we have been given four assets along with their k -a values so if we just simply arrange these assets in the in the values or in the order of their decreasing k -a values we can simply say that we have firstly ch3 ch2 c -h cl and then we have c -o -o -h and the second acid or we can say the asset that has the second highest value of k -a would be equal to ch3 chc l then we have ch2 and cooh this would be followed by cl ch2 ch2 ch2 ch2 ch2 cooh and lastly the least strong acid would be ch3 ch2 ch2 ch2 and cooh so this is how we have figured out the correct order of the given carbonic acid from the strongest one to the weakest one now the second subpart of this question says that we need to explain how does the presence of an electronegative substituent affect the acidity so when these acid or we can say when a particular acid let us say ch3 ch2 chl and cooh which is the strongest acid as we have seen earlier so now if it dissociates what we have is ch3 ch2 chcl then we have c o negative or we can also write it in a little expanded form and we can write it as c double bond o negative and also the hydrogen ketion.

03:06 Here we can say that the overall molecule or overall this part contains negative charge and since we know that higher the charge means lower the stability of conjugate base or any species in general...

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