Arrange the compounds in each of the following sets in order of increasing acidi
ID: 637069 • Letter: A
Question
Arrange the compounds in each of the following sets in order of increasing acidity a) formic acid, acetic acid, oxalic acid b) Fluoroacetic acid, 3-fluoropropanoic acid, iodoacetic acid c) benzoic acid, p-methoxybenzoic acid, p-nitrobenzoic acid II. Use the Henderson-Hasselbach equation to calculate the concentrations oflactate and lactic acid present in a 0.0010 M solution of lactic acid at physiological pH (7.3). The Ka of lactic acid i5 1.38 X 104 III. Show how you would convert 2-bromobutane into 2-methylbutanoic acid using both Grignard carboxylation and nitrile hydrolysis. IV. Show how to prepare each of the following from butanenitrile. Do not give the mechanism,but show the equations for each step. a) 1-butanol b) butylamine c) 2-methyl-3-hexanone V. A. Butanoic acid can be converted into each of the following; and each of the following can be converted into butanoic acid. Show how you would convert butanoic acid into each, and vice versa. a) 1-butanol b) 1-bromobutane c) 1-butene B. Show how to covert butanoic acid into a) pentanoic acid, and b) octane. C. Show how you would make butanoic acid from: a) 1-bromopropane, b) 4-octeneExplanation / Answer
1. Acidity= The acid is stronger when it can lose hydrogen easily to the base.
Acidity is the higer concentration of hydrogen ions. Thus lower pH value means higer acidity.
The more stable conjugate base of an acid, the more stable is the acid.
a. In formic acid, acetic acid and oxalic acid the acidity order is,
Oxalic acid > Formic acid > Acetic acid.
This is because, stabilizing and destabilizing factors of conjugate base.
Formic acid CH2O2, the conjugate base is CHOO-. Thus due to electronegativity the negative charge is more stable on an oxygen because its electronegative. Thus increases acidity than acetic acid.
But in Acetic acid CH3COOH, the conjugate base is CH3COO-. There is methyl group instead of hydrogen adjustant to carbonyl. The methyl group is electron donating group which can destabilize the conjugate base. Thus decreases the acidity than oxalic acid and formic acid.
In oxalic acid COOH-COOH there are two COOH groups, Thus on removing H+ ion, the O- can form hydrogen bond with hydrogen atom of other COOH group, This will stabilize the conjugate base and increases the acidity than formic acid and acetic acid.
Therefore Oxalic acid > Formic acid > Acetic acid
b. In Fluoroacetic acid, 3-floropropanoic acid and Iodoacetic acid,
Fluoroacetic acid C3H3FO2 and Iodoacetic acid C2H3IO2, Fluro is electron withdrawing than Iodo group. Acidity of a compound is measured by the ionization energy as well as stability of conjugate base. In fluroacetic acid and Iodoacetic acid ionization energy is same but conjugate base of fluoroacetic acid is more stabilize due to inductive effect of flourine as compared to iodine. (Inductive effect= electron withdrawing effect -I effect). Iodine is least electronegative in the series.
Therefore Fluoroacetic acid > Iodoacetic acid.
3-Fluropropanoic acid C3H5FO2 and Iodoacetic acid C2H3IO2. Inductive effect decreases the acidity. Acetic acid have methyl group should have higher +I effect than ethyl group in propanoic acid. +I effect of methyl group in Iodoacetic acid makes it less acidic as the polarity of O-H bond decreases than propanoic acid with ethyl group which has less +I effect.
Therefore 3-fluropropanoic acid > Iodoacetic acid.
Fluroacetic acid C3H3FO2 and 3-fluropropanoic acid C3H5FO2 . Fluroacetic acid is highly electronegative than flouropropanoic acid. In fluroacetic acid F atom is closer to the carboxyllic group than fluoropropanoic acid. thus fluroacetic acid has higher acidity.
Fluroacetic acid > 3-fluropropanoic acid > Iodoacetic acid.
c. p-nitrobenzoic acid > p-methoxybenzoic acid > benzoic acid
Acidity depend upon the ability to lose H+ ion easily. The O-H bond in p-nitrobenzoic acid is weaker because nitro group is electron withdrawing while O-H bonduin p-methoxybenzoic acid is stronger because electron donating nature of methoxy group. Also, the conjugate base of p-nitrobenzoic acid is more stable due to electron withdrawing natue of both -OCH3 and NO2 (-I effect) while conjugate base of p-methoxy benzoic acid is less stable due to electron donating nature of methoxy group.
Therfore p-nitrobenzoic acid > p-methoxybenzoic acid.
In p-nitrobenzoic acid , nitro group has -I effect (el ctron withdrawing nitro group attached to the para position). so it withdraw electron from benzene and stabilize by resonance. But benzoc acid do not have any substitute group and its benzoate ion is less stable than p-nitrobenzoate ion.
Therefore, p-nitrobenzoic acid > p-methoxybenzoic acid > Benzoic acid
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