Question

Which of the following does not exist?
I. HO$_2$S—S—SO$_3$H II. HO—SO$_3$—OH
III. HS—S—SH IV. HS—SO$_3$—OH

• A. Only II
• B. Only III
• C. II and IV
• D. I, III and IV

Hint:

Check valency and oxidation state to verify existence of oxyacids.

Answer 1

The Correct Option is C

To determine which compounds do not exist, we need to analyze the structures of each given molecule and evaluate their chemical stability.

1. Compound I: HO$_2$S—S—SO$_3$H
   This compound is called Peroxydisulfuric acid, also known as Marshall's acid. It has the structure of a peroxide linkage (\(-S-S-\)), and such compounds are known. Therefore, this compound can exist.
2. Compound II: HO—SO$_3$—OH
   This compound suggests the structure of an acid with two hydroxyl groups attached directly to a sulfur atom with an SO₃ group. Normally, the hydrogen in the \(-OH\) group on sulfur is not stable due to steric and electronic effects. Such a form doesn't exist independently in a stable manner.
3. Compound III: HS—S—SH
   This structure is similar to a disulfide linkage with terminal sulfhydryl groups, which is a known structure called Disulfane, \(H_2S_2\). This compound is known to exist.
4. Compound IV: HS—SO$_3$—OH
   This compound suggests a combination where hydrogen bound to sulfur and an oxidized sulfur compound are linked. Typically, such mixed combinations with \(HSO_3\) linked directly to \(SO_3\) don't exist as stable compounds.

From the analysis above, Compound II and Compound IV have structural or electronic reasons that do not support their stable existence. Therefore, the correct answer is Option III: II and IV. While Compounds I and III are known structures, Compounds II and IV are not stable or commonly occurring. This reasoning leads to the conclusion that they do not exist.