Question

A compound with no tertiary hydrogen is (A) \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCH}\left(\mathrm{CH}_{3}\right)_{2}\) (B) \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCH}_{2} \mathrm{CH}_{3}\) (C) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\) (D) \(\left(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}\right)_{4} \mathrm{C}\)

Short answer

The compound with no tertiary hydrogen is (C) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\).

Step-by-step solution

Understand the Molecular Structure of the Given Compounds

Since we have to identify a compound that doesn't contain any tertiary hydrogen i.e., hydrogen joined to a carbon atom which is further attached to three other carbon atoms, we need to understand the structure of each compound. Each compound also has its number of carbon atoms attached to it.

Re-examining Each Option Based on Our Initial Understanding

For (A) \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCH}\left(\mathrm{CH}_{3}\right)_{2}\), you should visualize it as a carbon atom (C) to which five other carbon atoms are attached. This atom will have a hydrogen bonded to it, which makes it a tertiary hydrogen. So, it cannot be our answer. Meanwhile, for (B) \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCH}_{2} \mathrm{CH}_{3}\), there is a carbon atom bonded to three other carbon atoms, making it a tertiary carbon. This tertiary carbon has an attached hydrogen, making it a tertiary hydrogen. Therefore, option B cannot be the answer. Option (C) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\) is quite straightforward. There aren't any tertiary carbon atoms in the molecular structure. So, it should be our answer. However, let's verify option (D) \(\left(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}\right)_{4} \mathrm{C}\) before we conclude. For this molecule, the central carbon is bonded to four other carbons, making it a quaternary carbon. However, on each of these carbons, there is another carbon attached to it, making these tertiary carbons. Thus, option D is ruled out as it contains tertiary hydrogens.

Conclusion

Therefore, after analyzing each given compound, it can be concluded that the answer is (C) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\) because it does not contain any tertiary carbon atoms and hence no tertiary hydrogen.

Key concepts

Molecular Structure

When we talk about molecular structure, we're referring to the specific arrangement of atoms in a molecule. Understanding this structure helps in predicting the properties and behavior of the compound. For example, each carbon atom in a compound can form up to four bonds with other atoms, including carbon and hydrogen. These bonds dictate the structure and type of hydrogens—such as primary, secondary, or tertiary—attached to the carbons.

In the provided exercise, deciphering the molecular structure is crucial to identifying which compound lacks tertiary hydrogens. Tertiary hydrogens are linked to tertiary carbon atoms, which are carbon atoms bonded to three other carbon atoms. This molecular arrangement does not exist in solution (C), making it the correct answer.

Visualizing the molecular structure can be accomplished through practice in drawing out simplified versions of the compound, using line bonds to represent the connections between different atoms. This process will reveal unique structural features like the presence or absence of tertiary hydrogens.

Tertiary Carbon

Tertiary carbon is a term used to describe a carbon atom bonded to three other carbon atoms. It is an integral part of organic chemistry as it influences a molecule's chemical reactivity and physical properties.

Identifying tertiary carbons in a molecule requires examining how carbon atoms are connected in the molecular structure. In options (A), (B), and (D) from the exercise, tertiary carbons are present because you can find three other carbon atoms linked to certain carbon atoms. This means that if hydrogen is also attached to these carbons, they become tertiary hydrogens.

However, option (C) does not contain any tertiary carbons. This absence indicates that no tertiary hydrogens are present, as tertiary hydrogens can only exist if there are tertiary carbons. This makes option (C) devoid of tertiary hydrogen, separating it from options A, B, and D.

Quaternary Carbon

The quaternary carbon is a carbon atom bonded to four other carbon atoms. It signifies a significant branching point in organic molecules, which often affects the compound's stability and boiling point. In the given exercise, compound (D) contains a quaternary carbon. Here, a central carbon atom forms bonds with four other carbons. Such a structure leads to the absence of hydrogen directly linked to the quaternary carbon since all its four bonds are tied to carbon, not hydrogen. Understanding quaternary carbons can help distinguish significant molecular characteristics, such as the absence of certain types of hydrogens. This insight was pivotal in confirming that compound (D) does not meet the criteria of lacking tertiary hydrogens as it supports quaternary carbon structures instead.