Question

What is the number of moles of tertiary carbon atoms in a molecule of isobutane?

• A. One
• B. Two
• C. Three
• D. Four

Hint:

Chemistry Tip: Visualizing the "T" or "cross" shape of the carbon skeleton helps quickly identify branching. Iso-alkanes always feature one tertiary carbon atom at the end of the chain.

Answer 1

The Correct Option is A

Concept: Chemistry (Organic Chemistry) - Classification of Carbon Atoms.

Step 1: Define the classification of carbon atoms. Carbon atoms in organic molecules are classified based on the number of other carbon atoms directly attached to them: - Primary ($1^\circ$): Attached to one other carbon. - Secondary ($2^\circ$): Attached to two other carbons. - Tertiary ($3^\circ$): Attached to three other carbons. - Quaternary ($4^\circ$): Attached to four other carbons.

Step 2: Determine the structure of isobutane. Isobutane is the common name for 2-methylpropane. Its chemical formula is $C_4H_{10}$. The structural arrangement consists of a central carbon atom bonded to three methyl ($-CH_3$) groups and one hydrogen atom.

Step 3: Analyze the central carbon atom. The central carbon atom in isobutane is directly bonded to three other carbon atoms (the carbons of the three methyl groups). According to the definitions in Step 1, this specific carbon is a tertiary ($3^\circ$) carbon atom.

Step 4: Analyze the terminal carbon atoms. The three methyl carbon atoms are each bonded to only one other carbon (the central one). Therefore, these three are all primary ($1^\circ$) carbon atoms.

Step 5: Count the tertiary carbons and conclude. In a single molecule of isobutane, there is exactly one central carbon atom that fits the tertiary classification. Consequently, in one mole of isobutane molecules, there is exactly one mole of tertiary carbon atoms. $$ \therefore \text{The number of moles of tertiary carbon atoms is One.} $$