For each of the following compounds, how many primary carbons are present? (A) $C_2{H}_6$ (ethane), (B) $C_3{H}_8$ (propane), (C) $C_2{H}_5\mathrm{OH}$ (ethanol)

• A. (A) $1$, (B) $1$, (C) $1$
• B. (A) $2$, (B) $2$, (C) $1$
• C. (A) $2$, (B) $2$, (C) $2$
• D. (A) $1$, (B) $2$, (C) $2$

Answer: (C)

Verified step by step guidance

1. Recall that a primary carbon is a carbon atom bonded to only one other carbon atom. In other words, it is at the end of a carbon chain.
2. For ethane (C\_2H\_6), draw the structure: two carbon atoms single bonded to each other, each carbon bonded to three hydrogens. Both carbons are bonded to only one other carbon, so both are primary carbons.
3. For propane (C\_3H\_8), draw the structure: a chain of three carbons. The two end carbons are each bonded to only one other carbon, so these two are primary carbons. The middle carbon is bonded to two carbons, so it is not primary.
4. For ethanol (C\_2H\_5OH), draw the structure: two carbons with an OH group attached to one of them. The carbon bonded to the OH is also bonded to only one other carbon, making it a primary carbon. The other carbon is bonded to two carbons (one carbon and the OH group is not a carbon), so check carefully: since the OH is not a carbon, the carbon bonded to the OH and one other carbon is primary. The other carbon is bonded to only one carbon (the first carbon), so it is also primary.
5. Count the number of primary carbons in each molecule based on the above analysis to determine the correct answer.