Which prefix denotes a hydrocarbon with two carbon atoms?

Which prefix denotes a hydrocarbon with two carbon atoms?

• A. Eth
• B. Prop
• C. But
• D. Pent

Answer: (A)

In hydrocarbon naming, prefixes indicate how many carbon atoms are in the molecule. The sequence goes meth- for one carbon, eth- for two, prop- for three, but- for four, pent- for five, and so on. Since two carbon atoms are involved, the correct prefix is eth-. That’s why the two-carbon hydrocarbon is called ethane, and related two-carbon compounds like ethene and ethyne also start with eth-. The other prefixes correspond to longer carbon chains (three, four, five, etc.), so they don’t describe a two-carbon hydrocarbon.

In hydrocarbon naming, prefixes indicate how many carbon atoms are in the molecule. The sequence goes meth- for one carbon, eth- for two, prop- for three, but- for four, pent- for five, and so on. Since two carbon atoms are involved, the correct prefix is eth-. That’s why the two-carbon hydrocarbon is called ethane, and related two-carbon compounds like ethene and ethyne also start with eth-. The other prefixes correspond to longer carbon chains (three, four, five, etc.), so they don’t describe a two-carbon hydrocarbon.