Which compound is an unsaturated hydrocarbon?

Regents Chemistry Exam June 2025 Question 22

22  Which compound is an unsaturated hydrocarbon?

(1) 1-heptanol (3) octane (2) 2-butyne (4) ethanal

Solution:

Table Q on the Reference Table lists all the series of hydrocarbons. An unsaturated hydrocarbon has either a double bond (alkenes) or a triple bond (alkynes). Therefore, we are looking for a name ending in "ene" or "yne". Choice 2 is the correct answer choice because it ends in "yne."

PS: Choice 1 represents an alcohol functional group, choice 3 is an alkane, and choice 4 is an aldehyde.

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