Which of the following compounds is unsaturated?

Analyze the question: An unsaturated compound contains at least one carbon-carbon double or triple bond (C=C or C≡C). Saturated compounds have only single bonds.

Concept: Alkanes, cycloalkanes, ethers and haloalkanes made only of single bonds are saturated. Alkenes (suffix -ene) and alkynes (suffix -yne) are unsaturated.

Check each option:

• A. Cyclohexane (C₆H₁₂): A ring of single bonds only. It is saturated, even though its formula looks like an alkene's (CₙH₂ₙ). It has a ring instead of a double bond.
• B. Methoxyethane (CH₃-O-CH₂CH₃): An ether with only single bonds. Saturated.
• C. 1,2-dibromoethane (BrCH₂-CH₂Br): This is ethane with two Br atoms. All bonds are single, so it is saturated.
• D. 2,2,3-trimethylpentane: A branched alkane, all single bonds. Saturated.
• E. 3-methylbut-1-ene (CH₂=CH-CH(CH₃)-CH₃): The "-1-ene" shows a C=C double bond between carbons 1 and 2. This is unsaturated.

Answer: E, 3-methylbut-1-ene.

Tip: Look at the name's ending. "-ane" means saturated, while "-ene" or "-yne" means unsaturated. Be careful with cyclohexane. It has the alkene formula CₙH₂ₙ but is saturated, because a ring uses up the hydrogens instead of a double bond.