GRE Subject Test: Chemistry : Hydrocarbons

Study concepts, example questions & explanations for GRE Subject Test: Chemistry

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Example Questions

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Example Question #11 : Organic Chemistry

Starting with an alkyne, synthesis of a cis alkene is driven upon addition of which of the following reagents?

Possible Answers:

Correct answer:

Explanation:

Reduction of an alkyne with hydrogen and Lindlar's catalyst will result in a cis alkene. While  is a reducing agent, when added to an alkyne, a trans alkene is formed. Potassium permanganate is an oxidizing agent and thus will not reduce the triple bond. The Grignard reagent is used to add organic substituents onto carbonyls. Addition of one equivalent of chlorine in carbon tetrachloride solvent yields a trans alkene; addition of a second equivalent of chlorine yields a tetrachloro alkane.

Example Question #1 : Lipids

Which of the following molecule is a type of terpene?

Possible Answers:

 because it is derived from a pentene

 because it is derived from an isoprene

 because it is derived from an isoprene

 because it is derived from a pentene

Correct answer:

 because it is derived from an isoprene

Explanation:

Terpenes are special classes of lipids that are derived from isoprene units. An isoprene unit’s molecular formula is ; therefore, terpenes must contain a molecular formula that is derived from a empirical formula.

The molecular formula consists of seven isoprene units ( = ); therefore,  is a type of terpene.

Pentene is an alkene with the molecular formula .  () is derived from pentene units; however, terpenes do not have pentene units.

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