Question

Draw the structures of organic compounds A and B. Indicate stereochemistry where applicable.

Answer 1

Concepts and reason

oThe organic reaction involves the transformation of one functional group to another functional group in substrates, using a wide range of reagents at particular conditions.

oAlkynes are unsaturated compounds that contain carbon-carbon triple bonds which will undergo addition reactions.

oAlkenes are unsaturated compounds that contain carbon-carbon double bonds which will undergo electrophilic addition reactions. In electrophilic addition reactions, the weaker pi bonding electrons attack an electrophile, forming a carbocation intermediate, and then a nucleophile attacks the carbocation to form the addition product.

oA reaction is a nucleophilic substitution reaction where the rate of the reaction depends on the two substrates; that is, a nucleophile as well as an alkyl halide. In this reaction, the nucleophile replaces the halide ion in the substrate.

Fundamentals

• Unsaturated hydrocarbons such as alkenes and alkynes undergo hydrogenation reactions on reaction with in the presence of a metal catalyst and result in the formation of new bonds.

• The stereochemistry of hydrogen addition on an alkyne depends on the i) Nature of metals used ii) Reaction conditions (reagents, concentration and temperature).

• A reaction mainly depends on the leaving group ability of the nucleophiles; that is, a halide ion should be a better leaving group than an incoming nucleophile.

• The product formed in a reaction is an inversion at the stereo center to the substrate because the incoming nucleophile attacks from the backside of the leaving group.

• reaction rates depend on both the reactant as well as the product.

• The hydration of alkenes to form alcohols is done with the help of an acid (most commonly, sulfuric acid), a catalyst (most likely, mercury salt), and water as a solvent.

• Lindlar’s catalyst is used to reduce the carbon-carbon triple bonds that exist in the alkynes giving the alkenes.

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