Give the structure that meets the criteria given in each of...

Give the structure that meets the criteria given in each of the following cases: (a) A compound $\mathrm{C}_{6} \mathrm{H}_{14}$ that gives only two products of monochlorination, one of which is chiral. (b) Four stereoisomeric compounds $\mathrm{C}_{4} \mathrm{H}_{\mathrm{g}} \mathrm{O},$ all optically active, that contain no double bonds and evolve a gas when treated with EtMgBr.

Give the structure that meets the criteria given in each of the following cases:
(a) A compound $\mathrm{C}_{6} \mathrm{H}_{14}$ that gives only two products of monochlorination, one of which is chiral.
(b) Four stereoisomeric compounds $\mathrm{C}_{4} \mathrm{H}_{\mathrm{g}} \mathrm{O},$ all optically active, that contain no double bonds and evolve a gas when treated with EtMgBr.

Key Concepts

Stereoisomerism and Enumerating Stereoisomers

When a molecule contains one or more stereogenic centers, the spatial arrangement of substituents can give rise to multiple stereoisomers. In the case where all stereoisomers are optically active, none are meso, meaning each stereocenter contributes to chirality. This concept is central when determining structures that exhibit exactly four optically active stereoisomers.

Chirality and Optical Activity

The creation of a chiral center in a molecule involves the introduction of a carbon atom bonded to four different substituents. The presence or absence of chirality directly influences the number of stereoisomers (optical isomers) that can result. When a reaction produces a new chiral center, it can lead to enantiomeric pairs which are optically active, a key point in both parts of the problem.

Grignard Reaction Mechanism

This mechanism involves the reaction of organomagnesium reagents with electrophilic centers in compounds. In the context provided, the evolution of a gas upon treatment with EtMgBr suggests that the oxygenated compound contains a functional group (such as a protic –OH) that reacts with the Grignard reagent by deprotonation, releasing a gaseous hydrocarbon. Understanding this interaction helps in deducing structural features of the compound.

Free Radical Substitution and Regioselectivity

This concept deals with how free radical halogenation of alkanes occurs by abstracting hydrogen atoms from different positions. The outcome is governed by the types of C–H bonds (primary, secondary, tertiary) present and the molecular symmetry. In highly symmetric molecules, many equivalent hydrogen atoms lead to fewer distinct products upon substitution because equivalent positions give the same product.

Molecular Symmetry

Molecular symmetry is crucial in determining the number of unique products in substitution reactions. A molecule with high symmetry might have several equivalent hydrogen atoms so that, despite many potential substitution sites, only a few unique products can be formed. In particular, in the example there is a symmetry element that limits the number of distinct chlorinated products to two.

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