Give the structures of the two stereoisomeric alkenes with...

Give the structures of the two stereoisomeric alkenes with the molecular formula $\mathrm{C}_{6} \mathrm{H}_{12}$ that react with HI to give the same single product and undergo catalytic hydrogenation to give hexane.

Key Concepts

Molecular Structure Identification from Formula

Understanding a compound's molecular formula, like C6H12, involves calculating its degrees of unsaturation to determine the number of rings and pi bonds present. For C6H12, the formula indicates one degree of unsaturation, which is consistent with the presence of one double bond (as in an alkene). Recognizing this helps in deducing the possible structural and stereochemical forms of the molecule, which aligns with the problem of determining stereoisomeric alkenes.

Catalytic Hydrogenation

Catalytic hydrogenation is a type of addition reaction where hydrogen (H2) is added across the double bond of an alkene in the presence of a metal catalyst, such as platinum or palladium. This reaction fully saturates the alkene, converting it into an alkane (in this case, hexane). The process is stereospecific in that it removes the geometry of the original double bond, thereby erasing any original stereochemical differences between isomers.

Electrophilic Addition Mechanism

The electrophilic addition mechanism is a fundamental reaction pathway for alkenes reacting with reagents like hydrogen iodide (HI). In this process, the pi bond of the alkene acts as a nucleophile and attacks the electrophilic hydrogen of HI. This typically follows Markovnikov's rule, where the hydrogen atom adds to the carbon with more hydrogens, forming a carbocation intermediate that subsequently reacts with the iodide ion. This mechanism is key to understanding why both stereoisomeric alkenes can yield the same product upon reaction with HI.

Stereoisomerism

Stereoisomerism refers to the phenomenon where molecules have the same molecular formula and connectivity of atoms but differ in the spatial arrangement of these atoms. In alkenes, this is often observed as cis–trans (or E–Z) isomerism, which plays a crucial role in determining the physical and sometimes chemical properties of the compounds. This concept explains how two molecules with the formula C6H12 can be different yet give the same reaction outcome under certain conditions.

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