Treatment of 2 -(4-hydroxyphenyl)ethyl bromide with basic...

Treatment of 2 -(4-hydroxyphenyl)ethyl bromide with basic alumina produces a white solid, $\mathrm{mp}, 40-43^{\circ} \mathrm{C}$; IR $1640 \mathrm{~cm}^{-1}$; UV $_{\max } 282 \mathrm{~nm}$ in $\mathrm{H}_{2} \mathrm{O}$; NMR two singlets of equal intensity at $1.69$ and $6.44 \mathrm{ppm}$ from TMS; anal: C $79.98 \% \mathrm{H}$, $6.71 \%$. Suggest a possible structure for this product and explain how it could be formed.

Key Concepts

Dehydrohalogenation

This is the reaction in which a hydrogen atom and a halogen atom are removed from adjacent carbon atoms in an organohalide, resulting in the formation of a carbon–carbon double bond. It is a common method for converting saturated alkyl halides to unsaturated alkenes under basic conditions. In many cases, a solid base or adsorbent such as basic alumina can be used to promote such eliminations.

Elimination Mechanisms (E2/E1)

Elimination reactions proceed via mechanisms in which a proton and a leaving group depart simultaneously (E2) or in a step?wise manner involving a carbocation intermediate (E1). The choice of mechanism depends on the substrate structure, the base used and the reaction conditions. In heterogeneous systems like reactions on basic alumina, the surface can mediate the deprotonation and loss of the leaving group to form a double bond.

Reactions on Basic Solid Supports

Solid supports such as basic alumina can serve as catalysts and mild bases to induce transformations such as dehydrohalogenation. Their surfaces can help adsorb reactants, stabilize charged intermediates, and promote bond cleavage under relatively neutral and anhydrous conditions. This approach is useful for eliminating unwanted side?reactions and for achieving a selective transformation.

Vinylphenol Structural Motif

Vinylphenols are compounds in which a phenolic ring is substituted by a vinyl group (–CH=CH2). They are an important class of compounds in organic chemistry and are characterized by their conjugated structure, which gives rise to distinctive UV absorption and IR C=C stretching frequencies. Their formation often results from the elimination of HX from hydroxyphenylethyl compounds.

Spectroscopic Characterization in Organic Structure Determination

The use of multiple spectroscopic techniques—such as melting point determination, infrared spectroscopy, ultraviolet spectroscopy, nuclear magnetic resonance spectroscopy and elemental analysis—is essential to determine the structure of an unknown organic product. Each technique provides complementary information about functional groups, degree of unsaturation, symmetry and molecular connectivity that allows for the construction of a plausible structure based on the experimental data.

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