Question

Which is dehydrated to a maximum extent using conc. \(\mathrm{H}_{2} \mathrm{SO}_{4}\) ? (a) O=C1CCCCC1O (b) O=C1CCC(O)CC1 (c) O=C1CCCC(O)C1 (d) CC1C(=O)CCCC1O

Short answer

Compound (c) is dehydrated to a maximum extent.

Step-by-step solution

Identify Functional Groups

Analyze the given molecular structures to identify functional groups. Each compound contains a hydroxyl (\(-OH\)) group attached to a cyclohexanone ring, which allows for possible dehydration reactions in an acidic medium.

Recognize Dehydration Potential

Dehydration is the removal of a water molecule. Concentrated \(\mathrm{H}_2\mathrm{SO}_4\) is a strong dehydrating agent, which facilitates this process. The position of the hydroxyl group with respect to the carbonyl group affects the dehydration reaction efficiency.

Analyze Compound (a)

Compound (a) is cyclohexanone with an \(-OH\) group at the carbon directly attached to the carbonyl carbon. This \(\beta\)-position promotes a stable enol form but limits extended conjugation during dehydration.

Analyze Compound (b)

Compound (b) is similar to (a) with an \(-OH\) group at a different position. However, this does not significantly differ in terms of dehydration potential compared to compound (a).

Analyze Compound (c)

Compound (c) features a \(\beta\)-hydroxy ketone arrangement, allowing dehydration to form conjugated enones. This \(\beta\)-hydroxyl position offers higher potential for dehydration, creating a more stable product.

Analyze Compound (d)

Compound (d) has an additional alkyl group attached to the cyclohexanone ring, enabling the formation of stable conjugated systems upon dehydration. However, its proximity may reduce effectiveness compared to the diol structure in compound (c).

Determine Maximum Dehydration

Compound (c), being a \(\beta\)-hydroxy ketone, is best positioned for dehydration. The extended stability conferred by conjugation in the resulting enone structure maximizes dehydration extent, more than any of the other options.

Key concepts

Hydroxyl Group

The hydroxyl group is a fundamental functional group in chemistry, consisting of an oxygen atom bonded to a hydrogen atom, written as ( -OH ). This group is polar, meaning it has a slight electrical dipole moment due to the uneven distribution of electrons, with oxygen being more electronegative than hydrogen. This polarity allows hydroxyl groups to engage in hydrogen bonding, significantly influencing the compounds' properties, such as boiling and melting points. The presence of a hydroxyl group in a compound such as alcohols or phenols makes them readily reactive, often participating in substitution or elimination reactions. When discussing chemical dehydration, particularly in acidic conditions, the hydroxyl group is critical, as it can be easily removed to form a water molecule and a new chemical bond in the resulting product. The removal of the hydroxyl group and an adjacent hydrogen atom represents the essence of dehydration reactions. Use of strong acids like concentrated sulfuric acid facilitates this process, which is a vital step in creating more stable structures, like conjugated enones, from compounds containing hydroxyl groups.

Conjugation in Enones

Conjugation in enones refers to a unique structural feature where single and multiple bonds alternate, allowing electrons to delocalize or spread out over several atoms. This delocalization leads to greater stability of the molecule due to what chemists call resonance stabilization.In the context of chemical dehydration, conjugation plays an essential role because it often results from the dehydration of \(\beta\)-hydroxy ketones inn acidic conditions, like with concentrated sulfuric acid. By removing a hydroxyl group and forming a double bond, the recently formed enone structure benefits from this electron delocalization.Conjugated enones are crucial in chemistry due to their reactiveness and stability, often partaking in synthetic organic reactions. This extra stability and reactivity make them attractive targets, for example, in the synthesis of fine chemicals and pharmaceuticals. Conjugation grants enones enhanced properties, such as increased absorption in the UV-visible spectrum, which chemists can exploit to understand their environments and reactions.

Beta-Hydroxy Ketone

A \(\beta\)-hydroxy ketone is a compound characterized by the presence of a hydroxyl group attached to the \(\beta\)-carbon of a ketone.The \(\beta\) position is the second carbon away from a functional group, here specifically referring to the carbonyl (C=O) group. This placement imparts unique properties to the compound, particularly in dehydration reactions. When a \(\beta\)-hydroxy ketone is subjected to an acidic environment, like concentrated sulfuric acid, it undergoes dehydration to lose water and form an α,\(\beta\)-unsaturated ketone, known as an enone.This formation often results in conjugation, leading to a more stable enone structure than was possible before. The stability and reactivity of such structures find utility in many synthesis contexts, including in fine chemicals and pharmaceuticals. Understanding these transformations is crucial, as \(\beta\)-hydroxy ketones serve as versatile building blocks in organic chemistry, capable of further complex reactions through various pathways.

Concentrated Sulfuric Acid

Concentrated sulfuric acid (\(\text{H}_2 ext{SO}_4\)) is one of the most powerful dehydrating agents available in chemistry. With its strong affinity for water, it not only acts as an acid but also removes water molecules from compounds, driving crucial dehydration reactions forward.When used in reaction with \(\beta\)-hydroxy ketones, concentrated sulfuric acid efficiently strives to eliminate water, even overcoming relatively stable molecular configurations. This dehydration is more efficient in such environments due to the acid's additional function of protonating the hydroxyl group, making it a better leaving group.Beyond dehydration, concentrated sulfuric acid finds use in numerous chemical processes due to its ability to sulfonate, hence adding sulfonyl groups to organic compounds, as well as its efficacy in various esterification reactions. Handling sulfuric acid requires care due to its highly corrosive nature and potential to cause severe burns. Hence, it is primarily utilized in well-controlled laboratory settings, warranting proper safety precautions.

Functional Groups in Chemistry

Functional groups are specific groupings of atoms within molecules that have distinct characteristic properties and reactivity, irrespective of the molecule they are part of. They determine how a molecule will react, behave, and interact with other chemicals. Functional groups serve as the cornerstone of understanding chemical behavior and synthesis in organic chemistry, allowing chemists to predict the reactivity and properties of organic molecules.Common functional groups you might encounter include hydroxyl (\(-OH\)), carbonyl (\(C=O\)), amino (\(-NH_2\)), and carboxyl (\(-COOH\)). The role of a functional group is crucial because they often dictate the chemical reactivity of a molecule and can participate in various chemical reactions, including oxidation-reduction, acid-base, and substitution reactions. Understanding functional groups is particularly important in designing synthetic pathways and predicting the outcomes of chemical reactions. For instance, knowing that a hydroxyl group can be dehydrated under acidic conditions is essential when planning to synthesize a particular type of compound. Thus, functional groups can be seen as the critical alphabet of chemical reactivity and synthesis, enabling the vast tapestry of chemical reactions and products we see.