Question

For given reaction sequence, If 'P' has molecular formula ' \(\mathrm{C}_{4} \mathrm{H}_{\mathrm{g}} \mathrm{O}\), produces oxime with \(\mathrm{NH}_{2} \mathrm{OH}\) which shows G.l. and cin alvi' produces racemic product on reaction with LAH. \((\mathrm{W}) \stackrel{\mathrm{CH}_{3}-\mathrm{I}}{\longrightarrow} \stackrel{\mathrm{Hg}(\mathrm{OAc})_{2} / \mathrm{H}_{2} \mathrm{O}}{\longrightarrow} \stackrel{\mathrm{NaBH}_{4} / \mathrm{OH}}{\longrightarrow}\left(\mathrm{W}^{\prime}\right)\) The correct statement(s) is/are (A) \((\mathrm{W})\) will give gem dihalide on reaction with \(\mathrm{HCl}\) (excess) (B) \(\left(\mathrm{W}^{\prime}\right)\) does not give red precipitate with ammoniacal \(\mathrm{AgNO}_{3}\) (C) Both (P) and \(\left(\mathrm{W}^{\prime}\right)\) are member of same homologous series (D) (X) will give red precipitate with ammoniacal \(\mathrm{AgNO}_{3}\)

Short answer

The correct statements are (B) and (D). Compound \(\mathrm{P}\) is butanal (CH3CH2CH2CHO), and compound \(\mathrm{W}^\prime\) is a tertiary alcohol (CH3C(OH)(CH3)CH3). In the given reaction sequence, butanal does not give gem dihalide on reaction with excess HCl (A) and both compounds are not members of the same homologous series (C). Tertiary alcohol \(\mathrm{W}^\prime\) does not give red precipitate with ammoniacal \(\mathrm{AgNO}_{3}\) (B), but butanal (W) will give a red precipitate with ammoniacal \(\mathrm{AgNO}_{3}\) (D).

Step-by-step solution

According to the information given, P has a molecular formula of \(\mathrm{C}_{4}\mathrm{H}_{9}\mathrm{O}\) and produces oxime with \(\mathrm{NH}_{2}\mathrm{OH}\), which shows G.L. reaction. This indicates that P has a carbonyl group, and it can be classified either as an aldehyde or a ketone. The molecular formula is \(\mathrm{C}_{4}\mathrm{H}_{9}\mathrm{O}\), we can identify the compound with carbonyl group which is butanal. So, the compound P is butanal with the structure CH3CH2CH2CHO. #Step 2: Analyzing Reaction Sequence (W)#

The given reaction sequence is: $(\mathrm{W}) \stackrel{\mathrm{CH}_{3}-\mathrm{I}}{\longrightarrow} \stackrel{\mathrm{Hg}(\mathrm{OAc})_{2} / \mathrm{H}_{2} \mathrm{O}}{\longrightarrow} \stackrel{\mathrm{NaBH}_{4} / \mathrm{OH}}{\longrightarrow}\left(\mathrm{W}^{\prime}\right)$ Let's discuss the three reactions involved in the transformation of W to W': 1. Reaction with CH3I (Formation of ketone): Butanone - CH3CH2COCH3 2. Reaction with Hg(OAc)2/H2O (oxymercuration-demercuration): Tertiary alcohol - CH3C(OH)(CH3)CH3 3. Reaction with NaBH4/OH (Reduction): Tertiary alcohol - CH3C(OH)(CH3)CH3 (No change in this step) #Step 3: Answering the questions# A) \((\mathrm{W})\) will give gem dihalide on reaction with \(\mathrm{HCl}\) (excess)

Since W is butanal, which is an aldehyde, it cannot give gem dihalide on reaction with excess HCl as it needs to be an alkene and should have a carbon-carbon double bond. So, A) is false. B) \(\left(\mathrm{W}^{\prime}\right)\) does not give red precipitate with ammoniacal \(\mathrm{AgNO}_{3}\)

The given compound W' is CH3C(OH)(CH3)CH3, which is a tertiary alcohol. Tertiary alcohols do not give a red precipitate with ammoniacal \(\mathrm{AgNO}_{3}\) (Tollens' reagent) as it is a test for aldehydes. So, B) is true. C) Both (P) and \(\left(\mathrm{W}^{\prime}\right)\) are members of the same homologous series

Since P is an aldehyde (butanal) and W' is a tertiary alcohol, they are not part of the same homologous series. So, C) is false. D) (X) will give red precipitate with ammoniacal \(\mathrm{AgNO}_{3}\)

There seems to be a typographical error in the question. The compound to be tested should be (W) instead of (X). As W is butanal, which is an aldehyde, it will give a red precipitate with ammoniacal \(\mathrm{AgNO}_{3}\). So, D) is true. Thus, the correct statements are (B) and (D).

Key concepts

Oxymercuration-Demercuration

Oxymercuration-demercuration is a two-step reaction path that converts alkenes into neutral alcohols. In the first phase, oxymercuration, the alkene reacts with mercury(II) acetate (\texttt{Hg(OAc)\(_2\)}) in water, leading to the formation of a mercurinium ion intermediate. This intermediate is then attacked by a water molecule, which adds to the more substituted carbon of the former double bond due to Markovnikov's rule.

In the subsequent step, demercuration, sodium borohydride (\texttt{NaBH\(_4\)}) is used to replace the mercury atom with a hydrogen atom, creating an alcohol while preventing any rearrangement that might occur with a simple hydration reaction. This method ensures that alkenes can be transformed into alcohols with high regioselectivity, favoring the formation of more stable, substituted alcohols. It's particularly useful in syntheses within organic chemistry, especially when intending to keep the stereochemistry of the product intact.

To grasp meaningful insights about oxymercuration-demercuration, it's key to understand electrophilic addition to alkenes and the concept of regioselectivity. Moreover, it's important to recognize the role of mercury(II) acetate as a soft electrophile in facilitating the addition reaction.

Tollens' Reagent

Tollens' reagent is famously known for its ability to identify aldehydes. This reagent is a solution of silver nitrate (\texttt{AgNO\(_3\)}) in ammonia, which, upon reaction with aldehydes, forms a characteristic silver mirror or a gray to black precipitate of silver. Aldehydes are oxidized by Tollens' reagent to carboxylic acids, while the silver(I) ion (\texttt{Ag\(^+\)}) in the reagent is reduced to metallic silver.

The beauty of Tollens' test lies in its specificity. While it does react positively with aldehydes, it does not with ketones, except for alpha-hydroxy ketones which can undergo an isomerization to form an aldehyde. This makes it a valuable tool for confirming the presence of an aldehyde functional group.

For students learning about functional group identification, comprehending the mechanism of Tollens' test can be pivotal. The reagent itself can be unstable and should be freshly prepared for each use, and the test is conducted at ambient conditions, which are convenient for standard laboratory exercises in organic chemistry.

Gem Dihalide

Gem dihalides (or geminal dihalides) are organic compounds where two halogen atoms are bonded to the same carbon atom, creating a 'geminal' (from the Latin 'gemini' meaning twins) arrangement. Gem dihalides can be synthesized typically by the halogenation of alcohols or through the addition of halogens to alkenes bearing a carbonyl group in the proximity, known as the haloform reaction.

With respect to reactivity, gem dihalides are usually more reactive towards nucleophilic substitution reactions due to the presence of two electronegative halogen atoms, which increase the carbon's electrophilic character. For students to fully understand the characteristics and reactions of gem dihalides, it's crucial to delve into the principles of steric hindrance and electronic effects induced by halogen atoms attached to organic moieties. Moreover, gem dihalides' role as intermediates in the synthesis of various compounds underscores their importance in organic synthesis.

NaBH4 Reduction

Sodium borohydride (\texttt{NaBH\(_4\)}) is a versatile reducing agent commonly used in organic chemistry to reduce carbonyl compounds, such as aldehydes and ketones, to their corresponding alcohols. Under standard conditions, \texttt{NaBH\(_4\)} selectively reduces aldehydes and ketones as it's less reactive than its cousin, lithium aluminum hydride (\texttt{LiAlH\(_4\)}), and generally doesn't reduce esters, amides, or carboxylic acids.

This mild nature of \texttt{NaBH\(_4\)} allows chemists to perform chemoselective reductions where functional group compatibility is crucial. Understanding when to use \texttt{NaBH\(_4\)} as opposed to other reducing agents is an essential skill in organic chemistry, as it influences the outcome and efficiency of synthetic pathways. Students should focus on learning the mechanism by which \texttt{NaBH\(_4\)} transfers a hydride ion to the electrophilic carbon in a carbonyl group, resulting in the formation of an alcohol and providing knowledge of fundamental reduction reactions in organic transformation processes.