Question

Draw structures of the following derivatives. (i) The \(2.4\) -dinitrophenylhydrazone of benzaldehyde (ii) Cyclopropanone oxime (iii) Acetaldehydedimethylacetal (iv) The semicarbazone of cyclobutanone (v) The ethylene ketal of hexan-3-one (vi) The methyl hemiacetal of formaldehyde

Short answer

Draw each derivative by modifying the parent structure as described in each step.

Step-by-step solution

Understand the derivatives

Each compound mentioned is a derivative of a given organic compound. Understanding the specific reaction or structural modification described is crucial to drawing the correct structure.

Draw benzaldehyde and its 2,4-dinitrophenylhydrazone

Start by drawing benzaldehyde, which is a benzene ring with a formyl group (-CHO). For the 2,4-dinitrophenylhydrazone, a 2,4-DNP group reacts with the aldehyde, replacing the oxygen with the dinitrophenylhydrazine group. Draw the benzene ring and attach the dinitrophenylhydrazone group to it.

Draw the structure of cyclopropanone oxime

Cyclopropanone is a triangular structure (three carbon atoms forming a ring) with a C=O group. The oxime derivative replaces the oxygen in C=O with a nitrogen, creating a double bond to form C=N-OH from the carbonyl group.

Draw acetaldehydedimethylacetal

Acetaldehyde, CH₃CHO, when reacted as a dimethylacetal forms CH₃CH(OCH₃)₂. This is done by replacing the hydrogen atoms of the hydroxyl group with two methoxy groups (-OCH₃).

Draw the semicarbazone of cyclobutanone

Start with cyclobutanone: a four-carbon ring with one carbonyl (C=O) group. Replace the oxygen with a semicarbazone group (-NH2-NH-C(=O)NH2). Attach this to the carbon where the oxygen was replaced.

Draw the ethylene ketal of hexan-3-one

Hexan-3-one has a six-carbon chain with a ketone functional group on the third carbon. The ethylene ketal involves reacting with ethylene glycol, replacing the ketone oxygen and connecting to the two carbons of ethylene glycol.

Draw the methyl hemiacetal of formaldehyde

Formalhyde has the structure HCHO. The methyl hemiacetal involves adding a methanol (CH₃OH) group, forming HCOCH₃(OH) by adding a methanol group across the former C=O bond.

Key concepts

2,4-Dinitrophenylhydrazone

The concept of 2,4-dinitrophenylhydrazone highlights an important derivative in organic chemistry used primarily to identify aldehydes and ketones. By reacting with 2,4-dinitrophenylhydrazine (DNPH), a distinctive and brightly-colored compound is formed.
This structural transformation is quite useful because it provides a way to visibly confirm the presence of carbonyl compounds. During this reaction, the carbonyl oxygen in aldehydes or ketones is effectively replaced with a hydrazone group (-C=N-NH-), linking to the benzene ring of the DNPH.

• Initially, the DNPH attacks the carbonyl carbon.
• Subsequently, the oxygen is replaced with the hydrazone linkage.
• The final product is a stable, crystalline compound.

This derivative not only serves as a method of confirmation but also aids in the purification of the carbonyl compounds due to its solid state.

Cyclopropanone Oxime

Cyclopropanone oxime is created by forming an oxime from cyclopropanone, a molecule characterized by its triangular carbon ring and carbonyl group. Oximes are formed when a ketone or aldehyde reacts with hydroxylamine (NH₂OH). In this case, the action centers around the conversion of the carbonyl group.
When preparing a cyclopropanone oxime:

• The =O of the cyclopropanone is substituted with a =N-OH grouping.
• The oxime formation stabilizes the otherwise reactive cyclopropanone.

This transformation is useful in altering the reactivity of carbonyl groups, allowing further derivatization or reaction control in synthesis procedures.

Acetals and Hemiacetals

Acetals and hemiacetals are types of derivatives formed through the reaction between alcohols and aldehydes or ketones.
Hemiacetals form when one molecule of alcohol adds to an aldehyde or ketone, resulting in a structure containing both an alcohol (-OH) and ether (-OR) group. Acetals are formed when this compound reacts with another alcohol molecule to add a second -OR group, replacing the -OH.

• Acetals: More stable, used in protecting carbonyl groups.
• Hemiacetals: Intermediary, useful in carbohydrate chemistry.

The stability and distinct properties of acetals and hemiacetals make them critical tools in organic synthesis, especially in protecting reactive carbonyl groups during multi-step synthesis.

Semicarbazone

Semicarbazones are a class of Schiff bases derived from aldehydes or ketones by reacting with semicarbazide. This reaction is crucial for the stabilization of carbonyl compounds against oxidation and is also applicable in structural identifications.
In forming a semicarbazone:

• The carbonyl group's oxygen is substituted with a nitrogen-containing group, -NH-C(=O)NH₂.
• This structure results in a stable crystalline form, aiding in purification.

Semicarbazones are particularly valued in the identification of aldehydes and ketones because their crystalline nature leads to easier handling and analysis during chemical experiments.

Ethylene Ketals

Ethylene ketals are formed through the reaction between a ketone and ethylene glycol, often employed for protecting carbonyls in synthetic chemistry. This strategy effectively converts a potentially reactive carbonyl group to a more inert ketal.
The formation process involves:

• The replacement of the carbonyl oxygen with an ethylene glycol-derived structure, creating a 1,3-dioxolane ring.
• Providing a two-point attachment that significantly stabilizes the carbonyl's location.

The protective role of ethylene ketals shields the carbonyl during other reactions, permitting complex syntheses without unintended reactions involving this normally reactive group.