Question

Oxanamide is a mild sedative belonging to a class of molecules called oxanamides. As seen in this retrosynthetic scheme, the source of carbon atoms for the synthesis of oxanamide is butanal. (a) Show reagents and experimental conditions by which oxanamide can be synthesized from butanal. (b) How many chiral centers are there in oxanamide? How many stereoisomers are possible for this compound?

Short answer

Answer: Oxanamide can be synthesized from Butanal through a two-step process involving the conversion of Butanal to an acid chloride followed by the reaction with a primary amine. There are no chiral centers in Oxanamide, and only one stereoisomer is possible for this compound.

Step-by-step solution

Analyzing the structure of Oxanamide and Butanal

First, we need to understand the structure of Oxanamide and Butanal to determine how to synthesize Oxanamide from Butanal. Oxanamide: \(H_{2}N-CO-NH-CH_{2}-CH_{2}-CH_{2}-CH_{2}-CO\) Butanal: \(CH_{3}-CH_{2}-CH_{2}-CHO\)

Synthesizing Oxanamide from Butanal

To synthesize Oxanamide from Butanal, we need to form the amide bonds between nitrogen and carbonyl groups. To achieve this, we can use a two-step process. First, we'll convert Butanal into an acid chloride, and then react it with a primary amine to form Oxanamide. (a) Reagents and experimental conditions for the synthesis of Oxanamide: 1. Conversion of Butanal to the corresponding acid chloride: Reagents: \(P_{4}O_{10}\), SOCl₂ Experimental conditions: Room temperature, dry environment \(CH_{3}-CH_{2}-CH_{2}-CHO \xrightarrow[]{P_{4}O_{10}, SOCl_{2}} CH_{3}-CH_{2}-CH_{2}-COCl\) 2. Reaction of the acid chloride with a primary amine: Reagents: NH₂NH₂ Experimental conditions: Low temperature, a solvent like ether \(CH_{3}-CH_{2}-CH_{2}-COCl + NH_{2}NH_{2} \xrightarrow[]{ether, low\ temperature} H_{2}N-CO-NH-CH_{2}-CH_{2}-CH_{2}-CH_{2}-CO\)

Identifying Chiral Centers and Stereoisomers of Oxanamide

To determine the number of chiral centers in Oxanamide, let's look at the structure: \(H_{2}N-CO-NH-CH_{2}-CH_{2}-CH_{2}-CH_{2}-CO\) In this molecule, there aren't any atoms with four different groups attached to them. Therefore, there are no chiral centers in Oxanamide. (b) The number of chiral centers in Oxanamide is 0, and since there are no chiral centers, only one stereoisomer is possible for this compound.

Key concepts

Amide Bond Formation

The synthesis of oxanamide involves a crucial chemical interaction known as amide bond formation. An amide bond is a type of covalent bond that connects a carbonyl group (C=O) with a nitrogen atom from an amine.

When synthesizing oxanamide from butanal, the first step is to transform butanal into a more reactive form, such as an acid chloride, which is achieved by reacting butanal with reagents like phosphorus pentoxide (\( P_{4}O_{10} \)) and thionyl chloride (SOCl₂). This step is essential for activating the terminal aldehyde group, turning it into a group that can react with amines.

Once the acid chloride is formed, the next step requires the use of hydrazine (\( NH_{2}NH_{2} \)) to introduce nitrogen. The acid chloride readily reacts with hydrazine, yielding oxanamide through the creation of two amide bonds. This reaction typically takes place at a lower temperature and in a suitable solvent, like ether, to facilitate the process and avoid side reactions. This sequence elegantly demonstrates how organic chemists manipulate functional groups to construct complex molecules from simpler ones.

Retrosynthetic Analysis

Retrosynthetic analysis is a strategy employed by chemists to plan the synthesis of complex organic molecules. It involves breaking down the structure of the target molecule into simpler, readily available precursors. By working backward from the product to the starting materials, chemists can identify feasible synthetic pathways.

In the case of oxanamide, retrosynthetic analysis helps in understanding that butanal, a simple four-carbon aldehyde, can serve as a starting point for synthesis. The analysis recognizes the need for forming amide bonds and determines the necessary reactions and reagents to transform butanal into oxanamide.

Using retrosynthetic principles, chemists can deduce that an intermediate species, perhaps an acid chloride, would be a suitable precursor that could react with an amine to form the amide bonds present in oxanamide. This retrosynthetic approach greatly simplifies the complexity of chemical syntheses and assists in the step-by-step breakdown of the process.

Chiral Centers and Stereoisomers

Chiral centers in a molecule are carbon atoms bonded to four different groups, leading to molecules that are nonsuperimposable on their mirror images, much like how the left hand is different from the right hand. These molecules are termed enantiomers and are a type of stereoisomer.

Oxanamide, however, lacks chiral centers, as all the carbon atoms are bonded to either two hydrogen atoms or identical groups. Without chiral centers, oxanamide does not have enantiomers and thus exists as a single stereoisomer. This significantly simplifies the synthesis of oxanamide since there is no need to worry about creating the wrong stereoisomer, a common concern in syntheses dealing with chiral molecules.

The absence of chiral centers in oxanamide underscores the relevance of molecular symmetry in organic chemistry. Analyzing chiral centers allows chemists to predict the number of possible stereoisomers for a given compound, providing insights into the molecule's properties and the strategies required for its synthesis.