1. Below are the IR and 1H NMR spectra for a compound with the molecular formula of C11H16O. List all the possible information coming from each spectra, and then use this to elucidate the structure from the possible compounds shown. Briefly explain your rationale.
IR spectra:
1H NMR:
1. (Cont’d)
Molecular formula information (i.e., degrees of saturation):
Infrared Spectrum information:
1H-NMR information:
Possible structures:
2. Benzocaine (ethyl p-aminobenzoate) is a local anesthetic that can be prepared by direct esterification of p-aminobenzoic acid with ethanol. (remember that you carried out esterification in the experiment involving the synthesis of aspirin, although you used an anhydride to do so). Using a sulfuric acid as a catalyst (i.e.-acidic conditions), write the detailed mechanism for this reaction.
3. Refer back to the synthesis of aspirin to answer the following questions:
a.) If you used 5.0 g of salicyclic acid and excess acetic anhydride, what would be the theoretical yield of acetylsalicyclic acid in moles? In grams?
b.) A student performed the reaction in this experiment using a water bath at 90°C instead of 50°C. The final product was tested for the presence of phenols with ferric chloride. This test was negative, i.e., no change in color was observed. However, the melting point of the dry product was found to be 122-125°C. Explain these results as completely as possible.
4. Refer back to the Grignard reaction to answer the following questions:
a.) Benzene is often produced as a side-product during Grignard reactions using phenylmagnesium bromide. How can its formation be explained? Give a balanced equation and full mechanism for its formation.
b.) Provide methods for preparing the following compounds by the Grignard method. Identify the starting material for preparing the Grignard reagent, and the reactant it must react with in order to produce the target compound.
5. Refer back to the aldol condensation experiment to answer the following questions:
a.) Give a mechanism for product expected from the reaction of p-anisaldehyde with acetophenone.
b.) How might self-condensation of acetophenone ( which would lead to a nuisance by-product ) be minimized during the synthesis of the above product?
c.) What starting materials would you use to prepare the following compound?
1. Possible structures: In order to determine the structure of the compound based on the given IR and 1H NMR spectra, we need to analyze the information provided in each spectrum.
IR spectra: The IR spectrum provides information about the functional groups present in the compound. By analyzing the peaks in the spectrum, we can identify the presence of certain functional groups, such as carbonyl groups (C=O), hydroxyl groups (O-H), and aromatic compounds (C-H stretching).
1H NMR: The 1H NMR spectrum provides information about the hydrogen atoms in the compound. By analyzing the chemical shifts, splitting patterns, and integration values, we can determine the number and types of hydrogen atoms present in the compound.
Molecular formula information: The molecular formula provides information about the number of carbon, hydrogen, and oxygen atoms in the compound. By comparing the molecular formula with the structural possibilities, we can determine the degree of unsaturation (double bonds or rings) in the compound.
Based on the information from the spectra and the molecular formula, we can narrow down the possible structures by considering the functional groups present in the IR spectrum and the number and types of hydrogen atoms present in the 1H NMR spectrum. Then we can eliminate structures that do not match the degree of unsaturation indicated by the molecular formula.
1. To elucidate the structure from the IR and 1H NMR spectra, we need to analyze the information obtained from each spectrum.
IR spectra:
- The IR spectrum provides information about the functional groups present in the compound. The absorption peaks can indicate the presence of specific groups such as carbonyl (C=O), hydroxyl (OH), amine (NH), etc.
1H NMR:
- The 1H NMR spectrum provides information about the hydrogen atoms in the compound. It shows the chemical shift values (typically in ppm) and the integration (relative signal intensity) of the different protons.
- From the 1H NMR spectrum, we can determine the number of unique proton environments, the types of neighboring protons (splitting patterns), and the integration ratio of the protons.
Possible structures:
- Based on the molecular formula C11H16O, we can list possible compounds that match this formula. For example, we can have isomers of alcohols, ethers, aldehydes, ketones, or carboxylic acids.
To determine the structure, we need to compare the information obtained from the spectra with the possible compounds. For example, if the IR spectrum shows a strong absorption peak at around 3300 cm-1, it indicates the presence of an alcohol or carboxylic acid functional group. We can then check if any of the possible compounds have this functional group. The same approach can be applied to the information obtained from the 1H NMR spectrum.
2. The detailed mechanism for the direct esterification of p-aminobenzoic acid with ethanol under acidic conditions (catalyzed by sulfuric acid) is not provided in the question. However, generally, the mechanism involves the protonation of the carboxylic acid group, nucleophilic attack of the alcohol on the carbonyl carbon, and subsequent proton transfer and elimination to form the ester product.
3. a) To determine the theoretical yield of acetylsalicylic acid, we need to calculate the moles of salicylic acid and then convert it to grams.
- Given salicylic acid: 5.0 g
- Molecular weight of salicylic acid: 138.12 g/mol
- Moles of salicylic acid = Mass / Molecular weight = 5.0 g / 138.12 g/mol
- Theoretical yield of acetylsalicylic acid in moles = Moles of salicylic acid
To convert the theoretical yield to grams, we multiply the moles by the molecular weight of acetylsalicylic acid.
b) The fact that the ferric chloride test for phenols was negative suggests that the product obtained did not contain any phenolic groups. This indicates that the reaction did not convert the salicylic acid into acetylsalicylic acid as intended. However, the melting point of the product, which falls within the expected range for acetylsalicylic acid, suggests that a similar compound was formed. It is possible that the reaction conditions may have caused some side reactions or incomplete conversion, leading to a different compound with similar properties.
4. a) The formation of benzene as a side-product during Grignard reactions using phenylmagnesium bromide can be explained by the reaction between water and the Grignard reagent. Phenylmagnesium bromide reacts with water to generate phenol, which then undergoes dehydration to form benzene.
Balanced equation:
Phenylmagnesium bromide + H2O -> Phenol + Magnesium bromide
Phenol -> Benzene + H2O
Mechanism:
1. Phenylmagnesium bromide reacts with water to form phenol and magnesium bromide.
2. Phenol loses a water molecule through dehydration to form benzene.
b) Methods for preparing compounds by the Grignard method:
- Determine the desired target compound and identify the functional group(s) that need to be incorporated.
- Choose a suitable starting material (organic halide or carbonyl compound) to prepare the corresponding Grignard reagent.
- React the Grignard reagent with the desired reactant (another carbonyl compound, for example) to produce the target compound.
5. a) The mechanism for the reaction of p-anisaldehyde with acetophenone in an aldol condensation can involve the following steps:
1. Deprotonation of acetophenone by a base to form an enolate ion.
2. The enolate ion acts as a nucleophile and attacks the carbonyl carbon of p-anisaldehyde.
3. Formation of a tetrahedral intermediate.
4. Rearrangement of the intermediate to yield the desired aldol product.
5. Protonation of the aldol product to give the final compound.
b) To minimize the self-condensation of acetophenone during the aldol condensation synthesis, there are a few methods that can be employed:
- Use a stronger base to favor the deprotonation of the carbonyl compound instead of self-condensation.
- Control the reaction conditions, such as temperature and reaction time, to minimize self-condensation.
- Adjust the reaction stoichiometry by using excess acetophenone or a limiting amount of the carbonyl compound to shift the equilibrium towards the desired product.
c) The starting materials to prepare the desired compound would depend on the specific compound given. Please provide the name or structure of the compound for a more specific answer.