Predicting Proton NMR Signals For C14H14O2 From Copper Coupling Of 1-bromo-4-methoxybenzene And M-cresol

Jul 17, 2025 by ADMIN 105 views

Unveiling the Proton NMR Spectrum of a Copper-Coupled Compound C14H14O2

Introduction

In the fascinating realm of organic chemistry, organic compound synthesis stands as a cornerstone, enabling the creation of complex molecules with tailored properties. Among the myriad of reactions available to synthetic chemists, copper-promoted coupling reactions have emerged as powerful tools for forging carbon-carbon and carbon-heteroatom bonds. These reactions, often characterized by their versatility and efficiency, play a crucial role in the construction of diverse molecular architectures, including pharmaceuticals, agrochemicals, and materials science compounds. In this article, we delve into the synthesis of an organic compound with the molecular formula C14H14O2 achieved through a copper-promoted coupling reaction involving 1-bromo-4-methoxybenzene and m-cresol. Our primary focus will be on predicting the number of unique signals expected in the proton Nuclear Magnetic Resonance (¹H NMR) spectrum of the resulting product, assuming the NMR solvent is a 1:1 mixture of deuterated chloroform (CDCl3) and deuterated dimethyl sulfoxide (DMSO-d6). Understanding ¹H NMR spectroscopy is essential for elucidating the structure and dynamics of organic molecules. This spectroscopic technique provides valuable information about the number, type, and connectivity of hydrogen atoms within a molecule. By analyzing the chemical shifts, splitting patterns, and integration values observed in a ¹H NMR spectrum, chemists can gain insights into the molecular structure, stereochemistry, and purity of a compound. In the specific case of our synthesized compound C14H14O2, predicting the number of unique signals in the ¹H NMR spectrum requires a careful consideration of the molecular symmetry and the chemical environment of each hydrogen atom. This analysis involves identifying chemically equivalent protons, which will give rise to the same signal, and distinguishing them from non-equivalent protons, which will produce distinct signals. The solvent system used for ¹H NMR spectroscopy can also influence the chemical shifts and signal shapes observed in the spectrum. In this case, a 1:1 mixture of CDCl3 and DMSO-d6 is employed, which can affect the hydrogen bonding interactions and solvation of the compound, potentially altering the chemical shifts of certain protons. By combining our knowledge of organic chemistry principles, ¹H NMR spectroscopy, and the specific reaction conditions, we can accurately predict the number of unique signals expected in the ¹H NMR spectrum of the synthesized compound C14H14O2. This prediction will not only help us confirm the identity of the product but also provide valuable information about its molecular structure and properties.

Synthesis of C14H14O2 via Copper-Promoted Coupling

The synthesis of the target compound, C14H14O2, involves a copper-promoted coupling reaction between 1-bromo-4-methoxybenzene and m-cresol. This type of reaction is a powerful method for forming carbon-carbon bonds, specifically biaryl linkages, which are prevalent in many natural products, pharmaceuticals, and materials. Copper catalysts are particularly attractive due to their relatively low cost, availability, and ability to promote a wide range of coupling reactions. The mechanism of copper-promoted coupling reactions typically involves several steps, including oxidative addition of the aryl halide (1-bromo-4-methoxybenzene) to the copper catalyst, transmetalation with the nucleophile (m-cresol), and reductive elimination to form the coupled product. Ligands play a crucial role in these reactions by modulating the reactivity and selectivity of the copper catalyst. The choice of ligand can significantly influence the reaction outcome, affecting factors such as reaction rate, yield, and regioselectivity. In this specific reaction, 1-bromo-4-methoxybenzene acts as the electrophilic coupling partner, while m-cresol serves as the nucleophilic coupling partner. 1-bromo-4-methoxybenzene is an aromatic compound with a bromine substituent and a methoxy group on the benzene ring. The bromine substituent makes the carbon atom attached to it electrophilic, making it susceptible to nucleophilic attack. The methoxy group is an electron-donating group, which can influence the reactivity and regioselectivity of the coupling reaction. M-cresol, also known as 3-methylphenol, is another aromatic compound with a methyl group and a hydroxyl group attached to the benzene ring. The hydroxyl group is a nucleophilic group, which can attack electrophilic centers. The methyl group can also influence the regioselectivity of the reaction due to steric and electronic effects. The copper-promoted coupling reaction between 1-bromo-4-methoxybenzene and m-cresol results in the formation of a biaryl ether, where the two aromatic rings are connected through an oxygen atom. This type of linkage is commonly found in natural products and biologically active molecules. The reaction is typically carried out under basic conditions, which deprotonate the hydroxyl group of m-cresol, making it a stronger nucleophile. A copper catalyst and a suitable ligand are also required to promote the coupling reaction. The reaction conditions, such as temperature, reaction time, and solvent, can also influence the yield and selectivity of the reaction. Once the coupling reaction is complete, the product, C14H14O2, can be isolated and purified using standard techniques, such as extraction, chromatography, and crystallization. The structure of the product can be confirmed using various spectroscopic methods, including ¹H NMR spectroscopy, which is the focus of our discussion. By analyzing the ¹H NMR spectrum of the product, we can determine the number of unique signals, chemical shifts, and coupling patterns, which provide valuable information about the structure and purity of the compound.

Predicting Unique Signals in the ¹H NMR Spectrum

The prediction of unique signals in the ¹H NMR spectrum of the product C14H14O2 requires a careful analysis of the molecular structure and symmetry. ¹H NMR spectroscopy is a powerful technique that provides information about the number, type, and environment of hydrogen atoms in a molecule. The number of unique signals in the ¹H NMR spectrum corresponds to the number of sets of chemically equivalent protons in the molecule. Chemically equivalent protons are those that are in the same chemical environment and are therefore indistinguishable by NMR spectroscopy. To predict the number of unique signals, we need to identify all the chemically equivalent protons in the molecule. This can be done by considering the symmetry of the molecule and the chemical environment of each proton. Protons that are related by a symmetry operation, such as a rotation or reflection, are chemically equivalent and will give rise to the same signal in the ¹H NMR spectrum. Protons that are in different chemical environments, such as those attached to different atoms or those that are cis or trans to different substituents, are chemically non-equivalent and will give rise to different signals. In the case of C14H14O2, the molecule consists of two aromatic rings connected by an ether linkage. One aromatic ring is substituted with a methoxy group, and the other is substituted with a methyl group. The methoxy group and the methyl group are both electron-donating groups, but they have different electronic and steric effects. The presence of these substituents and the ether linkage affects the chemical environment of the protons in the molecule, leading to different chemical shifts in the ¹H NMR spectrum. To determine the number of unique signals, we need to consider the symmetry of the molecule and the chemical environment of each proton. The molecule does not have any symmetry elements, such as a plane of symmetry or a center of inversion. Therefore, protons that are not related by symmetry are chemically non-equivalent. However, within each aromatic ring, some protons may be chemically equivalent due to free rotation around the carbon-carbon bonds. For example, the two ortho protons on the ring with the methoxy substituent may be chemically equivalent, as are the two meta protons. Similarly, the two ortho protons and the two meta protons on the ring with the methyl substituent may be chemically equivalent within their respective sets. The protons of the methoxy group (-OCH3) are chemically equivalent to each other, as they are all attached to the same carbon atom and are freely rotating. The protons of the methyl group (-CH3) are also chemically equivalent to each other for the same reason. The hydroxyl proton (-OH) on the m-cresol moiety is unique and will give rise to a separate signal in the ¹H NMR spectrum. The chemical shift of this proton is highly dependent on the solvent and concentration due to hydrogen bonding interactions. In a 1:1 mixture of CDCl3 and DMSO-d6, the hydroxyl proton is expected to be significantly broadened due to hydrogen bonding. By carefully considering the symmetry and chemical environment of each proton in C14H14O2, we can predict the number of unique signals expected in the ¹H NMR spectrum. This prediction will help us interpret the experimental ¹H NMR spectrum and confirm the structure of the synthesized compound.

Detailed Analysis of Proton Environments in C14H14O2

To accurately predict the number of unique signals in the ¹H NMR spectrum of C14H14O2, a detailed analysis of the proton environments within the molecule is crucial. This involves identifying all sets of chemically equivalent protons, which will resonate at the same frequency in the NMR spectrum, and distinguishing them from non-equivalent protons, which will give rise to distinct signals. Let's break down the structure of C14H14O2 and examine each proton environment:

Methoxy Group (-OCH3): The three protons of the methoxy group are chemically equivalent due to free rotation around the carbon-oxygen bond. Therefore, they will produce a single, sharp signal in the ¹H NMR spectrum. The chemical shift of these protons is typically observed in the range of 3.7-4.0 ppm, depending on the electronic environment.
Aromatic Ring with Methoxy Substituent: This ring has four protons. Due to the presence of the methoxy group, the aromatic ring is not symmetrical. The two protons ortho to the methoxy group are chemically equivalent, and the two protons meta to the methoxy group are also chemically equivalent. However, the ortho and meta protons are not equivalent to each other. Therefore, we expect to see three signals from this ring: one for the two ortho protons, one for the two meta protons, and one for the para proton. The chemical shifts of these protons will depend on the electronic effects of the methoxy group and the ether linkage.
Aromatic Ring with Methyl Substituent: This ring also has four protons. Similarly, the presence of the methyl group breaks the symmetry of the ring. The two protons ortho to the methyl group are chemically equivalent, and the two protons meta to the methyl group are also chemically equivalent. However, the ortho and meta protons are not equivalent to each other. Therefore, we expect to see three signals from this ring: one for the two ortho protons, one for the two meta protons, and one for the para proton. The chemical shifts of these protons will be influenced by the electronic effects of the methyl group and the ether linkage.
Methyl Group (-CH3): The three protons of the methyl group are chemically equivalent due to free rotation around the carbon-carbon bond. They will produce a single, sharp signal in the ¹H NMR spectrum. The chemical shift of these protons is typically observed in the range of 2.2-2.5 ppm, depending on the electronic environment.
Hydroxyl Proton (-OH): The hydroxyl proton is unique and will give rise to a separate signal in the ¹H NMR spectrum. The chemical shift of this proton is highly variable and depends on factors such as solvent, concentration, and temperature. In protic solvents like DMSO, the hydroxyl proton can form hydrogen bonds, which can broaden the signal and shift its position downfield. In a 1:1 mixture of CDCl3 and DMSO-d6, the hydroxyl proton is expected to be significantly broadened due to hydrogen bonding.

By summing up the number of signals from each proton environment, we can predict the total number of unique signals expected in the ¹H NMR spectrum of C14H14O2. In this case, we expect 1 signal from the methoxy group, 4 signals from the aromatic ring with the methoxy substituent, 4 signals from the aromatic ring with the methyl substituent, 1 signal from the methyl group, and 1 signal from the hydroxyl proton. Therefore, the total number of unique signals expected in the ¹H NMR spectrum of C14H14O2 is 10. This prediction can be further refined by considering the coupling patterns of the aromatic protons, which can provide additional information about the connectivity and stereochemistry of the molecule.

Expected ¹H NMR Spectrum and Signal Multiplicities

Based on the detailed analysis of proton environments in C14H14O2, we can now predict the expected ¹H NMR spectrum, including the number of unique signals, their approximate chemical shifts, and the expected signal multiplicities. This prediction will help us interpret the experimental ¹H NMR spectrum and confirm the structure of the synthesized compound. As determined earlier, we anticipate a total of 10 unique signals in the ¹H NMR spectrum of C14H14O2. Let's discuss each signal in detail:

Methoxy Group (-OCH3): This signal is expected to appear as a singlet in the range of 3.7-4.0 ppm. The three protons are chemically equivalent and do not have any neighboring protons to couple with, resulting in a singlet. The chemical shift is characteristic of methoxy protons attached to an aromatic ring.
Aromatic Ring with Methoxy Substituent: This ring will give rise to four signals due to the non-equivalence of the aromatic protons.
- The two protons ortho to the methoxy group are expected to appear as a doublet of doublets (dd) in the range of 6.8-7.2 ppm. They are coupled to each other (ortho coupling) and to the meta proton on the same ring.
- The two protons meta to the methoxy group are expected to appear as a doublet of doublets (dd) in the range of 7.2-7.5 ppm. They are coupled to each other (meta coupling) and to the ortho proton on the same ring.
- The proton para to both substituents is expected to appear as a triplet in the range of 6.8-7.2 ppm. It is coupled to the two meta protons on the same ring.
Aromatic Ring with Methyl Substituent: Similar to the previous ring, this ring will also give rise to four signals due to the non-equivalence of the aromatic protons.
- The two protons ortho to the methyl group are expected to appear as a doublet of doublets (dd) in the range of 7.0-7.4 ppm. They are coupled to each other (ortho coupling) and to the meta proton on the same ring.
- The two protons meta to the methyl group are expected to appear as a doublet of doublets (dd) in the range of 7.0-7.4 ppm. They are coupled to each other (meta coupling) and to the ortho proton on the same ring.
- The proton para to both substituents is expected to appear as a triplet in the range of 6.8-7.2 ppm. It is coupled to the two meta protons on the same ring.
Methyl Group (-CH3): This signal is expected to appear as a singlet in the range of 2.2-2.5 ppm. The three protons are chemically equivalent and do not have any neighboring protons to couple with, resulting in a singlet.
Hydroxyl Proton (-OH): This signal is expected to appear as a broad singlet in the range of 4.0-6.0 ppm. The chemical shift and broadening are due to hydrogen bonding interactions with the solvent. The broadness of the signal is a characteristic feature of hydroxyl protons in ¹H NMR spectra.

The predicted ¹H NMR spectrum provides a valuable tool for confirming the structure of the synthesized compound C14H14O2. By comparing the experimental ¹H NMR spectrum with the predicted spectrum, we can verify the presence of the expected signals, their chemical shifts, and multiplicities. Any discrepancies between the predicted and experimental spectra may indicate the presence of impurities or the formation of unexpected products. In addition to confirming the structure of the product, the ¹H NMR spectrum can also provide information about the purity of the compound. The presence of additional signals in the spectrum may indicate the presence of impurities, which can be quantified by integrating the signals. Overall, ¹H NMR spectroscopy is a powerful technique for characterizing organic compounds, and the ability to predict the ¹H NMR spectrum is an essential skill for any organic chemist.

Conclusion

In conclusion, the synthesis of C14H14O2 via a copper-promoted coupling reaction highlights the power of organic synthesis in creating complex molecules. The accurate prediction of unique signals in the ¹H NMR spectrum of the product is a crucial step in confirming its structure and purity. By carefully analyzing the molecular symmetry and the chemical environment of each proton, we determined that 10 unique signals are expected in the ¹H NMR spectrum of C14H14O2. These signals correspond to the methoxy group, the aromatic ring protons (both with methoxy and methyl substituents), the methyl group, and the hydroxyl proton. The predicted chemical shifts and signal multiplicities provide a detailed fingerprint for the compound, which can be compared with experimental data to verify the identity of the synthesized product. This exercise underscores the importance of understanding ¹H NMR spectroscopy and its application in structural elucidation. ¹H NMR spectroscopy is an indispensable tool in organic chemistry, allowing chemists to identify and characterize organic molecules with high precision. The ability to predict ¹H NMR spectra based on molecular structure is a fundamental skill for any organic chemist, enabling them to interpret experimental data and gain insights into the structure, dynamics, and purity of organic compounds. Furthermore, the use of copper-promoted coupling reactions demonstrates the versatility and efficiency of modern synthetic methodologies. These reactions provide a powerful means for forming carbon-carbon bonds, which are essential for constructing complex molecular architectures. As the field of organic chemistry continues to evolve, the development of new and improved synthetic methods, coupled with advanced spectroscopic techniques, will undoubtedly lead to the discovery of novel molecules with fascinating properties and applications. In the context of C14H14O2, the knowledge gained from this analysis can be further applied to study its chemical properties, reactivity, and potential applications in various fields, such as pharmaceuticals, materials science, and agrochemistry. The combination of synthetic chemistry and spectroscopic characterization provides a comprehensive approach to understanding the structure and function of organic molecules, paving the way for future discoveries and innovations.