21.10 Spectroscopy of Carboxylic Acid Derivatives
3 min read•may 7, 2024
derivatives have unique spectroscopic fingerprints. reveals distinct carbonyl absorptions, while NMR shows characteristic chemical shifts for adjacent hydrogens and carbonyl carbons. These tools help identify and distinguish between different types of carbonyl compounds.
Understanding these spectroscopic patterns is crucial for structural analysis. By combining IR, NMR, and data, chemists can confidently determine the structure of unknown carboxylic acid derivatives and related compounds. This skill is essential for organic synthesis and analysis.
Spectroscopic Analysis of Carboxylic Acid Derivatives
Carbonyl identification through infrared
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- Carbonyl group () has a characteristic IR absorption frequency absorbs in the range of 1650-1850 cm (ketones, aldehydes)
- Exact frequency depends on the type of carbonyl compound influenced by factors such as resonance and electron-withdrawing groups
- These absorptions are due to of the carbonyl bond
- Carboxylic acids absorb around 1700-1725 cm (acetic acid, benzoic acid)
- Also show a broad absorption at 2500-3300 cm due to hydrogen bonding between carboxylic acid molecules
- Esters absorb around 1735-1750 cm (ethyl acetate, methyl benzoate)
- Higher frequency than carboxylic acids due to resonance stabilization of the carbonyl group by the adjacent oxygen atom
- Amides absorb around 1640-1690 cm (acetamide, benzamide)
- Lower frequency than carboxylic acids and esters due to resonance delocalization of the nitrogen lone pair into the carbonyl group
- Anhydrides show two carbonyl absorptions (acetic , phthalic anhydride)
- Symmetric stretch at 1800-1830 cm results from in-phase stretching of the two carbonyl groups
- Asymmetric stretch at 1740-1775 cm results from out-of-phase stretching of the two carbonyl groups
- absorb at higher frequencies (1785-1815 cm) (acetyl chloride, benzoyl chloride)
- Electron-withdrawing effect of the chlorine atom increases the force constant of the carbonyl bond, leading to higher absorption frequency
NMR detection of carbonyl-adjacent hydrogens
- Hydrogens adjacent to carbonyl groups are deshielded by the electron-withdrawing effect of the carbonyl appear at higher chemical shifts compared to regular alkyl hydrogens
- Carboxylic acids (acetic acid, propionic acid)
- Acidic proton appears as a broad singlet at 10-13 ppm due to rapid exchange with trace amounts of water in the solvent
- -hydrogens (next to the carbonyl) appear at 2.0-2.5 ppm
- Esters (ethyl acetate, methyl propionate)
- -hydrogens appear at 2.0-2.5 ppm
- Hydrogens on the alkoxy group appear at 3.7-4.2 ppm
- Amides (acetamide, N-methylbenzamide)
- N-H protons appear as a broad singlet at 5-9 ppm due to hydrogen bonding and exchange with trace amounts of water
- -hydrogens appear at 2.0-2.5 ppm
- Anhydrides and acid chlorides (acetic anhydride, acetyl chloride)
- -hydrogens appear at 2.0-2.5 ppm
- relies on the of atoms to provide structural information
Carbonyl types in 13C NMR
- Carbonyl carbon appears at characteristic chemical shifts depending on the type of compound
- Carboxylic acids (formic acid, benzoic acid)
- Carbonyl carbon appears at 170-185 ppm
- Esters (methyl formate, ethyl benzoate)
- Carbonyl carbon appears at 165-175 ppm
- Alkoxy carbon appears at 50-70 ppm
- Amides (formamide, N,N-dimethylbenzamide)
- Carbonyl carbon appears at 160-180 ppm
- Anhydrides (acetic anhydride, succinic anhydride)
- Carbonyl carbons appear at 160-175 ppm
- Acid chlorides (acetyl chloride, benzoyl chloride)
- Carbonyl carbon appears at 170-185 ppm
Spectroscopic Techniques for Structural Elucidation
- utilizes the to identify functional groups
- Mass spectrometry involves to determine molecular mass and structural features
- NMR and IR spectroscopy are complementary techniques used for in organic compounds
Key Terms to Review (32)
13C NMR: 13C NMR, or Carbon-13 Nuclear Magnetic Resonance, is a spectroscopic technique used to identify and characterize organic compounds by analyzing the magnetic properties of the carbon-13 isotope within a molecule. It provides valuable information about the chemical environment and connectivity of carbon atoms, which is crucial for understanding the structure and properties of organic compounds.
1H NMR: 1H NMR, or proton nuclear magnetic resonance spectroscopy, is a powerful analytical technique used to determine the structure and composition of organic compounds. It provides information about the chemical environment and connectivity of hydrogen atoms within a molecule.
Acid Chloride: An acid chloride, also known as an acyl chloride, is a highly reactive organic compound derived from a carboxylic acid. It contains a carbonyl group (C=O) bonded to a chlorine atom, making it a versatile and important functional group in organic chemistry.
Acid chlorides: Acid chlorides are a class of organic compounds characterized by the presence of a carbonyl group (C=O) bonded to a chlorine atom. They are derived from carboxylic acids by replacing the hydroxyl group (OH) with a chlorine atom.
Amide: An amide is a functional group consisting of a carbonyl group (C=O) linked to a nitrogen atom (N). Amides are important in organic chemistry and play a crucial role in various topics, including functional groups, elimination reactions, alcohol reduction, nitrile chemistry, amide chemistry, and the spectroscopy of carboxylic acid derivatives.
Anhydride: An anhydride is a type of organic compound derived from a carboxylic acid, where two carboxylic acid groups have been dehydrated to form a cyclic structure containing a central oxygen atom. Anhydrides are closely related to carboxylic acid derivatives and are important in the context of spectroscopic analysis of these functional groups.
Carbonyl Stretch: The carbonyl stretch is a characteristic vibrational mode observed in the infrared (IR) spectrum of molecules containing a carbonyl group (C=O). This absorption band provides valuable information about the structure and environment of the carbonyl group, which is a crucial functional group in various organic compounds.
Carboxylic Acid: Carboxylic acids are organic compounds characterized by the presence of a carboxyl functional group (-COOH), which consists of a carbonyl (C=O) and a hydroxyl (-OH) group. They are widely found in nature and play a crucial role in various organic chemistry topics.
Carboxylic acid derivative: Carboxylic acid derivatives are compounds that contain a functional group which is a modified form of the carboxylic acid group (–COOH), where the hydroxyl part (-OH) is replaced by another atom or group of atoms. These derivatives undergo nucleophilic acyl substitution reactions, where an electron-rich nucleophile attacks the carbonyl carbon, leading to the substitution of the leaving group.
Chemical shift: In nuclear magnetic resonance (NMR) spectroscopy, a chemical shift is a measure of the change in the resonant frequency of a nucleus relative to a standard reference. It provides insights into the electronic environment surrounding a nucleus, helping to identify molecular structures.
Chemical Shift: Chemical shift is a fundamental concept in nuclear magnetic resonance (NMR) spectroscopy that describes the position of a signal in the NMR spectrum relative to a reference signal. It provides information about the chemical environment of a nucleus, allowing for the identification and characterization of different functional groups and molecular structures.
COSY: COSY, short for Correlated Spectroscopy, is a two-dimensional nuclear magnetic resonance (NMR) technique used to identify the connectivity between protons (hydrogen atoms) within a molecule. It is a powerful tool for elucidating the structure of organic compounds by providing information about the spatial relationships between different hydrogen atoms.
Coupling constant: The coupling constant (denoted as J) in Nuclear Magnetic Resonance (NMR) spectroscopy is a measure of the interaction strength between neighboring nuclear spins, influencing the splitting pattern in an NMR spectrum. It is expressed in hertz (Hz) and provides information about the spatial relationship and number of bonds separating adjacent atoms.
Coupling Constant: The coupling constant is a measure of the strength of the spin-spin interaction between two nuclei in a molecule, which is observed in nuclear magnetic resonance (NMR) spectroscopy. It describes the magnitude of the splitting patterns seen in NMR spectra, providing valuable information about the structure and connectivity of molecules.
DEPT: DEPT (Distortionless Enhancement by Polarization Transfer) is a 13C NMR spectroscopic technique that enhances the signal intensity of carbon-13 nuclei by transferring polarization from the more abundant and sensitive hydrogen-1 nuclei. This method is particularly useful in the analysis of carboxylic acid derivatives, as it can provide information about the types of carbon environments present in the molecule.
DEPT-NMR: DEPT-NMR (Distortionless Enhancement by Polarization Transfer Nuclear Magnetic Resonance) is a specialized NMR spectroscopy technique used to differentiate between carbon atoms in organic compounds based on the number of hydrogen atoms attached to them. It provides detailed information about the carbon framework of molecules by selectively highlighting CH, CH2, and CH3 groups.
Deuterated Chloroform: Deuterated chloroform, also known as chloroform-d, is a deuterated version of the common organic solvent chloroform. It is widely used in nuclear magnetic resonance (NMR) spectroscopy as a solvent and reference compound, providing valuable insights into the chemical shifts and proton equivalence of various compounds.
Electromagnetic spectrum: The electromagnetic spectrum encompasses all types of electromagnetic radiation, ranging from gamma rays with the shortest wavelengths to radio waves with the longest wavelengths. In organic chemistry, it plays a crucial role in structure determination by providing information about molecular vibrations and ion fragmentation patterns.
Electromagnetic Spectrum: The electromagnetic spectrum is the entire range of electromagnetic radiation, which includes various types of energy waves such as radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. This spectrum is organized based on the wavelength and frequency of the different forms of radiation, and it plays a crucial role in various areas of science, including organic chemistry.
Ester: An ester is a chemical compound formed by the reaction between an organic acid and an alcohol, resulting in the replacement of the hydrogen atom of the acid by an alkyl or aryl group. Esters are widely encountered in various topics in organic chemistry, including functional groups, oxidation-reduction reactions, alcohol formation, and spectroscopy.
Functional Group Analysis: Functional group analysis is the process of identifying and characterizing the specific functional groups present in a chemical compound. This analytical technique is crucial in organic chemistry for understanding the reactivity, properties, and potential transformations of molecules.
Infrared Spectroscopy: Infrared spectroscopy is an analytical technique that uses the infrared region of the electromagnetic spectrum to identify and characterize the chemical composition of a sample. It provides information about the molecular structure and functional groups present in a compound by analyzing the absorption or emission of infrared radiation.
IR Spectroscopy: IR spectroscopy is a technique that uses infrared radiation to identify and analyze the molecular structure of organic compounds. It provides information about the vibrational modes of chemical bonds, allowing for the identification of functional groups and the determination of the overall structure of a molecule.
Jones Oxidation: The Jones oxidation is a chemical reaction used to selectively oxidize primary and secondary alcohols to their corresponding aldehydes and ketones, respectively. It is a powerful tool in organic chemistry for the controlled conversion of alcohols to carbonyl compounds.
Mass Spectrometry: Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of ions to identify and quantify the chemical composition of a sample. It provides detailed information about the molecular structure and fragmentation patterns of compounds, making it a powerful tool in organic chemistry and various other fields.
Mass spectrometry (MS): Mass spectrometry is an analytical technique used in organic chemistry to determine the mass-to-charge ratio of ions. It helps identify the composition of a sample by generating ions and measuring their mass and charge.
Molecular Fragmentation: Molecular fragmentation refers to the process by which larger molecules are broken down into smaller fragments or ions during various analytical techniques, such as mass spectrometry. This process provides valuable information about the structure and composition of the original molecule.
Molecular Vibrations: Molecular vibrations refer to the oscillatory motion of atoms within a molecule around their equilibrium positions. This dynamic behavior of molecules is a fundamental aspect of spectroscopy and is crucial for understanding infrared and other types of molecular spectra.
NMR Spectroscopy: NMR (Nuclear Magnetic Resonance) spectroscopy is an analytical technique that uses the magnetic properties of atomic nuclei to provide detailed information about the structure and composition of organic compounds. It is a powerful tool for identifying and characterizing chemical compounds, particularly in the context of organic chemistry.
Nuclear Spin: Nuclear spin is a fundamental property of atomic nuclei that arises from the angular momentum of protons and neutrons within the nucleus. This intrinsic spin of the nucleus is a critical concept in understanding various spectroscopic techniques, including NMR spectroscopy.
O-H Stretch: The O-H stretch refers to the vibrational mode of the hydroxyl (O-H) group, which is a common functional group in organic compounds. This stretch involves the periodic lengthening and shortening of the O-H bond, and it is a key feature in the spectroscopic analysis of carboxylic acid derivatives.
Tetramethylsilane: Tetramethylsilane (TMS) is a colorless, volatile liquid compound with the chemical formula Si(CH3)4. It is widely used as a standard reference compound in nuclear magnetic resonance (NMR) spectroscopy due to its unique properties that make it an ideal internal standard for 1H and 13C NMR experiments.