Name: ir and nmr signatures of acid derivatives
Uploaded: 2023-04-30T10:21:11.000Z
Duration: 1 min 26 s
Channel: JoVE

The IR spectra of all carboxylic acid derivatives exhibit a typical carbonyl stretching absorption between 1650 and 1850 cm&#8722;1.
For instance, esters show an absorption around 1740 cm&#8722;1, and acid halides exhibit absorption around 1800 cm&#8722;1.
In contrast,&#160; acid anhydrides exhibit two carbonyl absorptions due to the symmetrical and unsymmetrical vibrations from carbonyl stretching.
Interestingly, nitriles produce a strong characteristic absorption at a higher frequency due to the stretching of the polar carbon&#8211;nitrogen triple bond.
Conversely, amides exhibit a lower carbonyl absorption frequency due to the conjugation effect.
In 1H NMR, the highly deshielded acidic protons absorb far downfield around 10&#8211;12 ppm, whereas the protons of the &#945;-carbon absorb around 2&#8211;2.5 ppm.
&#160;In 13C NMR, the carbonyl carbon of derivatives shows absorption around 160&#8211;185 ppm.
However, the nitrile carbon absorbs around 115&#8211;130 ppm due to sp hybridized carbon.

spectroscopy of carboxylic acid derivatives

Spectroscopy of Carboxylic Acid Derivatives

Infrared spectroscopy is primarily used to determine the types of bonds and functional groups. In carboxylic acid derivatives, a typical carbonyl bond absorption is observed around 1650&#8211;1850 cm&#8722;1. For esters, the absorption is recorded at around 1740 cm&#8722;1, while acid halides show the absorption at about 1800 cm&#8722;1. Another acid derivative, the acid anhydrides, exhibit two carbonyl absorption around 1760 cm&#8722;1 and 1820 cm&#8722;1, arising from the symmetrical and unsymmetrical carbonyl vibration.
In the case of nitriles, the polar carbon&#8211;nitrogen triple bond stretching produces a strong absorption at a higher frequency, around 2200 cm&#8722;1. In comparison, the carbonyl stretching of an amide occurs at a lower frequency, around 1660 cm&#8722;1, which can be attributed to the conjugation effect. Conjugation in the carbonyl compounds delocalizes the &pi; electrons, inducing a partial single bond character. Consequently, the bond requires less energy to stretch and absorbs at lower frequencies.
Interestingly, decreasing ring size in cyclic derivatives increases the ring strain, thereby increasing carbonyl absorption frequency.
The 1H NMR spectra of carboxylic acid derivatives show a peak around 10&#8211;12 ppm for highly shielded acidic protons, and the peak for the protons of the &alpha; carbon is observed around 2&#8211;2.5 ppm. In the 13C NMR spectra, the carbonyl carbon shows a distinct peak around 160&#8211;185 ppm. The absorption of the nitrile carbon is observed at a lower frequency.

Infrared spectroscopy is primarily used to determine the types of bonds and functional groups. In carboxylic acid derivatives, a typical carbonyl bond ...

spectroscopy-of-carboxylic-acid-derivatives

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Organic Chemistry

Unit 1

Carboxylic Acid Derivatives

KEY TERMS AND CONCEPTS

ir and nmr signatures of acid derivatives

Infrared spectroscopy helps identify bonds and functional groups in carboxylic acid derivatives. Their carbonyl group usually absorbs in the 1650 to 1850 cm −1 range. These peaks shift depending on the type of derivative, so the spectrum can help tell related compounds apart.

Esters usually show a carbonyl absorption around 1740 cm −1. Acid halides absorb near 1800 cm −1. Acid anhydrides give two carbonyl peaks, one around 1760 cm −1 and another around 1820 cm −1. These two bands come from symmetrical and unsymmetrical carbonyl vibrations.

Nitriles are different because they contain a carbon-nitrogen triple bond. That bond gives a strong absorption around 2200 cm −1, which appears at a higher frequency than a carbonyl stretch. Amides absorb at a lower frequency, around 1660 cm −1. This lower value is linked to conjugation, which spreads out the pi electrons and gives the carbonyl more partial single-bond character.

Ring size also affects the carbonyl signal in cyclic derivatives. As the ring gets smaller, ring strain increases. That extra strain raises the carbonyl absorption frequency.

Carboxylic acid derivatives also show useful NMR signals. In 1H NMR, highly shielded acidic protons appear around 10 to 12 ppm, and alpha carbon protons appear around 2 to 2.5 ppm. In 13C NMR, the carbonyl carbon gives a distinct peak around 160 to 185 ppm. The nitrile carbon appears at a lower frequency.

IR and NMR Signatures of Acid Derivatives

ir-and-nmr-signatures-of-acid-derivatives

carboxylic acid derivatives: overview

Common Carboxylic Acid Derivative Types

Carboxylic acid derivatives are organic compounds made when the hydroxyl group of a carboxylic acid is replaced by another functional group. These compounds still contain a carbonyl group, which is a carbon atom double-bonded to oxygen. A related group, nitriles, has a cyano group with a carbon triple-bonded to nitrogen. The main carboxylic acid derivatives are acid halides, acid anhydrides, esters, and amides. Cyclic esters are called lactones, and cyclic amides are called lactams. Acid...

nomenclature of carboxylic acid derivatives: acid halides, esters, and acid anhydrides

nomenclature-carboxylic-acid-derivatives-acid-halides-esters-acid

Naming Acid Halides, Esters, and Anhydrides

Acid halides, esters, and acid anhydrides are named from their parent carboxylic acids using a few clear IUPAC and common-name rules. These naming patterns help identify the compound type and the group attached to the acid structure. For acid halides, the name comes from the matching carboxylic acid. The ending "ic acid" is changed to "yl halide," so ethanoic acid gives ethanoyl chloride, while the common name acetic acid gives acetyl chloride. Cyclic acid halides use a different pattern. The...

nomenclature of carboxylic acid derivatives: amides and nitriles

nomenclature-of-carboxylic-acid-derivatives-amides-and-nitriles

Amides and Nitriles: IUPAC Naming Rules

Amides and nitriles are named with a few clear IUPAC rules and common-name patterns. For amides, the parent carboxylic acid name changes by replacing the ending "oic acid" or "ic acid" with "amide." For example, ethanamide comes from ethanoic acid, and the common name acetamide comes from acetic acid. Substituents on the nitrogen atom of an amide are written with N- labels. A methyl group gives N-methylethanamide, and two methyl groups give N,N-dimethylethanamide. If the groups are different,...

structures of carboxylic acid derivatives

structures-of-carboxylic-acid-derivatives

Carboxylic Acid Derivatives: Bonding and Shape

Carboxylic acid derivatives have an acyl group attached to a heteroatom such as chlorine, oxygen, or nitrogen. Their bonding pattern helps explain both their shape and their stability. In these compounds, the carbonyl carbon and oxygen are both sp2-hybridized and each has an unhybridized p orbital. The three sp2 orbitals on the carbonyl carbon form three sigma bonds. One bond is to the carbonyl oxygen, one is to the alpha carbon, and one is to the heteroatom. The other two sp2 orbitals on the...

physical properties of carboxylic acid derivatives

physical-properties-of-carboxylic-acid-derivatives

Boiling Points and Solubility of Derivatives

Carboxylic acid derivatives show different boiling points, melting points, and solubilities because of intermolecular forces. Intermolecular forces are attractions between molecules. They include ionic forces, hydrogen bonds, dipole-dipole forces, and dispersion forces. Ionic forces are the strongest, and dispersion forces are the weakest. Among carboxylic acid derivatives, acid chlorides and esters have very similar boiling points. They are also the lowest in the group. Acid anhydrides have...

acidity and basicity of carboxylic acid derivatives

acidity-and-basicity-of-carboxylic-acid-derivatives

Relative Acid Strength in Carboxylic Derivatives

Carboxylic acids are the strongest organic acids. They lose the hydroxyl proton easily and form a resonance-stabilized carboxylate ion. That stable conjugate base helps explain their acidity. Carboxylic acid derivatives behave differently because they do not have acidic hydrogens directly attached to the main functional group. Their weak acidity comes from losing alpha hydrogens, which are hydrogens on the carbon next to the functional group. The acid strength of these derivatives depends on...

Infrared spectroscopy helps identify bonds and functional groups in carboxylic acid derivatives. Their carbonyl group usually absorbs in the 1650 to 1850 cm −1 range. These peaks shift depending on the type of derivative, so the spectrum can help tell related compounds apart. Esters usually show a carbonyl absorption around 1740 cm −1. Acid halides absorb near 1800 cm −1. Acid anhydrides give two carbonyl peaks, one around 1760 cm −1 and another around 1820 cm −1. These two bands come from...

relative reactivity of carboxylic acid derivatives

relative-reactivity-of-carboxylic-acid-derivatives

Reactivity Order of Carboxylic Acid Derivatives

Carboxylic acid derivatives react with nucleophiles in different ways. Acid halides, anhydrides, esters, and amides can all undergo nucleophilic acyl substitution. Their reactivity depends on the group attached to the carbonyl carbon. A major factor is the basicity of the leaving group. A weaker base leaves more easily, so the derivative is more reactive. The leaving-group basicity order is halide ions, acyloxy ions, alkoxy ions, then amine ions. That is why acid halides are the most reactive...

nucleophilic acyl substitution of carboxylic acid derivatives

nucleophilic-acyl-substitution-of-carboxylic-acid-derivatives

How Acyl Groups Change in Substitution

Nucleophilic acyl substitution changes one carboxylic acid derivative into another. It is a key substitution reaction in organic chemistry. The reaction involves a nucleophile and an acyl compound, such as carboxylic acids and their derivatives. The reaction begins when the nucleophile attacks the carbonyl carbon. This step is called addition. It forms a tetrahedral intermediate, which is a temporary four-sided structure around the carbonyl carbon. Next, the leaving group attached to the acyl...

acid halides to carboxylic acids: hydrolysis

acid-halides-to-carboxylic-acids-hydrolysis

Water Attack on Acid Halides

Acid halides react with water in a nucleophilic acyl substitution reaction to form carboxylic acids. This reaction happens readily and does not need an acid catalyst or a base catalyst. The mechanism begins when water acts as a nucleophile and attacks the carbonyl carbon. This forms a tetrahedral intermediate. The carbon-oxygen pi bond then reforms, and a halide ion leaves. A final proton transfer gives the carboxylic acid product. The reaction also produces hydrochloric acid, HCl, which is...

acid halides to esters: alcoholysis

Alcohol Reactions with Acid Halides

Alcohol reacts with acid halides in a nucleophilic acyl substitution reaction to form esters. In this reaction, the alcohol serves as the nucleophile and attacks the acyl carbon. This step starts the conversion from an acid halide to an ester. The mechanism moves in three steps. First, the alcohol attack forms a tetrahedral intermediate. Next, the carbonyl group reforms and chloride leaves. Then the positively charged intermediate loses a proton, giving the ester product. H3O+ is also formed,...

acid halides to amides: aminolysis

Amines in Acyl Chloride Substitution

Amines in acyl chloride substitution show how acid halides react with ammonia or amines to form amides. This nucleophilic acyl substitution uses the amine as the nucleophile, and the product depends on the amine type. Acid halides can react with ammonia, primary amines, and secondary amines. These reactions produce primary, secondary, and tertiary amides, respectively. The aminolysis pathway is the same type of substitution in each case. The mechanism begins when the amine attacks the...

acid halides to alcohols: lialh4 reduction

acid-halides-to-alcohols-lialh4-reduction

Reducing Acid Halides with LiAlH4

Acid halides can be reduced to primary alcohols with lithium aluminum hydride, or LiAlH4, a strong reducing agent. The reaction starts when a hydride ion, which acts as a nucleophile, attacks the carbonyl carbon of the acid halide. This forms a tetrahedral intermediate. The carbonyl group then forms again, and the halide ion leaves as a leaving group. That step creates an aldehyde. A second hydride attack gives an alkoxide ion, and protonation of the alkoxide produces the final primary alcohol.

acid halides to alcohols: grignard reaction

acid-halides-to-alcohols-grignard-reaction

Grignard Reagents Make Tertiary Alcohols

Grignard reagents, also called organomagnesium halides, can turn acid halides into tertiary alcohols. This reaction uses two equivalents of the Grignard reagent and goes through a ketone intermediate. A Grignard reagent acts as a nucleophile, which means it donates electron-rich carbon in the form of a carbanion. The carbanion attacks the carbonyl carbon of the acid halide and forms a tetrahedral intermediate. The carbonyl group then forms again, the halide ion leaves, and a ketone is produced.

acid halides to ketones: gilman reagent

Gilman Reagent: Stop at the Ketone

Gilman reagent lets an acid chloride stop at the ketone stage. Lithium dialkyl cuprate reacts with acid halides and gives ketones in good yield. For this reaction, the acid chloride is treated with the reagent at −78 °C in ether solution. The reaction happens in two steps. First, one alkyl group on the Gilman reagent acts as a nucleophile, meaning it donates a pair of electrons. It attacks the acyl carbon of the acid chloride and forms a tetrahedral intermediate. Next, the carbon–oxygen...

preparation of acid anhydrides

Methods for Making Acid Anhydrides

Acid anhydrides can be made by reacting acid chlorides with carboxylic acid salts. In this nucleophilic acyl substitution, the carboxylate ion acts as the nucleophile. It attacks the carbonyl carbon of the acid chloride and forms a tetrahedral intermediate. The intermediate then breaks down as the carbonyl group reforms. Chloride leaves as the leaving group, and the acid anhydride is formed. A similar route uses an acid chloride and a carboxylic acid in the presence of pyridine. Pyridine...

reactions of acid anhydrides

Acid Anhydride Reactions and Products

Acid anhydrides react by nucleophilic acyl substitution. In this process, a nucleophile attacks one carbonyl group, and the second carbonyl group becomes part of the leaving group. The reaction is similar to acid chloride reactions, but the leaving group is a carboxylate ion instead of a chloride ion. When acid anhydrides react with water, they hydrolyze to give two equivalents of carboxylic acid. In alcoholysis, an alcohol acts as the nucleophile and forms an ester plus a carboxylic acid.

esters to carboxylic acids: saponification

esters-to-carboxylic-acids-saponification

Saponification and Soap-Making from Esters

Saponification is the base-promoted hydrolysis of esters. In this reaction, an ester reacts with an aqueous base and then an acid to form a carboxylic acid. It is closely linked to soap-making from fats.

esters to carboxylic acids: acid-catalyzed hydrolysis

esters-to-carboxylic-acids-acid-catalyzed-hydrolysis

How Acid Speeds Ester Hydrolysis

Acid-catalyzed ester hydrolysis breaks an ester into a carboxylic acid and an alcohol. In excess water, the reaction is reversible and follows a nucleophilic acyl substitution pathway. It is also the exact reverse of a Fischer esterification reaction. The acid catalyst starts the reaction by protonating the ester carbonyl oxygen. This protonation makes the carbonyl carbon more electrophilic, which means it is more likely to be attacked by a nucleophile. Water then adds to the carbonyl carbon...

esters to alcohols: hydride reductions

Reducing Esters to Primary Alcohols

Esters can be reduced to primary alcohols with a strong reducing agent such as lithium aluminum hydride. This reaction uses two equivalents of the reducing agent and goes through an aldehyde intermediate before the final alcohol forms. Lithium aluminum hydride is a source of hydride ions. A hydride ion is a nucleophile, which means it donates an electron pair. In the first step, the hydride attacks the carbonyl carbon of the ester and forms a tetrahedral intermediate. Next, the carbonyl group...

esters to alcohols: grignard reaction

Grignard Reagents in Ester Alcohol Synthesis

Esters can react with Grignard reagents to form alcohols after hydrolysis. This reaction uses two equivalents of the Grignard reagent and adds two identical alkyl groups to the carbon that will hold the hydroxyl group. For most esters, the final product is a tertiary alcohol. For formate esters, the product is a secondary alcohol. The reaction follows a nucleophilic acyl substitution mechanism. A Grignard reagent is a carbanion source, so it acts as a nucleophile and attacks the carbonyl...

preparation of amides

Amide Formation from Carboxylic Acids

Amide formation from carboxylic acids uses amines and a dehydrating agent to build the amide bond. A common reagent is dicyclohexylcarbodiimide, or DCC. It helps drive the reaction toward the product by activating the acid first. In the DCC-promoted route, the carboxylic acid protonates DCC. This makes DCC a better acceptor. Then the carboxylate adds to the protonated carbodiimide and forms a reactive acylating agent. Next, the amine acts as a nucleophile and attacks that intermediate to make...

amides to carboxylic acids: hydrolysis

Amide Hydrolysis Under Acid and Base

Amide hydrolysis breaks an amide into a carboxylic acid using either acidic or basic conditions. The reaction is a nucleophilic acyl substitution, which means a nucleophile attacks the carbonyl carbon and the acyl group is changed. Both pathways need strong conditions and heat because amides are slow to react. In acid-catalyzed hydrolysis, the acid first protonates the carbonyl oxygen. This makes the amide carbonyl carbon more electrophilic, or more likely to be attacked by a nucleophile.

amides to amines: lialh4 reduction

How LiAlH4 Turns Amides into Amines

Lithium aluminum hydride, or LiAlH4, reduces amides to amines through nucleophilic acyl substitution. In this reaction, a strong reducing agent supplies hydride ions, which can add to the carbonyl group. Primary, secondary, and tertiary amides give primary, secondary, and tertiary amines, respectively. The reduction starts when a hydride ion attacks the carbonyl carbon. This forms a tetrahedral intermediate. Next, the carbonyl oxygen bonds to aluminum hydride, creating an oxygen-aluminum bond.<br...

preparation of nitriles

Making Nitriles from Amides and Halides

Nitriles can be made by turning amides into nitriles through dehydration. This reaction uses strong dehydrating agents such as phosphorous pentoxide or boiling acetic anhydride. Thionyl chloride can also drive the same change, and in that reaction the amide acts as a nucleophile, a molecule that donates an electron pair. The mechanism with thionyl chloride begins when the amide attacks the reagent to form an intermediate. Next, electron pairs shift and a chloride ion leaves. A deprotonation...

nitriles to carboxylic acids: hydrolysis

Turning Nitriles into Carboxylic Acids

Nitriles can be converted into carboxylic acids by hydrolysis. This reaction can happen under acidic conditions or basic conditions. In both cases, the change goes through an amide intermediate before the final carboxylic acid forms. In acid-catalyzed hydrolysis, the nitrogen atom is protonated first. This makes the nitrile carbon more open to attack. Water then attacks the nitrile carbon. After deprotonation, the product becomes a tautomeric form of an amide. Protonation of nitrogen then...

nitriles to ketones: grignard reaction

Grignard Reagent Forms Ketones from Nitriles

Grignard reagents can turn nitriles into ketones by forming a new carbon-carbon bond. This reaction follows a nucleophilic acyl substitution pathway, which means a nucleophile attacks a carbonyl-related carbon and then the product changes in later steps. Organomagnesium halides are commonly called Grignard reagents. Their alkyl-magnesium bond is highly polar, so the alkyl carbon has carbanionic character and acts as the nucleophile. First, it attacks the nitrile carbon and forms an anion, also...

nitriles to amines: lialh4 reduction

Reducing Nitriles with LiAlH4

The mechanism occurs in three steps. First, a hydride ion acts as a nucleophile and attacks the nitrile carbon to form an anion. Then a second hydride ion attacks that anion to give a dianion. Water then protonates the dianion and produces a primary amine as the final product.

key terms and concepts

Learn how IR and NMR reveal carboxylic acid derivatives, from ester, amide, and anhydride carbonyl peaks to nitrile and alpha-carbon signals.

IR and NMR Signatures of Acid Derivatives | JoVE K12

organic chemistry

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IR and NMR Signatures of Acid Derivatives

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