JoVE Logo

登录

In ¹H NMR spectroscopy, acidic protons (–COOH) of carboxylic acids are highly deshielded and absorb far downfield, at around 9–12 ppm. The chemical shift value depends on the concentration and solvent used.

While α protons of carboxylic acids absorb at 2–2.5 ppm, β protons absorb further upfield.

Carboxylic acids are easily identified by dissolving them in deuterium oxide, which results in a rapid exchange of the acidic protons with deuterium. This leads to the disappearance of the acidic proton signal in the spectrum.

In 13C NMR spectroscopy of carboxylic acids, carbonyl carbons absorb around 160–180 ppm. However, they absorb at a lower chemical shift (or at a higher field) than the aldehydes and ketones’ carbonyl carbons. It is due to the high shielding effect of the carboxylate oxygen’s unshared pair of electrons. α carbons of carboxylic acids absorb at 20–40 ppm.

In mass spectroscopy, carboxylic acids show a small molecular ion peak. McLafferty fragmentation of carboxylic acids yields even-numbered mass fragment ions (base peak) with the loss of an alkene. Another prominent fragmentation happens with the loss of an alkyl radical, yielding a resonance-stabilized cation (has odd mass). Aromatic carboxylic acids give prominent fragment ion peaks with the loss of –OH and –C=O, apart from the molecular ion peaks.

Tags

NMR SpectroscopyMass SpectroscopyCarboxylic AcidsAcidic ProtonsChemical ShiftDeuterium OxideCarbonyl CarbonsMcLafferty FragmentationMass Fragment IonsResonance stabilized Cation

来自章节 13:

article

Now Playing

13.6 : NMR and Mass Spectroscopy of Carboxylic Acids

Carboxylic Acids

3.6K Views

article

13.1 : IUPAC 羧酸命名法

Carboxylic Acids

8.7K Views

article

13.2 : 羧酸的物理性质

Carboxylic Acids

4.4K Views

article

13.3 : 羧酸的酸度

Carboxylic Acids

6.5K Views

article

13.4 : 取代基对羧酸酸度的影响

Carboxylic Acids

6.4K Views

article

13.5 : 羧酸的红外和紫外-可见光谱

Carboxylic Acids

3.6K Views

article

13.7 : 羧酸的制备:概述

Carboxylic Acids

2.4K Views

article

13.8 : 羧酸的制备:腈的水解

Carboxylic Acids

3.8K Views

article

13.9 : 羧酸的制备:格氏试剂的羧化

Carboxylic Acids

4.2K Views

article

13.10 : 羧酸的反应:简介

Carboxylic Acids

2.9K Views

article

13.11 : 羧酸制酯:酸催化 (Fischer) 酯化概述

Carboxylic Acids

17.7K Views

article

13.12 : 羧酸制酯:酸催化 (Fischer) 酯化机制

Carboxylic Acids

7.6K Views

article

13.13 : 羧酸制甲酯:使用重氮甲烷进行烷基化

Carboxylic Acids

2.0K Views

article

13.14 : 羧酸制酰氯

Carboxylic Acids

6.6K Views

article

13.15 : 羧酸制伯醇:氢化物还原

Carboxylic Acids

2.6K Views

See More

JoVE Logo

政策

使用条款

隐私

科研

教育

关于 JoVE

版权所属 © 2025 MyJoVE 公司版权所有,本公司不涉及任何医疗业务和医疗服务。