Organic Chemistry -Infrared Spectroscopy
-Ultraviolet Spectroscopy
Test Study Guide: -Nuclear Magnetic
Resonance Spectroscopy
Ch.11 Spectroscopy -And More
CONCEPT SUMMARY
Infrared Spectroscopy
Measurement Principle
Infrared (IR) spectroscopy measures the absorption of infrared light, which induces molecular vibrations such
as stretching, bending, twisting, and folding.
Spectral Representation
IR spectra are typically plotted as percent transmittance versus wavenumber (cm^-1).
Wavenumber Range
The normal range for an IR spectrum spans from 4000 to 400 cm^-1.
Fingerprint Region
The fingerprint region is located between 1500 and 400 cm^-1. This area contains numerous peaks that
experts can utilize to identify specific compounds.
Bond Vibration and Dipole Moment
For a bond’s vibration to be detected in an IR spectrum, it must result in a change in the bond dipole moment.
Certain bonds exhibit characteristic absorption frequencies, enabling the inference of particular functional
groups’ presence or absence.
Characteristic Absorption Peaks
The O-H peak appears as a broad peak around 3300 cm^-1. Molecules containing O-H groups include
alcohols, water, and carboxylic acids. Notably, the O-H peak for carboxylic acids is shifted to around 3000
cm^-1.
N-H and C=O Peaks in Infrared Spectroscopy
N-H Peak: Sharp peak observed around 3300 cm⁻¹, indicative of molecules containing N-H groups such as
amines, imines, and amides.
C=O Peak: Sharp peak found around 1750 cm⁻¹, associated with various functional groups including
aldehydes, ketones, carboxylic acids, amides, esters, and anhydrides.
Ultraviolet Spectroscopy
Measurement Principle: Ultraviolet (UV) spectroscopy involves the absorption of UV light which facilitates
electron transitions between molecular orbitals.
-Ultraviolet Spectroscopy
Test Study Guide: -Nuclear Magnetic
Resonance Spectroscopy
Ch.11 Spectroscopy -And More
CONCEPT SUMMARY
Infrared Spectroscopy
Measurement Principle
Infrared (IR) spectroscopy measures the absorption of infrared light, which induces molecular vibrations such
as stretching, bending, twisting, and folding.
Spectral Representation
IR spectra are typically plotted as percent transmittance versus wavenumber (cm^-1).
Wavenumber Range
The normal range for an IR spectrum spans from 4000 to 400 cm^-1.
Fingerprint Region
The fingerprint region is located between 1500 and 400 cm^-1. This area contains numerous peaks that
experts can utilize to identify specific compounds.
Bond Vibration and Dipole Moment
For a bond’s vibration to be detected in an IR spectrum, it must result in a change in the bond dipole moment.
Certain bonds exhibit characteristic absorption frequencies, enabling the inference of particular functional
groups’ presence or absence.
Characteristic Absorption Peaks
The O-H peak appears as a broad peak around 3300 cm^-1. Molecules containing O-H groups include
alcohols, water, and carboxylic acids. Notably, the O-H peak for carboxylic acids is shifted to around 3000
cm^-1.
N-H and C=O Peaks in Infrared Spectroscopy
N-H Peak: Sharp peak observed around 3300 cm⁻¹, indicative of molecules containing N-H groups such as
amines, imines, and amides.
C=O Peak: Sharp peak found around 1750 cm⁻¹, associated with various functional groups including
aldehydes, ketones, carboxylic acids, amides, esters, and anhydrides.
Ultraviolet Spectroscopy
Measurement Principle: Ultraviolet (UV) spectroscopy involves the absorption of UV light which facilitates
electron transitions between molecular orbitals.
