FTIR INSTRUMENTATION AND FUNCTIONAL GROUP DETERMINATION 01.09.2025

Описание: Educational video
FTIR INSTRUMENTATION AND FUNCTIONAL GROUP 01.09.2025
FTIR Instrumentation and Functional Group Determination
1. Instrumentation (FTIR Setup)
Fourier Transform Infrared (FTIR) spectrometer is used to record infrared spectra of a sample. The basic components are:

Infrared Source

A broadband IR source (commonly a heated Globar (silicon carbide rod)) emits IR radiation covering ~4000–400 cm⁻¹.

Interferometer

Heart of FTIR.

Most commonly a Michelson interferometer splits the IR beam into two paths using a beam splitter (usually KBr).

One beam reflects off a stationary mirror, the other off a moving mirror.

The beams recombine to produce an interference pattern (interferogram) containing all IR frequencies simultaneously.

Sample Compartment

The IR beam passes through the sample (solid, liquid, or gas).

Some frequencies are absorbed depending on the molecular vibrations of bonds present.

Transmission or reflectance modes can be used.

Detector

Measures the intensity of transmitted IR light.

Common detectors: DTGS (deuterated triglycine sulfate), MCT (mercury cadmium telluride, more sensitive).

Computer (Fourier Transform)

The interferogram is mathematically converted into a spectrum (Intensity vs Wavenumber) using Fourier Transform.

Final output = FTIR spectrum.

2. Principle of Functional Group Determination
Molecules absorb IR radiation at frequencies corresponding to their bond vibrations (stretching, bending, twisting).

Each functional group has a characteristic absorption range, which acts as a “fingerprint”.

3. Major Functional Groups and their FTIR Peaks
Here are the common diagnostic regions (in cm⁻¹):

(A) Functional Group Region (4000–1500 cm⁻¹)
O–H stretch (alcohols, phenols): 3200–3600 (broad, strong)

N–H stretch (amines, amides): 3300–3500 (sharper than O–H)

C–H stretch (alkanes): 2850–2960

C=H stretch (alkenes): 3010–3100

≡C–H stretch (alkynes): ~3300 (sharp)

C≡C stretch: 2100–2260 (weak)

C≡N stretch (nitriles): 2210–2260 (sharp)

C=O stretch (carbonyls): 1650–1750 (very strong, sharp)

Aldehydes: 1720–1740

Ketones: 1705–1725

Carboxylic acids: 1700–1725 (plus broad O–H at 2500–3300)

Esters: 1735–1750

Amides: 1640–1690

C=C stretch (alkenes, aromatics): 1600–1680

(B) Fingerprint Region (1500–400 cm⁻¹)
Contains complex vibrations unique to each molecule.

Used for compound identification by comparison to reference spectra.

✅ Summary:
FTIR works by passing infrared light through a sample and analyzing absorption due to bond vibrations. Each functional group has a unique absorption range, allowing us to identify them and confirm molecular structure.