Inorgnic and Analytical Chemistry

Dr. Muhammad Afzal SubhaniSchool of Chemical & Materials EngineeringNUST H-12 Islamabad

Course CHEM-101

Mass, NMR and IR Spectroscopy

IR Spectroscopy

Principles

• Absorption of electromagnetic radiation in the infrared region of the spectrum resulting in changes in the vibrational energy of molecules.

Instrumentation

• IR spectrometer or double-beam spectrophotometer

• incorporating prism or grating monochromator,

• thermal or photon detector,

• alkali halide cells.

Applications

• largely for the identification and structural analysis of organic materials

• Near infrared region used increasingly for industrial quality control.

Disadvantages

• Difficult to analyse mixtures. Special cells required for aqueous samples.

IR Spectroscopy

IR Spectrophotometer

IR Spectroscopy

The first question that which bond will vibrate?

• much stronger or weaker than others nearby

or• between atoms that are much heavier

or lighter than their neighbours• The relationship between frequency of

the bond vibration, the mass of the atoms, and thestrength of the bond is described by equation 1

• Where;

– f is force constant more or less bond strength

– μ is Reduced mass which is given by equation 2

equation 1 equation 2

IR Spectroscopy

What Kind of IR spectra is?

IR Spectroscopy

Kind of Vibrations

X—H Vibrations

Saturated and unsaturated groups

IR Spectroscopy

IR Spectroscopy

IR Spectroscopy

The X–H IR stretches are very different in these four compounds.

Mass spectrometry

Mass spectrometry

Introduction

• It gives information about molecular weight and composition of a compound

Instrumentation

• A source to volatilize and ionize the molecule into a beam of charged particles

• something to focus the beam so that particles of the same mass:charge ratio are separated from all others

• A detector to detect the particles

• All spectrometers in common use operate in a high vacuum

Mass spectrometry

Mass spectrometry

Mass spectrometry by electron impact

Mass spectrometry