4.7 - analttical techniques

Question 1

How do covalent bonds act

Answer 1

like springs

Question 2

How can covalent bonds vibrate

Answer 2

they can stretch or bend
symmetrically or asymmetrically

Question 3

What part of the EM spectrum does vibration occur

Answer 3

The IR region

Question 4

What is resonance

Answer 4

If an organic molecule is irradiated with infra-red energy that matches the natural vibration
frequency of its bonds, it absorbs some of that energy and the amplitude of vibration
increases

Question 5

How does Ir spectroscopy work

Answer 5

Infrared (IR) spectroscopy is a technique used to identify compounds based on changes in
vibrations of atoms when they absorb IR of certain frequencies

A spectrophotometer irradiates the sample with IR radiation and then detects the intensity
of IR radiation absorbed by the molecule

IR energy is absorbed only if a molecule has a permanent dipole that changes as it vibrates

Symmetrical molecules such as O2 or H2, are therefore IR inactive

The resonance frequency is the specific frequency at which the bonds will vibrate

Rather than displaying frequency, an IR spectrum shows a unit called wavenumber

Wavenumber is the reciprocal of the wavelength and has units of cm

Characteristic absorptions can be matched to specific bonds in molecules

This enables chemists to determine the functional groups present

Question 6

What are 2 other uses of infrared spectroscopy

Answer 6

to identify pollutants in vehicle emissions in the air

to measure alcohol levels using roadside breathalysers

Question 7

what is the fingerprint region

Answer 7

1500cm

unique for all molecules