Chapter 17 Analytical Techniques And Spectroscopy

Question 1

What does Infrared Radiation cause?

Answer 1

Causes covalent bonds to vibrate more and absorb energy.

The amount a nod stretches depends on:
The mass of the atoms in the bond - heavier atoms vibrate more slowly
The strength fo the bond - stronger bonds vibrate faster

Question 2

How does infrared radiation influence atmospheric gases like carbon dioxide, water vapour and methane?

Answer 2

These gases absorbed the longer-wavelength IR radiation that have been remitted from the earths surface, this is because it has the same frequency as the natural frequency of their bonds.
Eventually the vibrating bonds in these molecules re-emit this energy as radiation that increases the temperature of the atmosphere close to the earths surface, leading to global warming.

Question 3

What does infrared spectroscopy help you do?

Answer 3

Identify the functional groups present in organic molecules

Question 4

How has infrared spectroscopy be applied to other situations (other than organic compound identification)?

Answer 4

• can be used to analyse vehicle emissions to detect and measure carbon monoxide, carbon dioxide and hydrocarbons in busy town centres or by motorways to monitor localised pollution
• IR-based breathalysers pass a beam of IR radiation through the captured breath in the sample chamber and detects the IR absorbance of the compounds in the breath. The more IR absorbed, the higher the reading, and the more ethanol in the breath

Question 5

How can the molecular ion leak be detected in a mass spectrum?

Answer 5

When an organic product is put into a mas spectrometer it loses an electron and forms a positive ion, the molecular mass spectrometer detects the mass-to-chigre ratio (m/z) of the molecular ion which gives the molecular mass of the compound.

The M+ peak (molecular ion peak) is the clear peak at the highest m/z value on the right hand side of the spectrum.

Question 6

What is the M+1 peak?

Answer 6

Due to isotopic variations, you may also see a very small peak one unit after the M+ peak. This is because 1.1% of carbon is the carbon-13 isotope

Question 7

How can fragmentation give more information as to the structure of the compound?

Answer 7

In the mass spectrometer doe, molecular ions break down into smaller pieces known as fragments in a process called fragmentation.

The mass spectrum of each compound is unique as they form their own distinctive fragments which means that fragment ions can be used to differentiate between structural isomers