3.3.6 Organic analysis

Question 1

What is mass spectrometry used for?

Answer 1

To determine the molecular formula of a compound.

Question 2

What is high resolution mass spectrometry?

Answer 2

It can determine the mass of a peak to several decimal places so that we can distinguish between compounds that have a similar Mr but different empirical formulae.

Question 3

What happens in IR spectroscopy?

Answer 3

Shine different frequencies of IR through a sample of organic compound.
Bonds in a molecule absorb IR at characteristic wavelengths and frequencies.
Detector finds the frequencies that passed through with no loss.

Question 4

What happens when the bonds in a molecule absorb IR?

Answer 4

Molecules go from a vibrational state to an excited vibrational state.
This causes a change in dipole moment.
Which can cause several movements like: wagging, scissors, rocking, asymmetric stretching, symmetric stretching

Question 5

Which molecules strongly absorb IR?

Answer 5

Greenhouse gases:
Methane
Water vapour
Carbon dioxide

Question 6

Which molecules aren’t so good at absorbing IR?

Answer 6

Nitrogen and oxygen. They make up the majority of the atmosphere and can’t absorb IR as the vibrations don’t change their dipole moments.

Question 7

What is shown on an IR spectrum?

Answer 7

Transmission/ % against wave number/ cm-1
Wave number is the reciprocal of wavelength
The dip in the graph shows an absorbed wavelength

Question 8

What is the fingerprint region.

Answer 8

A region below 1500cm^-1 on an IR spectrum. It allows the identification of a molecule by comparison of spectra.

Question 9

What are there so many identification techniques?

Answer 9

Together, they enable the structure of new compounds to be confirmed.

Question 10

What information does NMR give you?

Answer 10

Information about the position of C13 or H1 atoms in a molecule.

Question 11

Which type of NMR gives a simpler spectra?

Answer 11

C13 NMR giver a simpler spectra than H1 NMR.

Question 12

What does the number of peaks in a C13 spectra tell you?

Answer 12

The number of different carbon environments.

Question 13

What does the chemical shift on an NMR spectrum show you?

Answer 13

The type of molecular environment

Question 14

What reference is used for NMR?

Answer 14

TMS, as all the hydrogens and carbons are in the came environment. So, it gives a small reference peak at 0.

Question 15

What solvent is used in NMR?

Answer 15

CCl4 or CDCl3.
CCl4 is used for non-polar substances
CDCl3 is used for polar substances

Question 16

What does the integration value of a spectra tell you?

Answer 16

It indicates the relative number of H1 atoms in different environments.

Question 17

What does splitting pattern in NMR tell you?

Answer 17

The number of hydrogens in adjacent environments. If the environments are identical, it will give a singlet peak.