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Year 1 chemistry as level - Coggle Diagram
Year 1 chemistry as level
Organic analysis
mass spectrometry of organic compounds
When a sample of an
element
passes through a mass spectrometer, the spectrum produced consists of several lines. These lines are due to the different isotopes of the element..
When an organic
compound
passes through a mass spectrometer the spectrum produced also consists of several lines. In this case the lines are due to the original molecule and fragments of the molecule.
The line with the largest m/z ratio is known as the molecular ion. This line has been produced by a molecule which has lost one electron. The lines on the spectrum are due to the molecular ion and ions produced by fragments of the molecule
mass spectra of compounds containing chlorine or bromine
There are two molecular ion peaks in the mass spectra of compounds containing a single chlorine atom. This is because chlorine exists as two isotopes, 35Cl and 37Cl. .
The mass spectrum of 2-chloropropane, CH3CHClCH3.
The peak at m/z ratio 78 is due to the molecular ion [CH3CH35ClCH3]+ containing an atom of 35Cl.
The ratio of the peaks is 3:1. This ratio reflects the abundance of the chlorine isotopes; 35Cl:37Cl 3:1.
The peak at m/z ratio 80 is due to the molecular ion [CH3CH37ClCH3]+ containing an atom of 37Cl.
There are three molecular ion peaks in the mass spectrum of 2,2-dichloropropane
They correspond to [CH3C35Cl35ClCH3]+, [CH3C35Cl37ClCH3]+and [CH3C37Cl37ClCH3]+. The three peaks are in a ratio 9:6:1.
In a molecule containing two chlorine atoms the possible
combinations are:
35Cl and 35Cl
Probability:
¾ × ¾
9/16
Ratio:
9
35Cl and 37Cl or 37Cl and 35Cl
Probability:
(¾ x ¼) + (¼ × ¾)
3/16 + 3/16
Ratio:
6
37Cl and 37Cl
Probability:
¼ × ¼
1/16
Ratio:
1
High resolution mass spectrometry
Measures relative atomic masses to 4 decimal places. A more accurate value of relative molecular mass of the molecular ion can establish which compound is which even if the spectrographs are similar
precise masses of common elements:
1H= 1.0078
16O= 15.9949
14N= 14.0071
12C= 12.0000
Infrared spectroscopy
Pairs of atoms joined by a covalent bond continually vibrate. The frequency of vibration is unique to the atom combination of the bond and differs if the bond is single, double or triple.
A carbon–carbon single bond vibrates at a different frequency to a carbon–carbon double bond or an oxygen– hydrogen bond.
These vibrations have a frequency in the infrared region of the electromagnetic spectrum. This is called the natural frequency of vibration of the bond.
When a beam of infrared radiation is shone onto an organic compound some of the energy is absorbed and the amplitude of vibration of the covalent bond increases.
The bond only absorbs radiation that has the same frequency as the natural frequency of the bond.
Each type of bond has a natural vibration frequency and the same bond surrounded by different groups of atoms has a different natural frequency of vibration.
This knowledge enables chemists to identify groups of atoms in a molecule and the environment surrounding this group.
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Infrared spectra
The spectrum begins at the top of the graph and consists of a series of dips, which represent the infrared frequency absorbed by particular bonds. These dips are given the name ‘peaks’.
An unusual aspect of an infrared spectrum is the scale. The scale is different to the right and left of 2000cm−1. It begins at 4000cm−1 and ends at 500cm−1.
An infrared spectrometer does not contain any glass or quartz because these absorb infrared radiation. All internal reflecting and refracting surfaces are made from polished sodium chloride crystals.
The samples can easily be prepared. The mass of the sample required is very small; approximately 1mg is all that is needed.
