Experimental Determination Of Structure Flashcards
What is carried out to verify the chemical structure of a substance
In organic chemistry a number of experimental techniques are carried out to verify the chemical structure of a substance
What is elemental microanalysis used to determine
Elemental microanalysis is used to determine the masses of C, H, O, S and N in a sample of an organic compound in order to determine it’s empirical formula
What does an empirical formula show
An empirical formula shows the simplest ratio of the elements in a molecule
Elemental microanalysis can be determined from
- combustion product masses
- percentage product by mass
What can be used to determine the accurate GFM and structural features of an organic compound
Mass spectrometry can be used to determine the accurate gram formula mass (GFM) and structural features of an organic compound
Table for calculating empirical formula
Element. C. H. O
%comp.
%/GFM
ans/smallest n
Ratio.
Whole number
In mass spectroscopy what does the peak with the highest mass/charge ratio represent
The peak with the highest mass/charge ratio will usually represent the un-fragmented ionised parent molecule, from which the formula mass of the compound can be determined
Note
This is NOT the highest peak it is the one furthest to the right on the x axis
What does knowing the mass of the parent ion and the elemental analysis allow
Knowing the elemental analysis (what elements are in the compound) and the mass of the parent ion allows the molecular formula for the compound to be determined
Eg hydrocarbon with mass of 58
How many carbons? 4x12 = 48
How many hydrogens? 10 x 1 =10
How can we identify unknown compounds
We can identify unknown compounds by comparing and matching their mass spectrum with mass spectra of known compounds. However care must be taken when a analysing mass spectra as different compounds can have very similar spectra
What is the technique of infrared spectroscopy used for
Infrared (IR) spectroscopy is a technique used to identify functional groups in organic molecules by analysing how they absorb infrared light
What happens when infrared radiation is absorbed by organic compounds
When infrared radiation is absorbed by organic compounds, bonds within the molecule
vibrate (stretch and bend).
What does the wavelength of infrared radiation absorbed depend on
The wavelengths of infrared radiation that are absorbed depend on the type of atoms that make up the bond and the strength of the bond.
X - axis infra-red spectroscopy
Wavenumber (cm-1) - measures frequency of vibration (higher = stronger bonds)
Y- axis in infra-red spectroscopy
Transmittance (%) - how much light passes through the sample (lower transmittance = stronger absorption)
What happens when infrared radiator is passed through a sample of the organic compound
In infrared spectroscopy, infrared radiation is passed through a sample of the organic
compound and then into a detector that measures the intensity of the transmitted radiation at different wavelengths.
Solution triangle
Mg
ppm. Litres
Solid ppm triangle
mg
ppm kg
What is 1ppm
1ppm is 1 part per million
What is 1mg
1mg is 1milligram (1/1000g)
What is 1ppm = to
1ppm = 1mg per litre or 1mg per kg
In mass spectrometry what is bombarded by high energy electron
In mass spectrometry, a small sample of an organic compound is bombarded by
high-energy electrons. This removes electrons from the organic molecule generating
positively charged molecular ions known as parent ions. These molecular ions then break
into smaller positively charged ion fragments.
What is proton nuclear magnetic resonance spectroscopy
Proton nuclear magnetic resonance spectroscopy (proton NMR or 1H NMR) can give information about the different chemical environments of hydrogen atoms (protons or 1H) in an organic molecule, and about how many hydrogen atoms there are in each of these environments.
