Experimental determination of structure Flashcards
What is elemental microanalysis used for?
Determining the masses of C, H, O, S and N in a sample of organic compound in order to determine its empirical formula.
What is an empirical formula?
Shows the simplest ratio of the elements in a molecule.
Mass spectrometry can be used to determine…
The accurate GFM and structural features of an organic compound.
What happens 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. A mass spectrum is obtained.
The mass-to-charge ratio of the parent ion can be used to determine the … and so …
The GFM of the molecular ions known, and so a molecular formula can be determined using the empirical formula
The peak with the highest m/z value:
- is often the molecular ion (heaviest ion), but it might be too small or undetectable in cases where it is unstable.
- will give the molecular mass and therefore the molecular formula of the compound.
What suggested group has the mass difference of 15?
CH3+
What suggested group has the mass difference of 17?
OH+
What suggested group has the mass difference of 28?
C=O+ or C2H4+
What suggested group has the mass difference of 29?
C2H5+
What suggested group has the mass difference of 31?
CH3O+
What suggested group has the mass difference of 45?
COOH+
What suggested group has the mass difference of 77?
C6H5+
Infrared spectroscopy is used to?
Identify certain functional groups in an organic compound.
What happens when IR is absorbed by organic compounds?
Bonds within the molecule vibrate (stretch and bend)
What does the wavelengths of IR that are absorbed depend on?
The type of atoms that make up the bond and the strength of the bond.
In IR spectroscopy, IR is passed through… and then…
A sample of organic compound and then into a detector that measures the intensity of transmitted radiation at different wavelengths.
The absorbance of IR is measured in? The units are?
Wave numbers, the units are cm-1
The fingerprint region?
Below 1400cm-1, it’s usually used less to identify the groups.
Proton nuclear magnetic resonance spectroscopy can give info about… and about…
The different chemical environments of hydrogen atoms in an organic molecule and about how many hydrogen atoms there are in these environments.
Proton NMR- 1H nuclei behave like…
Tiny magnets and in a strong magnetic field some align with the field (lower energy) whilst the rest align against it (higher energy).
Proton NMR- Absorption of radiation in the radio frequency region of the EM spectrum causes the…
1H nuclei to “flip” from the lower to the higher energy alignment. As they fall back from the higher to the lower energy alignment the emitted radiation is detected and plotted on a spectrum.
In proton NMR the chemical shift is related to… and is measured in ———
The environment of the 1H atom and is measured in ppm.
Integration curves - the area under the peak is related to the number of?
1H atoms in that environment and is often given by an integration curve on a spectrum.
Integration curve- the height of an integration curve is proportional the…
Number of 1H atoms in that environment and so a ratio of 1H atoms in each environment can be determined.
The standard reference substance used in 1H NMR spectroscopy is? Which is assigned a chemical shift value of ——
tetramethylsilane (TMS), zero
1H NMR can be obtained using ————— or ————— NMR
Low resolution or high resolution NMR
High resolution 1H NMR uses? and…
High radio frequencies than those used in low resolution 1H NMR and provides more detailed spectra.
In high resolution 1H NMR an interaction with 1H atoms on the neighbouring carbon atom can result in?
The splitting of peaks into multiples.
What does the number of 1H atoms on the neighbouring carbon determine?
The number of peaks within a multiplet
How can the number of peaks in a multiplet be determined?
Using the n+1 rule, where n is the number of 1H atoms on the neighbouring carbon atom.
