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Chemistry Unit 3 > Structural Analysis > Flashcards

Flashcards in Structural Analysis Deck (17):

What does elemental microanalysis determine?

The empirical formula


What are the steps for elemental microanalysis?

Tiny sample is weighed.
Sample is oxidised.
The product mixture is separated by gas chromatography.
The mass of each component is measured using a thermal conductivity detector


Whats the calculation to work out empirical formula?

Divide the percentage by the gram formula mass.


What is mass spectrometry?

A technique used in determining the accurate molecular mass and structural features of an organic compound.


What happens to the unknown organic compound initially when using mass spectrometry?

The unknown compound is vaporised and injected into the mass spectrometer where it is bombarded by high energy electrons


What is the effect of these high energy electrons?

The energy is sufficient to knock electrons out of the molecules and, as a result, they ionise and break into smaller fragments.


What are the positive ions accelerated by and where are they accelerated to?

By a high voltage electric field, into a strong magnetic field.


What is the effect of the magnetic field?

The magnetic field deflects them into a series of separate ion paths according to their mass/charge ratios.


What is the effect of a low mass/charge ratio?

Deflected more by the magnetic field.


What happens to the detected ion paths?

A spectrum is recorded.


What are the two different peaks on the m/z against relative abundance?

Base peak and molecular peak.


What is x-ray crystallography used to do?

Used to determine the precise 3-D structure of an organic compound.


What happens to a selected crystal?

It is exposed to x-rays of a single wavelength


Why does the crystal act as a diffraction grating?

Because the interatomic distances in a compound are approximately equal to the wavelength of the x-rays.


What is the effect of the electrons in the atoms of the organic molecule on the x-rays.

They are scattered, and a diffraction pattern is created.


What can be produced from the diffraction pattern?

Electron density contour maps can be constructed.


Whitman these maps be used to do?

To learn the identity and precise spatial arrangement of each atom in the molecule can be determined. (apart from hydrogen)