unit 2b: instrumental analysis Flashcards
empirical formula
the simplest whole number ratio of the elements found in the compound
elemental analysis is used to
determine the empirical formula of a compound containing C, H, O, N, and/ or S
elemental analysis
a known mass of the compound is burned in excess oxygen, a mixture of gasses is produced, then the mass of each product gas is determined
mass spectrometry
a technique used to analyse the mass and potential fragments of a molecule, this can tell you about structures within the molecule
parent ion
the peak with the highest m/z, this tells you the gfm of the compound
infrared spectroscopy is used to
identify certain functional groups in a compound
in an IR-spectrometer
IR radiation is passed through a sample of the compound, depending on the types of bonds present and the atoms, different wavelengths of the radiation are absorbed, the detector measures the intensity of radiation absorbed at different wavelengths
the absorbance of infrared radiation is measured in
wave numbers (cm-1)
infrared radiation causes
parts of a molecule to vibrate, there are several different types
different vibrations
absorb different wavelengths of infrared radiation
the wavelength of IR absorbed depends on
the strength of the bond, the type of atoms which are attached to the bond
the fingerprint region
the area below 1500cm-1, it is hard to assign peaks here, everything above this can be assigned to a functional group present
proton NMR
gives us information about the different chemical environments of hydrogen atoms and how many hydrogen atoms are in each of these compounds
NMR uses
radio waves to push the hydrogen atoms to the higher energy state and a detector detects how much energy is released when they relax back down to the low energy stste
the amount of energy released in NMR is affected by
the environment of the hydrogen atoms
absorptions by the sample are measured against
the absorption of a reference substance
the standard reference
TMS, it only has one proton environment and it’s absorption has a chemical shift value of 0 ppm
spectra can be obtained using
low resolution or high resolution H NMR
low resolution H NMR
shows the number of environments that hydrogen is found in, the chemical environment of the hydrogens, and the number of hydrogens at each environment
high resolution H NMR
uses higher radio frequencies than low resolution and produces more detailed spectra, allowing us to tell how many hydrogen neighbours that environment has
doublet
1 H atom on the adjacent C, 2 peaks in spectrum
triplet
2 H atoms in the adjacent C, 3 peaks in spectrum
quartet
3 H atoms in the adjacent C, 4 peaks in spectrum
molecular ion
the highest mass ion
how could you use NMR to differ between chemicals
different number of peaks
relative intensity
the number of H atoms in group
