4.2.4 Analytical techniques
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what happens to an organic compound when placed in a mass spectrometer
• loses an electron + forms a positive ion, the molecular ion • mass spectrometer detects mass-to-charge ratio of molecular ions which gives molecular mass of compound
how can you find the molecular mass from a mass spectrum
• the molecular ion peak (M+ peak) has to be located > its the clear peak at the highest m/z value on the right-hand side of the mass spec
what is infrared
• heat energy
what happens to a covalent bond when you fire infrared radiation at it
• bond absorbs the IR, making them bend + stretch > each bond vibrates as it absorbs the IR
bonds vibrating from IR can depend on some factor such as:
• bond strength (stronger=faster) • bond length (shorter=faster) • mass of each atom involved in bond (heavy atoms=slower)
in an IR spectrum, what does the height of the peak represent
• the amount of energy absorbed due to bond stretching • lower peak / transmittance = more energy absorbed • lower transmittance = higher absorption
what are wavenumbers above 1500cm-1 used to identify
• functional groups
what are wavenumber below 1500cm-1 used to identify
• used for fingerprinting
how can you differentiate between a C-H and an O-H bond in an IR spec
• peak for OH is more broad
what is elemental analysis
• use of percentage composition data to determine empirical formula