INDEX OF HYDROGEN DEFICIENCY NMR SPECTROSCOPY INFRARED SPECTROSCOPY
• provides information about the number of double or triple bonds in a molecule • nuclear magnetic resonance
• the number of hydrogen molecules needed to convert the molecule to the corresponding • used for analysing organic compounds • bonds can vibrate in a number of different ways
started, non-cyclic molecule • atoms with odd mass numbers show signals on NMR spectra and • frequency of vibration occurs in the INFRA-RED REGION
have the property of nuclear spin
formula; IHD = (2x + 2 - y) /2 IR SPECTROSCOPY
• ignore O and S FEATURES OF NMR SPECTRUM • IR spectroscopy: is a technique used to identify compounds based on changes
• counts halogens as hydrogen • shows the intensity of each peak against their chemical shift in vibrations of atoms when they absorb IR of certain frequencies
• add one C and H for every nitrogen in the formula • the area under each peak is proportional to the number of protons • a spectrophotometer
in a particular environment • IR energy absorbed only if a molecule has a permanent dipole that changes as
it berates
MASS SPECTROMETRY • the height of each peak = intensity/absorption from protons
• with symmetrical molecules = IR inactive
CHEMICAL ENVIRONMENT
DETERMINING MOLECULAR MASS
• specific chemical shift ranges • resonance frequency: specific frequency at which the bonds will vibrate, wave
• vaporised molecules are bombarded with a beam of high-speed electrons
number = cm^-1
• these knock off an electron from some of the molecules = molecular ions
INTERPRETING AN NMR SPECTRUM
• relative abundances of detected ions from a mass spectrum: a kind of molecular
• each peak on a NMR spectrum relates to protons in the same • mass spectroscopy + IR spectroscopy = unknown compound
fingerprint that can be identified by computer using a spectral database
environment
• the peak with the highest m/e = the molecular ion = the molecular mass of the compound
• the area under each peak = integration trace - peak ratios FINGERPRINT REGION
• m/z = relative molecular mass of the compound
• below about 1500 cm^-1
• these peaks represent the complex vibrational interactions that occur between
[M+1] PEAK
different bonds within a molecule
• the height of this peak depends on how many carbon atoms are present in the molecule
• members of the series will show the same type of bonds present, but no two
• ex, height of the [M+1] peak for hexane (6 carbons) with be greater than ethane (2
molecules will have the same fingerprint region
carbons)
FRAGMENTATION
• molecular ion peak can be used to identify the molecular mass of a compound
• fragments may appear due to the formation of characteristic fragments or the loss of
small molecules
• ALKANES: are fragmented in mass spectrometry by breaking the C-C bonds
• HALOGENOALKANES: have often multiple peaks around the molecular ion peak
because of the different isotopes of the halogens
• ALCOHOLS: tend to lose a water molecule = rise to peak at 18 below the molecular ion
and m/e 31
• provides information about the number of double or triple bonds in a molecule • nuclear magnetic resonance
• the number of hydrogen molecules needed to convert the molecule to the corresponding • used for analysing organic compounds • bonds can vibrate in a number of different ways
started, non-cyclic molecule • atoms with odd mass numbers show signals on NMR spectra and • frequency of vibration occurs in the INFRA-RED REGION
have the property of nuclear spin
formula; IHD = (2x + 2 - y) /2 IR SPECTROSCOPY
• ignore O and S FEATURES OF NMR SPECTRUM • IR spectroscopy: is a technique used to identify compounds based on changes
• counts halogens as hydrogen • shows the intensity of each peak against their chemical shift in vibrations of atoms when they absorb IR of certain frequencies
• add one C and H for every nitrogen in the formula • the area under each peak is proportional to the number of protons • a spectrophotometer
in a particular environment • IR energy absorbed only if a molecule has a permanent dipole that changes as
it berates
MASS SPECTROMETRY • the height of each peak = intensity/absorption from protons
• with symmetrical molecules = IR inactive
CHEMICAL ENVIRONMENT
DETERMINING MOLECULAR MASS
• specific chemical shift ranges • resonance frequency: specific frequency at which the bonds will vibrate, wave
• vaporised molecules are bombarded with a beam of high-speed electrons
number = cm^-1
• these knock off an electron from some of the molecules = molecular ions
INTERPRETING AN NMR SPECTRUM
• relative abundances of detected ions from a mass spectrum: a kind of molecular
• each peak on a NMR spectrum relates to protons in the same • mass spectroscopy + IR spectroscopy = unknown compound
fingerprint that can be identified by computer using a spectral database
environment
• the peak with the highest m/e = the molecular ion = the molecular mass of the compound
• the area under each peak = integration trace - peak ratios FINGERPRINT REGION
• m/z = relative molecular mass of the compound
• below about 1500 cm^-1
• these peaks represent the complex vibrational interactions that occur between
[M+1] PEAK
different bonds within a molecule
• the height of this peak depends on how many carbon atoms are present in the molecule
• members of the series will show the same type of bonds present, but no two
• ex, height of the [M+1] peak for hexane (6 carbons) with be greater than ethane (2
molecules will have the same fingerprint region
carbons)
FRAGMENTATION
• molecular ion peak can be used to identify the molecular mass of a compound
• fragments may appear due to the formation of characteristic fragments or the loss of
small molecules
• ALKANES: are fragmented in mass spectrometry by breaking the C-C bonds
• HALOGENOALKANES: have often multiple peaks around the molecular ion peak
because of the different isotopes of the halogens
• ALCOHOLS: tend to lose a water molecule = rise to peak at 18 below the molecular ion
and m/e 31
