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26 Cards in this Set
- Front
- Back
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_____ is used to determine the molecular weight and the molecular formula of an organic compound, as well as certain structural features.
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Mass Spectrometry
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plot of the relative abundance of each positively charged fragment versus its m/z value.
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Mass Spectrum
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M+1 peak results from molecular ions containing _____.
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13 Carbon
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- value of a molecular ion gives the molecular weight.
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m/z value
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= relative intensity of M+1 peak/ (.011 x (relative intensity of M peak)
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No. of carbons
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____________ is usually small unless the compound has Cl or Br.
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M+2 peak
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__________ determines the exact molecular mass of a fragment with a precision of .0001 amu.
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High-resolution mass spectrometry (HRMS)
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: show M peak and characteristic fragments at m/z = 15 ,29, 43, . . .due to methyl, ethyl, propyl, etc. cations.
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Alkanes
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_____ same relative intensity of M and M+2 peaks. Characteristic fragments: M-79 or (M+2) - 81.
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Alkyl bromides:
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:relative intensity of M+2 peak is one-third that of M. Characteristic fragments: M-35 or M+2 -37 and fragments from alpha cleavage.
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Alkyl chlorides
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: show M peak and fragments from cleavage of C-O bonds from alpha-cleavage.
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Ethers
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: primary and secondary show weak M peak and tertiary show no M peak. M-18 and fragments from alpha cleavage
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Alcohols
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: usually show intense M peak and fragments form alpha-cleavage.
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Ketones
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200-400nm
71-143 kcal per mole Bond Dissociation Energy |
UV
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625-4000
1.8-11 kcal per mole bond deformation (stretch/bend) |
IR
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100-1000nm
10^-5 - 10^-4 kcal/mole Nuclear Spin Flip |
NMR
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Wavelength (UV spectroscopy)
1 nm= Angstrom= m= |
=10
=10^-9 =10^-7 |
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Wavenumber IR spectroscopy
v= |
=cm^-1
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Frequency NMR spectroscopy
v= |
=Hz (s^-1)
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Relationship to Energy
E= |
=hv
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High frequency (v, NMR), Large Wavenumbers(v, IR) and short Wavelength (lamba, UV/Vis) =
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high energy
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is used to determine the kinds of functional groups in an organic compound.
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IR spectroscopy
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(4000-6000) correspond to bond vibrations (streching and bending)
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IR absorptions
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4000-14001/cm: functional group region stretching
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High
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1400-600cm: fingerpint region (bending)
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Low (more energy)
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used to identify organic compounds with conjugated double bonds.
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UV/Vis spectroscopy
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