Ch 12 Ppt 2
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__ can be obtained from a very small sample
It does not involve __ or __.
A beam of high-energy electrons __.
The masses of the fragments and their relative abundance reveal information about the __ of the molecule.
- emission of light
breaks the molecule apart
A high-energy electron can do what, creating a what (a positive ion with an unpaired e-).
dislodge an electron from a bond, creating a radical cation
Only the __are deflected by the magnetic field.
Amount of deflection depends on __.
The detector signal is proportional to the __.
By varying the magnetic field, ions of all masses are collected and counted. =>
- number of ions hitting it
The __: A mixture of compounds is separated by __, then identifiedby __.
- gas chromatography
- mass spectrometry
Masses measured to 1 part in 20,000.
A molecule with mass of 44 could be C3H8, C2H4O, CO2, or CN2H4.
If a more exact mass is 44.029, do what?
pick the correct structure from the table
Molecules with heteroatoms
1) __ are present in their usual abundance
2) __ contain 1.1% C-13, so there will be a small __.
3) If Br is present, M+2 is __.
4) If Cl is present, M+2 is __.
- M+1 peak
- equal to M+
- 1/3 M+
If iodine is present, peak at __, __.
If N is present, M+ will be an __.If S is present, M+2 will be __.
- 127, large gap
- odd number
- 4% of M+
More stable carbocations will be __.
Alcohols usually __. M+ may __.
lose a water molecule
not be visible
A compound with no S, Cl, or Br has...
an M+1 peak that is small and an M+2 peak that is even smaller
If sulfur is presnet:
M+2 is 4% M+ (and is larger than M+1)
If Cl is present, what?
M+2 peak is 1/3 as large as the M+ peak
If Bromine is present, what?
M2+ is equal to M+
- recognized by the presence of an iodonium ion, I+ at m/z 127
- This is combined with a characteristic 127-unit gap in the spectrum corresponding to loss of the iodine radical
gives an odd molecular weight, and usually gives some major even-numbered fragments
Stable compounds containing only C, H and O have __ and most __.
- even MW
- of their major fragments are odd-numbered
m/z is hwat? But since what? We do what?
- the mass to charge ratio
- since they''re +1
- we just relate it to its mass
Unlike nitrogen, explain other compounds not containing nitrogen?
give even MW and odd numbered fragments
The stability of the __ is apparently more important than the stability of the __.
True or False:
Both cation and radical are detected.
False: only cation
R-CH2-O-R can be stabilized into what?
loss of an alkyl group
Ketones and aldehydes will be cleaved where?
between the R and the C=O
Ethers will undergo alpha cleavage where?
Amines undergo alpha cleavage to give stabilized cations how?
R2N-CH2 and R
Loss of a small, stable molecule is seen how?
mass spectral peak; indicated by a fragment peak with an even mass number
the radical cation may lose what?
- ethene or other alkenes
When alcohols lose water, what isn't seen and why?
the molecular ion (M+) because it loses water so quickly
In addition to losing water, alcohols commonly fragment next to the __ to give a __. This fragnemntation is called __ because it breaks the bond next to the carbon bearing hte hydroxyl group.
- carbinol cabon atom
- resonance-stabilized carbocation
- alpha cleavage
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