Mass Spectrometry (see: Chapter 6 of the textbook and Section …chem215/215-216 HH...
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Chem 215-216 HH W11 Lecture Notes (Masato Koreeda) Date: January 10, 2011 Page_1 _of _4 _ Mass Spectrometry (see: Chapter 6 of the textbook and Section 12.3 of Ege’s book) Ionization and possible fragmentation sequences: high-energy electron (10-70 eV) A [A] e e -2 in a high vacuum (10 -6 - 10 -5 torr) ionization molecular ion [B] loss of a neutral molecule radical cation cation [D] loss of an X C fragmentations neutral fragments (not observed) loss of an X loss of a radical E 10 -10 -10 -3 s Those ions in observable. a b c m/z relative ion intensity 100% molecular ion base peak: the strongest peak base peak m: mass z: charge Mass spectrum: Examples of MS spectra – From the way a molecular ion fragments, the structure of a molecule could be deduced. m/z = mass/charge High-resolution MS Application 1 H atomic weight: 1.00783 a peak of m/z = 112 2 H (D) 2.01410 could be, among others: C 6 H 8 O 2 m/z 112.0524 12 C 12.00000 C 7 H 12 O m/z 112.0888 13 C 13.003355 C 7 H 14 N m/z 112.1127 14 N 14.0031 By observing the m/z 112.0523 peak 16 O 15.9949 one can conclude that this peak corresponds to the C 6 H 8 O 2 ion. Isotopes (see p. 2) C 6 H 6 m/z 78 ( 12 C 6 H 6 ); m/z 79 ( mostly, 13 C 12 C 5 H 6 ) The natural abundance of carbon isotopes: 12 C 98.90% and 13 C 1.10%, i.e., roughly 99-100 : 1 So, the peak intensity ratio between m/z 78 and m/z 79 peaks is about 1 : 0.06.
Transcript of Mass Spectrometry (see: Chapter 6 of the textbook and Section …chem215/215-216 HH...
Chem 215-216 HH W11 Lecture Notes (Masato Koreeda) Date: January 10, 2011 Page_1_of _4_ Mass Spectrometry (see: Chapter 6 of the textbook and Section 12.3 of Ege’s book) Ionization and possible fragmentation sequences:
high-energy electron (10-70 eV)
A [A]
e
e-2in a high vacuum
(10-6- 10-5 torr)
ionization
molecularion
[B]loss of a neutral molecule
radical cation cation
[D]
loss of an X C
fragmentations
neutral fragments(not observed)
loss of an X
loss of a radical
E
10-10-10-3 sThose ions in observable.
abcm/z
relativeion
intensity
100%
molecular ion
base peak:the strongestpeak
base peak
m: massz: charge
Mass spectrum:
Examples of MS spectra – From the way a molecular ion fragments, the structure of a molecule could be deduced.
m/z = mass/charge High-resolution MS Application 1H atomic weight: 1.00783 a peak of m/z = 112 2H (D) 2.01410 could be, among others: C6H8O2 m/z 112.0524 12C 12.00000 C7H12O m/z 112.0888 13C 13.003355 C7H14N m/z 112.1127 14N 14.0031 By observing the m/z 112.0523 peak 16O 15.9949 one can conclude that this peak corresponds to the C6H8O2 ion. Isotopes (see p. 2) C6H6 m/z 78 ( 12C6H6 ); m/z 79 ( mostly, 13C12C5H6 ) The natural abundance of carbon isotopes: 12C 98.90% and 13C 1.10%, i.e., roughly 99-100 : 1 So, the peak intensity ratio between m/z 78 and m/z 79 peaks is about 1 : 0.06.
Chem 215-216 HH W11 Lecture Notes (Masato Koreeda) Date: January 10, 2011 Page_2_of _4_
Halogens (Cl and Br) Cl isotopes: 35Cl (75.77%); 37Cl (24.23%) [roughly 3 : 1] Br isotopes: 79 Br (50.69%); 81Br (49.31%) [roughly 1 : 1]
Chem 215-216 HH W11 Lecture Notes (Masato Koreeda) Date: January 10, 2011 Page_3_of _4_
Major Mass Spetral Fragmentation Pathways
Simple cleavages: A1 C C
+•
X
C C•+
A2C
C
+•
C
C•+C
A3C C
+•
C•+CH HHH
+tropylinium ion
rapidisomerization
•A4 + X•
X = halogen, OR, SR, NRR'
B R R'X•
R•X
R'+
CR'R
O•C R• C
O
R'+
α-scission
D
+•
Retro Diels-Alder framentation
+•
+
Rearrangements:E C
H XC
Cn
•C C
Cn + H-X+•
n = 0, 1, 2, 3
CCF C
H
CX
C•
+•
XH
X = O, S, N
G
McLafferty rearrangement
C
CC
C
XH
αβ
γ +•
+•
XH
β
γ
α
X = O, S, NR
Chem 215-216 HH W11 Lecture Notes (Masato Koreeda) Date: January 10, 2011 Page_4_of _4_ MS spectra: examples
