LECTURE 17 FRAGMENTATION MECHANISMS by tek31120

VIEWS: 0 PAGES: 34

									      LECTURE 17
FRAGMENTATION MECHANISMS
    EI - INDUCED
  FRAGMENTATION
WHERE IS THE ODD e- LOCALIZED?

R-R      [R-R]+.
p244
PROBLEM SOLVING
                M+•

FRAGMENT IONS
         PROBLEM SOLVING
                                 M+•

           FRAGMENT IONS




1. Br   2. 73 = C5H13 (R-13:5/8) 3. MS Calc C6H13OBr
        PROBLEM SOLVING
                               M+•

          FRAGMENT IONS




1. Br   2. 73 = C4H9O (+OR,-CH4) 3. MS Calc C6H13OBr
                                            C5H9O2Br
        THREE TYPES OF
       FRAGMENTATIONS
1)  - CLEAVAGE AT ONE BOND
2)  - CLEAVAGE AT TWO BOND OR REARRANGEMENT
3) COMPLEX REARRANGEMENTS
P243
ONE BOND -CLEAVAGE




                  P244
ONE BOND -CLEAVAGE




      MW =45




                      P248
-CLEAVAGE




             P249
P243
TWO BOND -CLEAVAGE




                      P250
                     P251
McLAFFERTY REARRANGEMENT
NO SIMPLE RULE BOOK HERE!

                            P243
ODD EVEN RULE IN FRAGMENTATION




                         P246
ODD EVEN RULE IN FRAGMENTATION




 REMEMBER: EI  [M]+•
                   odd
 soft ESI or CI  [M+H]+
                   even    P246
      OTHER IMPORTANT
           RULES

1. LOSS OF M/Z = 14 NOT POSSIBLE
      [M-CH2]+ OR [F-CH2]+
2. ORDER OF R+ OR R• LOSS 3°>2°>1°>Me>H
      LOSS OF LARGEST ALKYL CHAIN PREFERRED
3. FRAG ION STABILITY>RADICAL FRAG STABILITY

4. LOSS OF “ =• “ NOT FAVORED
USING ALKANES TO REVISIT
FRAGMENTATION MECHANISMS




                     P253
USING ALKANES TO REVISIT
FRAGMENTATION MECHANISMS
            Ref #1 (pp52-54)




                               P253
USING ALKANES TO REVISIT
FRAGMENTATION MECHANISMS




             43 / 57 / 71 / 85 / 99
             C3H7/ C4H9/ C5H11/ C6H13/ C7H15/




                                                P253
          too big 71 & 127
         85 99 113 127


43 / 57 / 71 / 85 / 99 /113 / 127
C3H7/ C4H9/ C5H11/ C6H13/ C7H15/ C8H17 / C9H19




                                        P253
43 / 57 / 71 / 85 / 99
C3H7/ C4H9/ C5H11/ C6H13/ C7H15/




                              P247
43 / 57 / 71 / 85 / 99 /113 / 127
C3H7/ C4H9/ C5H11/ C6H13/ C7H15/ C8H17 / C9H19
PROBLEM SOLVING
                M+•

FRAGMENT IONS
THE MS PLUS NMR DATA



                  M+•=180?&[M-H]+•=179
                  MS: 180 – 79 = 101
                   C5H9O2
                   C6H13O1
                   C7H17

                 NMR 2(CH2)+2(CH2)+CH=
                     C5H9 + O2-3 =
        D   T   T T
                      C5H9BrO2 = 180
                       C5H9BrO3 =196
THE MS PLUS NMR DATA



                     M+•=180?&[M+•]- H=179
                      MS: 180 – 79 = 101
                       C5H9O2
                       C6H13O1
                       C7H17
                    NMR 2(CH2)+2(CH2)+CH=
                        C5H9 + O2-3 =

        D   T   T    T   C5H9BrO2 = 180
                         C5H9BrO3 =196
THE MS PLUS NMR DATA



                     M+•=180?&[M+•]- H=179
                      MS: 180 – 79 = 101
                       C5H9BrO2 UN = 1
                       C6H13O1
                       C7H17
                    NMR 2(CH2)+2(CH2)+CH=
                        C5H9 + O2-3 =

        D   T   T   T    C5H9BrO2 = 180
                         C5H9BrO3 =196
        WORKING STRUCTURES

              FOUR CARBON TYPES
              & D T/T T T




# D’s     2       1        1      2
        WORKING STRUCTURES

              FOUR CARBON TYPES
              & D T/T T T




# D’s     2       1        1      2
WORKING STRUCTURES
    A DECISION
    C2H4Br
    107          M-28
                 -C2H4
             M-43
             -C3H7
WORKING STRUCTURES

    FOUR CARBON TYPES




     [C2H4Br]+• = 107/109
     [C3H5O2 ]+• = 73
              SUMMARY
1. EI fragmentation: EI  [M]+• consider where e-
   is localized.
2. EI fragmentation: EI  [M]+• consider three
   mechanisms
   (a) one bond -clevage,
   (b) two one bond -clevage (RDA)
   (c) complex–McClafferty (featured in Chem
   112)
3. EI fragmentation: EI  [M]+• consider four
   important rules – HTL no loss of 14 by CH2.
4. “MS-calculator” or “Frag-calculator” (MS calc
   pro) needed to interpret the data.
5. EI-MS fragments & NMR great combo for
   problem solving.

								
To top