MASS SPECTRA measure a compound s Mol. Wt. This ionization type is called: electron impact MS

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1 MASS SPECTRA measure a compound s Mol. Wt. p. 213 M + Molecule e - Molecule + 2 e Mole cule + + Mol ecule IONIZATION CHAMBER repellor plate accelerating plates variable field magnet + Mo + lecule Sample inlet (M) + charged particles (e- or other) _ accelerating electric field in vacuum chamber positively charged fragments - degree of deflection based on mass M + This ionization type is called: electron impact MS

2 1 2 r 2 m m e mv eb ev Br 2V 2 2 m/z (or m/e) proportional to 1/V when B is constant and r is constant p. 213 where m = ion mass = ion velocity e (or z) = ion charge V = potential diff. of accelerating plates r = radius of curvature of the path B = magnetic field strength z is normally +1, but sometimes eject 2 electrons, so get M 2+, so get peak at M/2 By changing V slowly, can collect fragments in increasing order of mass

3 A MASS SPECTRUM p base peak = largest peak Fragments M + molecular ion or parent ion m/e Amount of charge (= # ions) received by collector measured for each mass, and plotted as graph of m/e (strictly m/z) vs relative abundance

4 Ionization Methods Electron impact (EI) Chemical ionization (CI) M + from electron beam impact lots of fragmentation M + and M+H + from CH 4 collisions relatively little fragmentation p. 221 Fast atom bombardment (FAB) M + and M+H + from Argon beam collisions low fragmentation Matrix-assisted laser desorption (MALDI) M+H + from matrix protonation Electrospray ionization (ESI) M + or M - but works best if molecule already charged little fragmentation

5 A MASS SPECTRUM p base peak = largest peak Fragments M + molecular ion or parent ion m/e The highest mass peak, corresponds to M + = Molecular Weight of the compound, BUT

6 In nature there are ISOTOPES!!! p. 214 Normal isotopes are: 12 C 1 H 14 N etc. CH 3 NH 2 MW = = 31 However for any molecule that happens to have a 13 C or a 2 H or a 15 N, its MW = 32 and if molecule happens to have a 13 C and a 2 H then its MW = 33 these of course will be seen (BUT ARE SMALL) and are called ISOTOPE PEAKS

7 Nitrobenzene = C 6 H 5 NO 2 = 123 p. 214 and 218 BASE PEAK Molecular Ion, M + ISOTOPE PEAK How large are the isotope peaks?

8 How large are isotope peaks? p. 214 For most elements we use, not very! atom 1 H 12 C 14 N 16 O 19 F 32 S 35 Cl 79 Br M M M C = 1.1%; 2 H = 0.02%; 15 N = 0.4%; 18 O = 0.2%

9 How large are isotope peaks? p. 214 For most elements we use, not very! atom 1 H 12 C 14 N 16 O 19 F 32 S 35 Cl 79 Br M M M C = 1.1%; 2 H = 0.02%; 15 N = 0.4%; 18 O = 0.2% However for some, that is not true: 35 Cl : 37 Cl 79 Br : 81 Br 32 S : 34 S 3 : 1 1 : 1 ~4% this makes chlorides, bromides and sulfides easy to spot

10 Bromides: RBr exists as equal amounts of p. 215 R 79 Br and R 81 Br so MW = [R+79] AND [R+81] we call these M + and M+2 R=CH 3 CH 2 = fragment 3

11 Br n Because of the 1:1 ratio of 79 Br to 81 Br higher bromides show NMR -like patterns i.e. Br 2 = 1:2:1 (M) : (M+2) : (M+4) Br 3 = 1:3:3:1 M, M+2, M+4, M+6 Br 4 = 1:4:6:4:1 etc {CH 2 Br} + eg. CH2Br2 79 Br 81 Br 81 Br 79 Br 79 Br 2 81 Br 2 p. 215 M- 81 Br M- 79 Br 3

12 p. 216 Cl 2 M = 35 Cl 2 = 75% x 75% = 56% M+2 = 35 Cl 37 Cl = 75% x 25% x 2 = 38% M+4 = 37 Cl 2 = 25% x 25% = 6% = 100 : 67 : 11

13 {CH 2 Cl} + p. 216 CH 2 Cl 2 = 100 : 67 : 11 M- 35 Cl 1

14 OTHER ELEMENTS {C,H, N, O} p. 217 In the formula C x H y N z O w Chance of seeing the M+1 and M+2 peaks? 17 O ( M 1) % 11. x y z 0. 04w 18 O ( M 2) % (. 11x) ( y) (. 038z) w M+1 = (# Carbons) x 1.1% Essentially C isotopes are the only ones to worry about here

15 p. 218 Nitrobenzene = C 6 H 5 NO 2 = 123 M+1 = 6 x 1.1% = 7% So, the relative size of M+1 for an organic can be used to establish the # of C

16 Other Elements p. 217 S: M+2 will be 4% of M + S n : M+2 = ~ 4n% F=19 monoisotopic M-19 = fluoride I=127 monoisotopic M-127 = iodide Some elements have lots of isotopes eg. Sn (TIN) has 10! more complex but computable patterns

17

18 Fragmentation patterns (we aren t focusing on this much but it is useful to know some common fragments) p. 219 M-1 H M-43 C 3 H 7 (i-pr) M-15 CH 3 (Me) M-44 CO 2 M-17 OH M-45 CO 2 H M-28 CO M-57 C 4 H 9 (t-bu) M-29 C 2 H 5 (Et) M-77 C 6 H 5 (Ph) M-31 OCH 3 M-91 C 6 H 5 CH 2 (Benzyl) Tropylium cation (6 aromatic)

19 HIGH RESOLUTION MASS SPECTRA p. 221 HRMS instruments can measure accurately to 4 decimal places of mass! Precise masses of some common elements atomic weight isotope mass % relative abundance atomic weight isotope mass % relative abundance H H Si Si H Si C C Si C P P N N S S N S O O S O Cl Cl O Cl F F Br Br Br I I so need to use these values, not integers!

20 12 C= H= N= O= defined p. 221 NO = CH 2 O = N 2 H 2 = CH 2 NH 2 = C 2 H 6 = All of these are mass 30 at low resolution with a HRMS, you essentially analyze which elements are present!

21 at least C 6 X Cl( ) = ( ) p

22 Proton says we have 7H p. 222

23 at least C 6 X X Cl( ) = ( ) Proton: 7H, so therefore we have C 8 H 7 O 2 Cl p. 222

24 C 8 H 7 ClO 2 DBE = {(2x8 + 2)-(7+1)}/2 = 5 = aromatic + 1 p s 155s 135s 130d 110d 56q -CO X benzene = C 6 -OCH 3 }C 8 IR = acid chloride, possibly C=C-O C=O para-benzene 5

25 -OCH 3 p. 222

26 C 8 H 7 ClO 2 DBE = {(2x8 + 2)-(7+1)}/2=5 = aromatic + 1 p s 155s 135s 130d 110d 56q -CO X benzene = C 6 -OCH 3 }C 8 IR = acid chloride, (possibly C=C O C=O ) para-benzene COCl 110 OCH 3 155

27 p. 223 E = F X X = ( ) But from 13 C: >4C, so X and from 1 H have 7H, so X 7 C 8 H 7 O 2 F {(2x8 +2)-(7+1)}/2 = 5 (aro + 1)

28 C 8 H 7 FO 2 p s 133s 130d 129d 126d 89d F-decoupled -COO benzene = C dd 1 6 J=186Hz } C 8 >CHF IR -COOH not conj mono-benzene 10

29 p. 224 CHF COOH H F COOH 3

30 p = 38 = F (18.998) = (4) but at least 4C so C 4 H 5 NOF 2 DBE = {(2x ) (5 + 2)}/2 =2 p

31 p. 225 C 4 H 5 NOF 2 C N >CH- -XCH 2 - Y-CH 2 - } C 4 H 5 N C N 3

32 C 4 H 5 NOF 2 C N >CH- -CH 2 - -CH 2 - all deshielded -F, -F, -O- p. 226 J = 2 J triplet (of t) -CHF 2 (of t) next to CH 2 - J -CH 2 -CHF 2 td 6

33 p. 226 C N -CH 2 -CHF 2 X --O-- --CH OCH 2 - singlet F 2 CH CH 2 O CH 2 CN 2

34 ASSIGNMENT 9

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