Chem 008A , Organic Chemistry, Mass Spectrometry
Mass Spectrometry Problems 1) Calculate the exact mass and average mass for these structures. C Hb C;till(VO ~ – C6Hs Bv- Cb H8 OBr ~-. ~H 14 1 c ,J, o) -t , bt,. o J =Ioo. i’ ‘z..: ,)l 11) ,i” t,) + ‘ 7uJ.OII) -t 1hu,0vS) -t1~-=11l ,’ t /4.ul>l t ,s.11, -=- 1,1 .~17 r : 6u:J.) + t; , -:.1r7 : b u), > -t r c. 1) :. 7 7 ‘ £ +b L’) , ,/4: b(.IJ,011) t J (.I.OJ~) : A~btl1-,0 1′) -t su-1.1JK) 1) .. 1,C1.,).or1)11ll,0VO =- /llV.r;j-lfS ; -t ’11, 10~ -=- 1JE,,1.r ; I I =- 77. /Ob 2) Match each structure to one of the following mass spectra. Explain. 71 ~+ ~g /’..,,’-‘f’ ,~ . ti. M~. @b~Hr00 ·…,_,…Mh @ c CoH”f • + .,, UhCH~lHll,thlH_ ‘)1 • 17. ,. CI-Utth Oh CthOh01; 4J I • Ct-I) Uh C,th. ~NH2 ~-t–r ~,Mh. • C/-t ~J t- t,,1-(,th c-t-1 l =) l.tt’ + -1 l 0 . …._…. 100 .,._,,.., 100 80 80 >-. >-. 1il ·i _§ 60 .§ 60 ., _i;; ., _i;; .2 .2 51 40 &! 40 20 20 0 10 20 1 I 30 40 II 50 m/z 60 70 ‘l 80 ,I 0 10 zo I I,..,,.,…..i-,+ 30 •o 50 m/I 60 70 4-j C. 1-h – u; = Crh. 80 _, 100 .,,._~….,. 100 … 80 so- >- I I ?;-~ § 60 J; < .2: .i; .2: I j 20 60 ., 0:: zo 0 0 10 20 50 30 90 10 100 20 30 s-:, ~lt$-I~ ll 60 70 90 90 60 70 80 90 ,.~…,, 100 80 50 m/z m/z c,). 100 80 70 60 80 : :,; ‘in C § 60 60 ., J; ., .i; Cf • .2: .2: 1 j 11 zo 20 0 0 10 zo 30 50 60 70 10 80 ,…..,..,.,, 100 80 >-. i § 60 ., .i; .2: 0:: 207 0 10 50 m/z 60 70 80 20 30 50 m/z m/z 90 MASS SPECTROMETRY (MS) Exercise 1: Determine the degree of unsaturation (IHD) for the hydrocarbons with the following molecular formulas: (a) C10H16 IO -t I – !!2. :: C'”‘ (b) C1H1NO 7+ I -t 2 – 12. :: s. (c) C8 H9 CIO 8-t- I – 12- = lf I I 2. Exercise 2: An unknown substance shows a molecular ion peak at m/z = 170 with a relative intensity of 100. The M + 1 peak has an intensity of 13.2, and the M + 2 peak has an intensity of 1.00. What is the molecular form4l,a of the unknown? o/. r,,,/i Nrvt.J JJ (~61, ti) ==) /V ,10 M-tl 13. l 1- M-t). /. 00 /o .MAJ /),c, ~/. /r-1~ I~ C An unknown hydrocarbon has a molecular ion peak at m/z = 84, with a relative intensity of 31.3. The M + 1 peak has a relative intensity of 2.06, and the M + 2 peak has a relative intensity of 0.08. What is the molecular formula for this substance? Page 11 Exercise 4: An unknown substance has a molecular ion peak at m/z = 107, with a relative intensity of 100. The relative intensity of the M + 1 peak is 8.00, and the relative intensity of the M + 2 peak is 0.30. What is the molecular formula for this unknown? Exercise 5: The mass spectral data of an unknown liquid are given below. What is the molecul ar formula of this unknown? m/z intensity 78 23.6 0.79 7.55 0.25 79 80 81 (M+} Exercise 6: Propose a molecular formula for each mass spectrum: 100 80 >.. m/z M+ 181 M+ + 1 182 M•+ 2 183 mm 62 5 59 % 100 8.06 95 :-= (/) C Cl) 60 _, .£ Cl) -~ _, 0 Q5 40 (}’.’. 20 o~~~~ ~Tl1IT !lnJm llmlrlT T1ffl1 Tlll’l1′ “‘”‘”””” ‘”‘LI 75 100 125 150 175 m/z Page I 2 ;..;, . • .,1 1:1 100 m/z 112 M• M•+ 1 113 M•+ 2 114 80 ..,>.. ·c;; mm % 53 3.8 0.5 100 40 so 7.2 0.9 C: Cl> 60 …, Cl> -~ …, .2 40 Cl> 20 10 20 30 60 70 80 90 100 110 m/z Exercise 7: the m/z value of the M• peak and of the base Look at the mass spectrum of 2-methylhexane. What is to the large peaks at m/z = 85, 57, and 43. peak? Give possible structures of the fragments giving rise 100 80 >-, _, ‘.. C: Cl) 60 …., .£ Cl) 0 a:; 40 20 0 10 20 30 40 60 50 70 BO 90 100 110 120 m/z Exercise 9: The mass spectra of heptane and 2,2,3-trimethylbutane are given below. Which spectrum represents which compound? Explain. 100 100,. -..,c 80 IO zo zo 0 .,.__, I w zo I I I, m/z 0 .I w I I I zo m/z Page I 4 Exercise 10: Propose a structure for the compound having the following mass spectrum: (a) 100 80 >-, C 2 60 -~ 40 Q) 0 & 20 0 50 40 30 20 10 m/z 100 (b) 80 ….. >-, ‘cii C ….. 60 Q) Q) -~ 0 40 Q) oc 20 0 10 20 30 40 50 60 70 m/z Page I 5
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