Exercise 3 Assigning Cracking Patterns of Mass Spectra

Exercise 3 Assigning Cracking Patterns of Mass Spectra C 2 H 5 OH (ethanol) MS m/e fragment ? 46 Parent=P 45 P-H 43 P-2 H P-3 H (? ) 42 + P-CH =CH OH 3 2 31 + CH O 2 30 + C H 2 5 29 + C H 2 4 28 + CH -C 3 27 + CH -C 2 26 +? H O 3 19 + CH 3 15

Exercise 3: mass spectrum fragment assignment (continued) Alfred State College chem 6614 m/e (60) 59 (46) 45 (44) (42) 41 39 31 29 27 26 (15) fragment ID ( ) => weak P =CH 3 C(OH)CH 3 P -H H 2 O-C(CH 3)2 P –CH 3 P –H-CH 3 +C( CH ) 3 2 +H C-C-CH 2 3 + ? ? H 2 O-C-H H 3 C-C-H+ CH 3 C+ CH 2 C+ CH 3+ + Isopropanol EI mass spectrum ASSIGN PEAK ID GIVEN MOLECULAR ID

Exercise 3: mass spectrum fragment assignment (cont. ) Alfred State College chem 6614 Who am I ? ? ? Assume a straight chain alkane (Cn. H 2 n+2) m/e C H 12*n + 1*(2 n+2)=72 14 n+2=72 => n= (72 -2)/14=5 72 P 57 P-CH 3 43 P-C 2 H 5 29 C 2 H 5+ 27 15 =>P=C 5 H 12 Fragment . CH 2 -CH+ (? ) CH 3+

Exercise 3: mass spectrum fragment assignment (cont. ) Alfred State College chem 6614 Who am I ? ? ? Hint: there are two isotopes of Cl at 35 and 37 Try: MW-114 (37 Cl) or 112 (35 Cl) m/e Fragment 114 P with 37 Cl=37 P 112 P with 35 Cl=35 P 77 almost always=>C 6 H 5 fragment 77 C 6 H 5+ (aromatic) 51 50 (37) 37 Cl (35) 35 Cl

Exercise 3: mass spectrum fragment assignment (cont. ) Alfred State College chem 6614 Who am I ? ? ? Try: C 4 H 10 O=> MW =74 With many raw MS, you can attempt rationalizing by subtracting sensible bits (like H, H 2 O, CH 3, C 2 H 5) from the parent, but the remaining fragments must be chemically sensible. m/e 74 57 55 45 44 42 41 31 29 28 27 17 15 Fragment Parent=P P-OH=>4 C chain P-H-H 2 O P-C 2 H 5=+CH 2 -OH CH 2 -O+ P-CH 3 -OH P-CH 3 -H 2 O +CH OH 2 C 2 H 5 + CH 2+ CH 2 CH+ (? ) OH+ CH 3+ => alcohol