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    Mass Spectrometry Part 1

    Lecture Supplement:

    Take one handout from the stage

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    2

    Spectroscopy

    Why bother with spectroscopy?

    Determine structure of unknown substance

    erify purity!identity of known substance

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    3

    SpectroscopyWhat methods are commonly used?

    "#ot rigorously a type of spectroscopy

    Mass spectrometry $MS%"molecular formula

    &nfrared spectroscopy $&'%functional groups

    #uclear magnetic resonance $#M'%

    C/H molecular skeleton

    ()ray crystallography"

    spatial position of atoms

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    Spectroscopy

    *+ample: unidentified white powder

    MS: ,1-.1/#

    &': ben0ene ring secondary amine $'2#.%

    #M': has ,.2),.),.3()ray: not necessary in this case,.3

    ,.3

    #

    .

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    5

    Detector 4uiet

    m!0 too small

    Mass SpectrometryThe Mass Spectrometer

    Fundamental operating principle

    Determine mass by manipulating flight path of an ion in a magnetic field

    sample

    introduction

    Measure ionmass)to)charge ratio

    $m!0%

    Detector

    &oni0ation

    *lectron gun

    5 -

    6cceleratorplates

    Magnet

    m!0 7ust right

    Detector fires

    &oni0ation: ( 5 e) (58 5 2 e)

    m!0 too large

    Detector 4uiet

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    Isotopes

    6ston mass spectrum of neon $1919%#e empirical atomic weight 2-82 amu#e mass spectrum: predict single peak at m!0 2-82

    'esults m!0 relati;e intensity

    2-82 no peak

    2-8- 9-58 5 2 e)

    mass)to)charge ratio $m!0%

    'elati;eionabundance$ + 1% 1@

    , .

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    The Mass Spectrum

    6lternate data presentation888

    m!0 $amu% 'elati;e abundance $ 982

    13 38-

    12 18-

    M52

    M51

    M

    Molecular ion $M%: intact ion of substance being analy0ed

    ragment ion: formed by clea;age of one or more bonds on molecular ions

    12,1.>

    13,1.>or12,2.1.3

    1>,1.>or12,3.1.3or888

    M ) .M ) 2.

    M ) 3.

    M ) >.

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    The Mass SpectrumOrigin of Relative Ion Abundances

    M contributors M51 contributors M52 contributors

    IsotopeNatural

    AbundanceIsotope

    Natural

    AbundanceIsotope

    Natural

    Abundance

    1. 9989A//< 2. -8-1/< 3. ppm

    12, 9A8A93 13, 181-C 1>, ppm

    1># 998@3> 1/# -83@@

    1@E 998C/9 1CE -8-3C 1AE -82->

    19 1--8-

    32S 9/8- 33S -8C@ 3>S >822

    3/,l C/8CC 3C,l 2>823

    C9?r /-8@9 A1?r >9831

    12C& 1--8-

    This table will be provided on an exam. Do not memorize it.

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    The Mass SpectrumRelative Intensity of Molecular Ion ea!s

    &magine a sample containing 1---- methane molecules888

    Molecule F in sample m!0 'elati;e abundance

    12,1.> 9AA9 12 5 $> + 1% 1@ 1--11- 13 5 $> + 1% 1C $11-!9AA9% + 1--< 181

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    Formula from Mass SpectrumM51 ,ontributors

    ,omparing many mass spectra re;eals M51 intensity G181< per , in formula

    *+amples: ,2.@ M 1--

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    Formula from Mass SpectrumM52 ,ontributors

    6nything useful from intensity of M52I

    32S : 3>S

    &sotopes #atural abundances &ntensity M : M52

    1-- : >8>9/8- : >82

    3/,l : 3C,l C/8A : 2>82 1-- : 3189

    C9?r : A1?r /-8C : >983 1-- : 9C82

    ,onclusion:Mass spectra of molecules with S, Cl, or Br have significant M+2 peaks

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    m!0

    'elati;

    eab

    unda

    nc

    e$

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    122'

    elati;eabundance$

    , . ?rM: 3@ 5 C 5 C9 122

    M:M52abundance

    G1:1

    12>

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    Identifying the Molecular Ions

    Which pea!s are molecular ions?

    .ighest m!0 not always MM51 has m!0 one more than m!0 of M

    ?r ,C.C?r

    M: m!0 1C-

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    Formula from Mass Spectrum

    M: 'e;eals mass of molecule composed of lowest mass isotopes

    M51: &ntensity of M51 ! 181< number of carbons

    M52: &ntensity re;eals presence of sulfur chlorine and bromine

    "ummary of Information from Mass "pectrum

    #e+t lecture: procedure for deri;ing formula from mass spectrum

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    Mass Spectrometry Part 2

    Lecture Supplement:

    Take one handout from the stage

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    Summary of Part 1

    "pectroscopy: Study of the interaction of photons and matterJseful to determine molecular structureTypes: MS" &' #M' +)ray crystallography" "not really spectroscopy

    M" fundamental principle: Manipulate flight path of ion in magnetic field,harge $0% magnetic field strength are knownH ion mass $m% is determined

    Isotopes: #atural abundance of isotopes controls relati;e abundance of ions

    Molecular ion #M$ M%&$ M%'$ etc()* &ntact ion of substance being analy0edm!0 of M molecular mass composed of lowest mass isotopes 1. 12, 3/,l etc8

    'elati;e abundance of M51!181< gi;es appro+imate number of carbonsM52 re;eals presence of sulfur chlorine or bromine

    +ragment ion*rom decomposition of molecular ion before reaching detector6nalysis of fragmentation patterns not important for ,hem 1>,

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    Mass Spectrum ormula Structure

    #ot tri;ial to do this directlyStructure comes from formulaH formula comes from mass spectrum

    ,ow do we derive structure from the mass spectrum?

    ?

    ,

    ,.3

    ,l

    ,.3

    .

    ,

    ,.3

    ,l

    ,.3

    . ,3.C,l

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    Mass Spectrum ormula Structure

    ,ow do we derive formula from the mass spectrum?

    m!0 and relati;e intensities of M M51 and M52

    6 few useful rules to narrow the choices

    M: m!0 CA

    ,2.@E3,3.C,l

    ,/.>#

    ,@.@

    etc8

    M

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    .ow Many #itrogen 6tomsI

    ,onsider these molecules:

    #.3 .2##.2

    ormula: #.3 #2.>

    32

    ,C./#3E@

    22C

    ,A.1-#>E2

    19>

    #E2

    ,.3

    E2#

    #E2

    #

    # #

    #

    ,.3E

    E

    .3,

    ,.3

    ,onclusion=hen m!0 $M% e;en number of # in formula is e;en

    1Cm!0 $M%:

    -he Nitrogen RuleK=hen m!0 $M% odd number of # in formula is odd

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    .ow Many #itrogen 6tomsIA Nitrogen Rule ./ample

    M: m!0 CA

    ,2.@E3

    ,3.C,l

    ,/.>#

    ,@.@

    *+ample: ormula choices from pre;ious mass spectrum

    m!0 e;en

    odd nitrogen countdiscarded

    e;en nitrogen count

    e;en nitrogen count

    e;en nitrogen count

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    .ow Many .ydrogen 6tomsI

    ,@.1>max H for 6 C

    Ene pi bond Two pi bonds

    ,onclusion: *ach pi bond reduces ma+ hydrogen count by two

    ,.,

    ,@.12H count max ! 2

    ,@.1-H count max ! "

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    .ow Many .ydrogen 6tomsI

    ,onclusion: *ach ring reduces ma+ hydrogen count by two

    Ene ring Two rings

    ,@.1>max H for 6 C

    ,@.12H count max ! 2

    ,@.1-H count max ! "

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    .ow Many .ydrogen 6tomsIEne nitrogen Two nitrogens

    ,@.1/#

    H count max + #

    ,@.1@#2H count max + 2

    ,onclusion:

    #.2

    #

    #

    ,.3

    ,.3

    #.3,

    ,.3

    ,@.1>max H for 6 C

    #.2 #.2

    *ach nitrogen increases ma+ . count by oneor , carbons and # nitrogens ma+ number of . 2, 5 # 5 2

    -he ,ydrogen Rule

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    Mass Spectrum ormula

    rocedure

    ,hem 1>, atoms: . , # E S ,l ?r &M molecular weight $lowest mass isotopes%

    M51: gi;es carbon countM52: presence of S ,l or ?r#o mass spec indicator for & $ssume a%sent unless otherwise specifie&6ccounts for all atoms e+cept E # and .M= ) mass due to , S ,l ?r and & mass due to E # and .Systematically ;ary E and # to get formula candidatesTrim candidate list with nitrogen rule and hydrogen rule

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    Mass Spectrumormula./ample 0&

    m!0 Molecular ion 'elati;e abundance ,onclusions

    1-2 M 1-- to @8@@ @ or CH @8@C to C8-- C

    " so no S, Cl, or Br

    -x.gen

    Li;eninformation

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    Mass Spectrumormula./ample 0&

    Mass $M% ) mass $, S ,l ?r and &% mass $# E and .%

    1-2 ) ,@ 1-2 ) $@ + 12% 3- amu for # E and .

    E+ygens #itrogens 3- ) E ) # . ormula #otes

    - - 3- ) - ) - 3- ,@.3- iolates hydrogen rule

    1 - 3- ) 1@ ) - 1> ,@.1>E 'easonable

    2 - 3- ) 32 ) - )2 ,@

    .)2

    E2

    #ot possible

    - 2""#itrogen rule

    3- ) - ) 2A 2 ,@.2#2 'easonable

    Ether data $functional groups from &' #M' integration etc8% further trims the list

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    Mass Spectrumormula./ample 0'

    m!0 Molecular ion 'elati;e abundance ,onclusions

    1/C M 1-- 12 ,A.12,l# 'easonable1""#itrogen rule

    Try eight carbons: M ) ,A) ,l 1/C ) $A + 12% ) 3/ 2@ amu for E # and .

    #ot enough amu a;ailable for one o+ygen!one nitrogen or no o+ygen!three nitrogens

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    Mass Spectrumormula./ample 0'

    E+ygens #itrogens 1> ) E ) # . ormula #otes

    - 1> ) - ) 1> - ,9,l# 'easonable1""#itrogen rule

    Try nine carbons: M ) ,9) ,l 1/C ) $9 + 12% ) 3/ 1> amu for E # and .

    #ot enough amu a;ailable for any other combination8

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    ormulaStructure

    What does the formula reveal about molecular structure?

    unctional groups6bsent atoms may eliminate some functional groups

    *+ample: ,C.9# has no o+ygen)containing functional groups

    Pi bonds and rings'ecall from pre;ious: one pi bond or one ring reduces ma+ . count by two*ach two . less than ma+ . count double bond e4ui;alent $D?*%

    &f formula has less than full . count molecule must contain one pi bond or ring

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    ormulaStructure1alculating D2.

    D?* may be calculated from molecular formula:

    Ene D?* one ring or one pi bondTwo D?* two pi bonds two rings or one of eachour D?* possi%leben0ene ring

    D?* , ) .2

    5 5 1#2

    nitrogens

    car%ons

    h.&rogens an& halogens

    D?* , ) $.!2% 5 $#!2% 5 1

    A ) N$1-51%!2O 5 $1!2% 5 1

    3our pi %on&s an&/or ring

    4ossi%le %en5ene ring

    *+ample

    ,A.1-,l#

    >

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    ormulaStructure1ommon Math .rrors

    "mall math errors can have devastating effects3

    No calculators on exams

    6;oid these common spectroscopy problem math errors:Di;ide by 181 di;ide by 18-D?* cannot be a fractionD?* cannot be negati;e

    #e+t lecture: &nfrared spectroscopy part 1