Index Hydrogen Deficiency (IHD) = Degree unsaturation

H H H H H H

׀ ׀ ׀ ׀ ׀ ׀

H - C - C – C – C – C – C – H

׀ ׀ ׀ ׀ ׀ ׀

H H H H H H

H H H H H H

׀ ׀ ׀ ׀ ׀ ׀

H - C - C = C – C – C – C – H

׀ ׀ ׀ ׀

H H H H

H H H H H H

׀ ׀ ׀ ׀ ׀ ׀

H - C - C – C = C – C – C – H

׀ ׀ ׀ ׀

H H H H

Hexane C6H14 IHD = 0

Hex-2-ene C6H12 IHD = 1

Hex-3-ene C6H12 IHD = 1

Cyclohexane C6H12 IHD = 1

How many double bonds/rings present Any double/triple bond/cyclic - number hydrogen atoms decrease

How many H2 need to convert molecule to saturated/non cyclic

Saturated hydrocarbon = CnH2n+2

Saturated IDH = 0

Unsaturated (1 π bond)

2 H deficiency IHD = 1

H H

׀ ׀

C = C

׀ ׀

H H

Unsaturated (2 π bond)

4 H deficiency IHD = 2

Unsaturated (1 ring)

2 H deficiency IHD = 1

Unsaturated (3 π bond) + 1 ring

8 H deficiency IHD = 4

IHD = 1 1 π bond or 1 ring structure

Unsaturated (2 π bond) + 1 ring

6 H deficiency IHD = 3

Unsaturated (4 π bond) + 1 ring

10 H deficiency IHD = 5

IHD = 2 2 π bond / 1 π bond + 1 ring

IHD = 3 3 π bond / 2 π bond + 1 ring / 1 π bond+ 2 ring

Unsaturated (4 π bond) + 1 ring

10 H deficiency IHD = 5

Unsaturated (6 π bond) + 2 ring

16 H deficiency IHD = 8

Click here IHD (Khan Academy)

2

22 yxIHD

H H H H H H

׀ ׀ ׀ ׀ ׀ ׀

H - C - C – C – C – C – C – H

׀ ׀ ׀ ׀ ׀ ׀

H H H H H H

Hexane C6H14 IHD = 0

Hex-2-ene C6H12 IHD = 1

Hex-3-ene C6H12 IHD = 1

Cyclohexane C6H12 IHD = 1

2

22 rsyxIHD

How many double bonds/rings present Any double/triple bond/cyclic - number hydrogen atoms decrease

How many H2 need to convert molecule to saturated/non cyclic

IHD = 1 1 π bond or 1 ring structure

IHD = 2 2 π bond / 1 π bond + 1 ring

IHD = 3 3 π bond / 2 π bond + 1 ring / 1 π bond+ 2 ring

Molecule with C and H Molecule with N, O, S or Halogen

yx HCsrqyx XNOHC

C6H12 C2H2

1

2

)12262(

2

22

IHD

IHD

yxIHD

or

2

2

)2222(

2

22

IHD

IHD

yxIHD

(1 π bond / 1 ring) (2 π bond)

C2H3CI C5H7N

1

2

)13222(

2

22

IHD

IHD

syxIHD

3

2

)17252(

2

22

IHD

IHD

ryxIHD

H - C = C - CI

׀ ׀ H H

(1 π bond) (3 π bond / 2 π bond + 1 ring)

or

H H H H H H

׀ ׀ ׀ ׀ ׀ ׀

H - C - C = C – C – C – C – H

׀ ׀ ׀ ׀

H H H H

H H H H H H

׀ ׀ ׀ ׀ ׀ ׀

H - C - C – C = C – C – C – H

׀ ׀ ׀ ׀

H H H H

H H H H H H

׀ ׀ ׀ ׀ ׀ ׀

H - C - C = C – C – C – C – H

׀ ׀ ׀ ׀

H H H H

Index Hydrogen Deficiency (IHD) = Degree unsaturation Saturated hydrocarbon = CnH2n+2

Molecule Index H2 Deficiency

C2H2 2

Oxygen and Sulfur - No effect on IHD Halogen - like H – CHCI3 = CH4 , C2H5CI = C2H6

Nitrogen – add one to C and one to H - CH5N same IHD as C2H6

Index Hydrogen Deficiency (IHD) = Degree unsaturation

How many double bonds/rings present Any double/triple bond/cyclic - number hydrogen atoms decrease

Molecule with N, O, S or Halogen

srqyx XNOHC

2

22 rsyxIHD

Click here IHD video

1

2

)4222(

2

22

yxIHD

2

2

)2222(

2

22

yxIHD

1

2

)4222(

2

22

yxIHD

0

2

)15222(

2

22

syxIHD

4

2

)6262(

2

22

yxIHD

Molecule Index H2 Deficiency

C2H4 1

Molecule Index H2 Deficiency

C2H4O 1

Molecule Index H2 Deficiency

C2H5CI 0

Molecule Index H2 Deficiency

C6H6 4

Molecule Index H2 Deficiency

C7H6O2 5

5

2

)6272(

2

22

yxIHD

Molecule Index H2 Deficiency

C7H9N2CI3 3

1

2

)19242(

2

22

ryxIHD

Molecule Index H2 Deficiency

C4H9N 1

3

2

)239272(

2

22

rsyxIHD

Molecule Index H2 Deficiency

C6H9NOCI2 2

2

2

)129262(

2

22

rsyxIHD

Molecule Index H2 Deficiency

C4H8CIF 0

0

2

)28242(

2

22

syxIHD

Click here IHD (Khan Academy)

Molecule Index H2 Deficiency

C6H12O6 1

1

2

)12262(

2

22

yxIHD

Halogen

Click here spectroscopy database (NIST)

Weighted average calculation RAM calculation Video on Isotopes Video on weighted average

Relative Atomic Mass

Weighted average mass- due to presence of isotopes

Relative Isotopic Mass, (Ar) of an element: •Relative isotopic mass = Average mass of one atom of element 1/12 x mass of one carbon-12 • Relative isotopic mass, carbon = 12.01

RAM = 12.01 Relative Abundance

13

Why RAM is not a whole number?

Relative Isotopic Mass: = (Mass 12C x % Ab) + (Mass 13C x % Ab) = (12 x 98.9/100) + (13 x 1.07/100) = 12.01

Video on Isotopes

12

Isotopes are present

C C C 12.01

98.9% 1.07%

Click here spectroscopy database (Ohio State)

Mg - 3 Isotopes

24 Mg – (100/127.2) x 100% - 78.6% 25 Mg – (12.8/127.2) x 100% - 10.0% 26 Mg – (14.4/127.2) x 100% - 11.3%

Relative Isotopic Mass: = (Mass 24Mg x % Ab) + (Mass 25Mg x % Ab) + (Mass 26Mg x % Ab) = (24 x 78.6/100) + (25 x 10.0/100) + (26 x 11.3/100) = 24.30

Relative Abundance % Abundance

Pb - 4 Isotopes

204Pb – (0.2/10) x 100% - 2% 206Pb – (2.4/10) x 100% - 24% 207Pb – (2.2/10) x 100% - 22% 208Pb – (5.2/10) x 100% - 52%

Relative Isotopic Mass = (Mass 204Pb x % Ab) + (Mass 206Pb x % Ab) + (Mass 207Pb x % Ab) + (Mass 208Pb x % Ab) = (204 x 2/100) + (206 x 24/100) + (207 x 22/100) + (208 x 52/100) = 207.20

Convert relative abundance to % abundance

Convert relative abundance to % abundance

Relative Abundance % Abundance

Relative Isotopic Mass

24 25 26 24 25 26 Mg Mg

Mass Spectrometer

Uses mass spectrometer

Presence of isotopes and its abundance

Relative atomic mass of an element

Relative Molecular mass of a molecule

Structure of organic compound

Distinguish bet structural isomers

CH3CH2CH2OH OH | CH3CHCH3

CH3 | CH3C-CH3

| CH3

CO2

structural formula

Organic structure determination

24 25 26

Mg Mg

Detail notes from chem msu Click here notes from chemguide

Mass Spectrometer

Parts of Mass Spectrometer

Sample injection

Vaporization Chamber • Sample heat to vapour state

Ionization Chamber • Molecule bombard with electron form positive ion

Accelerator Chamber • M+ ion accelerated by Electric field

Deflector • M+ ion deflected by magnetic field

Detector • Convert amt M+ ion to current. • M+ ion neutralize by electron (more e need - higher current – higher intensity of peak) • Intensity of peak show -relative abundance of ion

Sample X bombard by electron • Form positive M+ ion • Accelerated (Electric Field) • Deflected (Magnetic Field) and Detected X + e- → X+ + 2e-

Vaporization Ionization Accelerator Deflector Detector 3 2 1 5 4

2

1

3 4

5

Click here for simulation

Mass Spectrometer

Parts of Mass Spectrometer

Vaporization Ionization Accelerator Deflector Detector 3 2 1 5 4

Vaporization Injection/ vaporization of sample liquid state gaseous

Ionization Form cation, M+

Acceleration M+ ion accelerate by Electric field

Deflection M+ ion deflect

by magnetic field

Deflection depend: mass/charge (m/z) ratio: (m/z) ratio HIGH↑ - Deflection LOW↓

Deflection depend: mass/charge (m/z) ratio: (m/z) ratio LOW↓- Deflection HIGH ↑

37CI+

35CI+

35CI2+

2

3 4

1

5 Detector • Convert abundance M+ ion to current. • M+ ion neutralize by electron (more e need - high current – high intensity of peak) • Peak Intensity –relative abundance of ion

Video Mass spectrometer Video Ionization/fragmentation Video how MS works

Excellent Online Spectra Database. Click here to view

Mass Spectra Online Database

1 Search methane molecule, CH4

Video on mass spectrometer

Mass/charge m/z

Relative abundance

Isotopic peak M+ + 1 Molecular ion peak, M+

2 Fragmentation pattern CH4 3 Mass Spectrum CH4

Video how MS works

Mg - 3 Isotopes

26 Mg - 11.3% - m/z highest – deflect LEAST 25 Mg - 10.0% 24 Mg – 78.6% - m/z lowest – deflect MOST

Relative Isotopic Mass: = (24Mg x % Ab) + (25Mg x % Ab) + (26Mg x % Ab) = (24 x 78.6/100) + (25 x 10.0/100) + (26 x 11.3/100) = 24.30

Mass spectrometry to determine Relative Isotopic Mass

Deflect MOST

Deflect LEAST

Pb - 4 Isotopes

208Pb – 52% - m/z highest – deflect LEAST 207Pb - 22% 206Pb - 24% 204Pb – 2% - m/z lowest – deflect MOST

Relative Isotopic Mass = (204Pb x % Ab) + (206Pb x % Ab) + (207Pb x % Ab) + (208Pb x % Ab) = (204 x 2/100) + (206 x 24/100) + (207 x 22/100) + (208 x 52/100) = 207.20

Deflect MOST

Deflect LEAST

24 Mg 26 Mg

204Pb 208Pb

CI - 2 Isotopes

37 CI – 24.5% - m/z highest – deflect LEAST 35 CI – 75.5% - m/z lowest – deflect MOST

Relative Isotopic Mass: = (35CI x % Ab) + (37CI x % Ab) = (35 x 75.5/100) + (37 x 24.5/100) = 35.5

Deflect MOST

Deflect LEAST

Br - 2 Isotopes

81Br – 49.3% - m/z highest – deflect LEAST 79Br – 50.6% - m/z lowest – deflect MOST

Deflect MOST

Deflect LEAST

35CI 37CI

Relative Isotopic Mass: = (79Br x % Ab) + (81Br x % Ab) = (79 x 50.6/100) + (81 x 49.3/100) = 79.9

79Br 81Br

Mass spectrometry to determine Relative Isotopic Mass

35 CI 37 CI

79Br 81Br

H - 3 Isotopes

3H – trace amt 2H – 0.015% - m/z highest – deflect LEAST 1H – 99.9% - m/z lowest – deflect MOST

Relative Isotopic Mass: = (1H x % Ab) + (2H x % Ab) = (1 x 99.9/100) + (2 x 0.015/100) = 1.007

Deflect MOST

Deflect LEAST

C - 3 Isotopes

14C- trace amt

13C – 1.1% - m/z highest – deflect LEAST 12C – 98.9% - m/z lowest – deflect MOST

Deflect MOST

Deflect LEAST

1H 2H

Relative Isotopic Mass: = (12C x % Ab) + (813Cx % Ab) = (12 x 98.9/100) + (13 x 1.1/100) = 12.01

12C 13C

3H

14C

Mass spectrometry to determine Relative Isotopic Mass

1H 2H

12C 13C

Ionization and Fragmentation

Ionization forming M+

CH3CH2CH2 : CH3 + e → CH3CH2CH2+.CH3 + 2e

• Fragmentation of M+ producing 43 CH3CH2CH2

+·CH3 → CH3CH2CH2+ + ·CH3

• Fragmentation of M+ producing 15 CH3CH2CH2

+·CH3 → CH3CH2CH2· + +CH3

Ionization and Fragmentation Process- CH3CH2CH2CH3

Ionization Process - CH3CH2CH2CH3 • Bombard by electron form cation • Molecular ion, M+ = 58 • (CH3CH2CH2CH3)+ = 58

Fragmentation Process CH3CH2CH2CH3 • Molecular ion, M+ undergo fragmentation • Cation and Radical form • Cation - Detected • Radical –Not detected (No charged)

H H

׀ ׀ CH3CH2CH2 C:H + e → CH3CH2CH2 C+.H + 2e ׀ ׀ H H

Ionization forming M+

CH3CH2:CH2CH3 + e → CH3CH2+·CH2CH3 + 2e

• Fragmentation of M+ producing 29 CH3CH2

+·CH2CH3 → CH3CH2+ + .CH2CH3

Ionization M+, m/z = 58

CH3CH2CH2CH3 + e → CH3CH2CH2CH3+ + 2e

Ionization and Fragmentation of M+ • Form - m/z = 58, 43 and 15

m/z = 58

m/z = 43

m/z = 15

Ionization and Fragmentation of M+ • Form- m/z = 58 and 29

m/z = 58

m/z = 58

m/z = 29

Unpair electron Positively charged

Will ACCELARATED NOT move

cation radical

CH3CH2CH2CH3

CH3CH2CH2CH3+- 58 - m/z highest –deflect LEAST

CH3CH2CH2+ – 43

CH3CH2+ – 29

CH3+ –15 - m/z lowest– deflect MOST

Ionization/ Fragmentation pattern CH3CH2CH2CH3

Deflect MOST

Deflect LEAST

CH3CH2CH2CH3+

CH3CH2CH2+

ionization

CH3+

Ionization and Fragmentation Process

Fragmentation

Ionization CH3CH2CH2CH3

CH3CH2CH2CH3 + e → CH3CH2CH2CH3+ + 2e → 58

or CH3CH2:CH2CH3 + e → CH3CH2

+·CH2CH3 + 2e → 58

Mass spectrum CH3CH2CH2CH3 Ionization CH3CH2CH2CH3

CH3CH2+

Fragmentation of M+ CH3CH2CH2

+·CH3 → CH3CH2CH2+ - 43

CH3CH2

+·CH2CH3 → CH3CH2+ – 29

CH3CH2CH2

+·CH3 → +CH3 - 15

CH3CH2CH2CH3+- 58

CH3CH2CH2+ – 43

CH3CH2+ – 29

CH3+ – 15

CH3+ CH3CH2CH2CH3

+

CH3CH2CH2OH

CH3CH2CH2OH+- 60 - m/z highest –deflect LEAST CH2CH2OH+ – 45 CH2OH+ - 31 CH3CH2

+ – 29 CH3

+ –15 - m/z lowest– deflect MOST

Ionization/ Fragmentation pattern CH3CH2CH2OH

Deflect MOST Deflect LEAST

CH3CH2CH2OH+

ionization

CH3 +

Fragmentation

Ionization CH3CH2CH2OH

CH3CH2CH2OH + e → CH3CH2CH2OH+ + 2e → 60 or CH3CH2CH2OH + e → CH3CH2

+. CH2OH + 2e → 60

Mass spectrum CH3CH2CH2OH CH3CH2CH2OH

CH3CH2+

Fragmentation of M+ CH3

+.CH2CH2OH → +CH2CH2OH - 45

CH3CH2

+·CH2OH → +CH2OH – 31

CH3CH2

+·CH2OH → CH3CH2+ – 29

CH3

+.CH2CH2OH → +CH3 - 15

CH2CH2OH+ CH2OH+

15 60

CH3CH2CH2OH+- 60 CH2CH2OH+ – 45 CH2OH+ - 31 CH3CH2

+ – 29 CH3

+ – 15

15 60

Ionization and Fragmentation Process

Ionization

CH3+ CH3CH2CH2OH+

CH3CH(CH3)CH2CH3+- 72 - m/z highest –deflect LEAST

CH3CH(CH3)CH2+ – 57

CH3CH(CH3)+ - 43

CH3CH2+ – 29

CH3+ –15 - m/z lowest– deflect MOST

Ionization/ Fragmentation pattern CH3CH(CH3)CH2CH3

Deflect MOST

Deflect LEAST

CH3CH(CH3)CH2CH3+

Ionization

CH3+

Fragmentation

Ionization of CH3CH(CH3)CH2CH3

CH3CH(CH3)CH2CH3 + e → CH3CH(CH3)CH2CH3 + + 2e → 72

or CH3CH(CH3)CH2CH3 + e → CH3CH(CH3)CH2

+.CH3 + 2e → 72 or CH3CH(CH3)CH2CH3 + e → CH3CH(CH3)+.CH2CH3 + 2e → 72

Mass spectrum CH3CH(CH3)CH2CH3 Ionization CH3CH(CH3)CH2CH3

Fragmentation of M+ CH3CH(CH3)CH2

+ - 57 CH3CH(CH3)

+ – 43

CH3CH2+ – 29

CH3+ - 15

CH3CH(CH3)+

15

CH3CH(CH3)CH2+

CH3CH(CH3)CH2CH3+

CH3CH2+

CH3CH(CH3)CH2CH3+- 72

CH3CH(CH3)CH2+ – 57

CH3CH(CH3)+ - 43

CH3CH2+ – 29

CH3+ – 15

Ionization and Fragmentation Process

CH3+ CH3CH(CH3)CH2CH3

+

(C(CH3)4)+ - 72 - m/z highest –deflect LEAST (C(CH3)3)

+ – 57 (C(CH3)2)

+ - 42 (C(CH3))+ – 27 CH3

+ –15 - m/z lowest - deflect MOST

Ionization/ Fragmentation pattern C(CH3)4

Deflect MOST

Deflect LEAST

Ionization

Fragmentation

Ionization of C(CH3)4

C(CH3)4 + e → (C(CH3)4)+ + 2e → 72

Mass spectrum C(CH3)4 Ionization C(CH3)4

(C(CH3)3)+

(C(CH3)4)

(C(CH3)2)+ (C(CH3))+

(C(CH3)4)+ - 72 (C(CH3)3)

+ – 57 (C(CH3)2)

+ - 42 (C(CH3))+ – 27 CH3

+ –15

Fragmentation M+

(C(CH3)3)+ – 57

(C(CH3)2)+ - 42

(C(CH3))+ – 27 CH3

+ –15

Ionization and Fragmentation Process

CH3+ (C(CH3)4)+

CH3

׀

CH3-C-CH3

׀

CH3

Ionization/ Fragmentation pattern CH3(CH2)8CH3

Ionization

Fragmentation

Ionization of CH3(CH2)8CH3

CH3(CH2)8CH3 + e → CH3(CH2)8CH3+ + 2e → 142

Mass spectrum CH3(CH2)8CH3 Ionization

CH3(CH2)8CH3 CH3(CH2)8CH3

+

CH3(CH2)8CH3+ = 142 - m/z highest – deflect LEAST

CH3(CH2)7CH2+ = 127

CH3(CH2)6CH2+ = 113

CH3(CH2)5CH2+ = 99

CH3(CH2)4CH2+ = 85

CH3(CH2)3CH3+ = 71

CH3(CH2)2CH2+ = 57

CH3CH2CH2+ = 43

CH3CH2+ = 29

CH3+ = 15 – m/z lowest – deflect MOST

Loss of methylene gp, CH2 = 14

CH3(CH2)8CH3

CH3(CH2)7CH2+ = 127

CH3(CH2)6CH2+ = 113

CH3(CH2)5CH2+ = 99

CH3(CH2)4CH2+ = 85

CH3(CH2)3CH3+ = 71

CH3(CH2)2CH2+ = 57

CH3CH2CH2+ = 43

CH3CH2+ = 29

CH3+ = 15

Deflect LEAST

CH3+

Deflect

MOST CH3(CH2)8CH3

+

Ionization and Fragmentation Process

15

Ionization/ Fragmentation pattern CH3(CH2)8CH3

Ionization

Fragmentation

Ionization of C6H5CH2OH

C6H5CH2OH + e → C6H5CH2OH+ + 2e → 108

Mass spectrum CH3(CH2)8CH3 Ionization

C6H5CH2OH+ = 108 - m/z highest – deflect LEAST C6H5CH2

+ = 91 C6H5

+ = 77 CH2OH+ = 31 OH+ = 17 – m/z lowest – deflect MOST

C6H5CH2OH C6H5CH2OH+

C6H5CH2OH

C6H5CH2OH+

C6H5CH2+ = 91

C6H5+ = 77

CH2OH+ = 31 OH+ = 17

C6H5CH2OH+ = 108 C6H5CH2

+ = 91 C6H5

+ = 77 CH2OH+ = 31 OH+ = 17

OH+

Deflect

MOST

Deflect LEAST

Ionization and Fragmentation Process

Isomers, Propan-1-ol vs Propan-2-ol

Peak 45 is higher • Loss of methyl radical at both sides produce (CH3CH(OH))+ • No m/z= 29 peak detected – No CH2CH3 found !

Fragmentation peak (M - 15)+ = 45 -> (CH2CH2OH)+

(M - 29)+ = 31 -> (CH2OH)+ (M - 31)+ = 29 -> (CH3CH2)+ (M - 45)+ = 15 -> (CH3)+

Isomers of C3H8OH

Fragmentation peaks (M - 15)+ = 45 -> (CH3CH(OH))+ (M - 17)+ = 43 -> (CH3CHCH3)+ (M - 33)+ = 27 -> (CH3C)+

Vs

Loss of CH3

Loss of CH3CH2

Loss of CH2OH

Loss of CH2CH2OH

Loss CH3

OH OH ׀ ׀ CH3 C+·CH3 → CH3 C

+ + ·CH3

׀ ׀ H H

m/z= 45

CH3CH2CH2OH

OH | CH3CHCH3

Loss OH

Loss OH, CH3, H

Peak 29 and 31 are found • Inductive effect of OH cause splitting of CH3CH2-|-CH2OH • m/z = 29 peak detected – CH2CH3 present

CH3CH2 +· CH2OH → CH3CH2

+ + ·CH2OH

m/z= 29

CH3CH2 +· CH2OH → CH3CH2 ·

+ +CH2OH

m/z= 31

Propan-1-ol Propan-2-ol

15

Vs

Molecular Ion, M+ = 60 -> CH3CH2CH2OH+ Molecular Ion, M+ = 60 -> CH3CH(OH)CH3+

Isomers, 2 methylbutane vs 2, 2 dimethylpropane

CH3

׀ CH3CHCH2CH3

CH3 | CH3C-CH3

| CH3

Peak 29 absent • No CH3CH2 Peak 57 is higher • Loss of methyl radical produce tertiary carbocation • Tertiary carbocation – More stable

Fragmentation peaks (M - 15)+ = 57 -> CH3CH(CH3)CH2

+ (M - 29)+ = 43 -> CH3CH(CH3)

+ (M - 43)+ = 29 -> CH3CH2

+ (M - 57)+ = 15 -> CH3

+

Isomers of C5H12

Fragmentation peaks (M - 15)+ = 57 -> C(CH3)3

+ (M - 30)+ = 42 -> C(CH3)2

+ (M - 45)+ = 27 -> CH3C+ (M - 57)+ = 15 -> CH3

+

Vs

Loss of CH3

Loss of CH3CH2

Loss of CH3CH(CH3)

Loss of CH3CH(CH3)CH2

Loss of CH3

Loss of TWO CH3

Loss of THREE CH3

CH3 ׀ CH3C+·CH3 ׀ CH3

m/z= 57

CH3

׀ CH3 C

+ + ·CH3

׀ CH3

2 methylbutane

2, 2 dimethylpropane

Loss of C(CH3)3

Vs

Peak 29 absent • CH3CH2 present

Molecular Ion, M+ = 72 -> CH3CH(CH3)CH2CH3+ Molecular Ion, M+ = 72 -> C(CH3)4

+

Normal Vs High Resolution Mass spectrometer

Normal Mass Spectrometer

• Molecular formula by adding all RAM

• RMM for molecule = Sum of all RAM • RMM O2 = 16 + 16 = 32 • RMM N2H4 = (14 x 2) + (1 x 4) = 32 • RMM CH3OH = (12 + 3 + 16 + 1) = 32 • Molecular ion peak - O2, N2H4, CH3OH - SAME = 32

RAM, O = 16 RAM, N = 14 RAM, H = 1 RAM, C = 12

High Resolution Mass Spectrometer Measure RMM to 4/5 decimal places

• Molecular formula by adding all RAM • RMM for molecule = Sum of all RAM • RMM O2 = 15.9949 + 15.9949 = 31.9898 • RMM N2H4 = (14.0031 x 2) + (1.0078 x 4) = 32.0375 • RMM CH3OH = (12.0000 )+ (3 x 1.0078) + 15.9949 = 32.0262 • Molecular ion peak- O2, N2H4, CH3OH is the NOT the same

RAM, O = 15.9949 RAM, N = 14.0031 RAM, H = 1.0078 RAM, C = 12.0000

Vs

Vs

O2, N2H4, CH3OH

Same 32

O2 N2H4 CH3OH

different

Video how MS works

High resolution Mass spectrum

37CI+ 35CI+

CI2 molecule

37CI-37CI - 74 - m/z highest – deflect LEAST 35CI-37CI –72 35CI-35CI –70 37CI –37 35CI –35 - m/z lowest– deflect MOST

Ionization/ Fragmentation pattern CI2

Deflect MOST

Deflect LEAST

35CI-35CI+

35CI+

35CI-37CI+

37CI-37CI+

Ionization

37CI+

37CI-37CI+

Fragmentation

Fragmentation of CI2+ into CI+

CI+.CI → [35CI+ + 35CI·] + 2e – 35 CI+.CI → [37CI+ + 37CI·] + 2e –37

Ionization of CI2 to CI2+

CI:CI + e- →[35CI+.35CI] + 2e – 70 CI:CI + e- →[35CI+.37CI] + 2e – 72 CI:CI + e- →[37CI+.37CI] + 2e – 74

m/z = 37

m/z = 35

Ratio (35CI : 37CI) - 3:1

Mass spectrum CI2 / CI atom

Ratio (35CI35CI: 35CI37CI: 37CI37CI) - 9:6:1

Ionization CI2 molecule

37CI-37CI - 74 35CI-37CI – 72 35CI-35CI – 70 37CI – 37 35CI – 35

Ionization and Fragmentation Process

Br2 molecule

81Br-81Br - 162 - m/z highest – deflect LEAST 79Br-81Br –160 79Br-79Br –158 81Br –81 79Br –79 - m/z lowest– deflect MOST

Deflect MOST Deflect LEAST

79Br-79Br+

79Br+

79Br-81Br+

81Br-81Br+

Ionization

81Br+

79Br+

81Br-81Br+

Fragmentation

Fragmentation of Br2+ to Br+

Br+.Br → [81Br+ + 81Br·] – 81 Br+.Br →[79Br+ + 79Br·] – 79

Ionization of Br2 to Br2+

Br:Br + e- →[81Br+.81Br] + 2e – 162 Br:Br + e- →[79Br+.81Br] + 2e – 160 Br:Br + e- →[79Br+.79Br] + 2e – 158

m/z = 79

m/z = 81

Ratio (79Br : 81Br) - 1:1

Mass spectrum Br2 / Br atoms

Ratio (79Br79Br: 79Br81Br: 81Br81Br) – 1:2:1

Ionization Br2 molecule

81Br-81Br - 162 79Br-81Br –160 79Br-79Br –158 81Br – 81 79Br – 79

Ionization/ Fragmentation pattern Br2

Ionization and Fragmentation Process

Ionization/ Fragmentation pattern CH3CH(CI)CH3

Ionization

Ionization

Ionization CH3CH(CI)CH3

CH3CH(CI)CH3+ e → CH3CH(CI)CH3+ + 2e → 78/80

Presence isotope 35CI and 37CI

CH3CH(37CI)CH3+ = 80 - m/z highest – deflect LEAST

CH3CH(35CI)CH3+ = 78

CH3CH(37CI)+ = 65 CH3CH(35CI)+ = 63 CH3CHCH3

+ = 43 CH3C

+ = 27 - m/z lowest – deflect MOST

CH3CH(37CI)+ = 65 CH3CH(35CI)+ = 63 CH3CHCH3

+ = 43 CH3C

+ = 27

CH3CH(CI)CH3 CH3CH(CI)CH3+

CH3CH(CI)CH3+

Isotopic peak (M+)= 78

Isotopic peak (M++2) = 80

CH3CH(35CI)CH3 CH3CH(37CI)CH3

Isotopic peak 63

Isotopic peak 65

CH3CH(35CI)+ CH3CH(37CI)+

CH3CH(CI)CH3 Fragmentation

CH3C+

Deflect MOST Deflect LEAST

Presence M+ and (M++ 2) peak

Presence of Isotopes

Ionization and Fragmentation Process

CH3CH2CH279Br CH3CH2CH2

81Br CH2CH279Br CH2CH2

81Br

Ionization/ Fragmentation pattern CH3CH2CH3Br

Ionization

Ionization

Ionization CH3CH2CH2Br

CH3CH2CH2Br + e → CH3CH2CH2Br+ + 2e → 122/124

Presence isotope 79Br and 81Br

CH3CH2CH281Br+ = 124 - m/z highest – deflect LEAST

CH3CH2CH279Br + = 122

CH2CH281Br+ = 109

CH2CH279Br+ = 107

CH281Br+ = 95

CH279Br+ = 93

CH3CH2CH2+ = 43

CH3C + = 27 - m/z lowest – deflect MOST

Isotopic peak (M+) = 122

Isotopic peak (M++2) = 124

Isotopic peak 107

Isotopic peak 109

Fragmentation

CH3C+

Deflect MOST Deflect LEAST

CH3CH2CH2Br CH3CH2CH2Br+

CH3CH2CH3Br

CH3CH2CH2Br+

CH2CH281Br+ = 109

CH2CH279Br+ = 107

CH281Br+ = 95

CH279Br+ = 93

CH3CH2CH2+ = 43

CH3C + = 27

CH3C+

Deflect

LEAST

CH3CH2CH2Br+

Presence of M+ and (M++ 2) peak

Presence of Isotopes

Deflect

MOST

Ionization and Fragmentation Process

TI

IB Questions on Mass Spectrometer

Mass spectrometer used to investigate isotopic composition of elements. Thallium has two isotopes. 1) State symbol of two singly charged ions form. 2) State which ion will follow path marked X on diagram. lighter -> DEFLECTED MORE 3) Doubly charged ions form. Suggest reason whether they would be deflected less or more than ions at X and Y. DEFLECTED MORE. Cause deflection depends on m/z ratio. Low Mass + High charge -> m/z ratio is low -> deflected more. Naturally occuring boron has 2 isotopes. RAM boron is 10.81.

% abundance x% (100 – x)% Determine percentage abundance of these isotopes. Answer: Let % abundance be x.

1

TI TI 203 205

81 81

X =

B 10 B 11

Relative Isotopic Mass: = (Mass 10B x % Ab) + (Mass 11B x % Ab) = (10 x x/100) + (11 x (100 – x)/100) = 10.81 X = 19%

TI+ 81

203 TI+ 205

81

TI+ 203

81

IB Questions on Mass Spectrometer

Germanium is analysed in mass spec. The first and last processes are vaporization and detection. 1) State the names of other 3 processes in order in which they occur Answer: Ionization -> Acceleration -> Deflection 2) For each of processes named in a (i), outline how process occur Ionization -> Sample bombarded with high energy/high speed electrons Acceleration -> Cations (+ve charged ions) accelerated by an electric field Deflection -> Cations deflected by a magnetic field 3) Germanium found to have following composition i)Define relative atomic mass. Average / weighted masses of all isotopes of an element. ii) Calculate RAM, giving answer to two decimal places.

2

Relative Isotopic Mass = (Mass 70Ge x % Ab) + (Mass 72Ge x % Ab) + (Mass 74Ge x % Ab) + (Mass 76Ge x % Ab) = (70 x 22.60/100) + (72 x 25.45/100) + (74 x 36.73/100) + (76 x 15.22/100) = 72.89

IB Questions on Mass Spectrometer

Shows a mass spectrometer. 1)Identify the parts labelled A, B and C.

2)State and explain which one will undergo greatest deflection. Answer : Greatest deflection -> lowest mass + highest charged -> m/z -> lowest 3) Mass spectrum shown below: i) Explain why there is more than one peak. Existence of isotopes ii) Calculate RAM.

3

Relative Isotopic Mass

= (Mass 24Y x % Ab) + (Mass 25Y x % Ab) + (Mass 26Yx % Ab) = (24 x 79/100) + (25 x 10/100) + (26 x 11/100) = 24.32

• electron gun • ionisation chamber • ionizer

• Electric field • Charged plates • Potential difference

• Magnetic field • Magnet • Electromagnet

greatest deflection – low mass, high charged

smallest deflection – high mass, low charged

A

C

B

Li+

Li2+

7

6

IB Questions on Mass Spectrometer

Vaporized magnesium is introduced into mass spec. One of the ions that reaches detector shown below. 1)Identify number of protons, neutron and electrons Answer : 12 protons, 13 neutrons, 11 electrons

2) State how ion is accelerated in mass spectrometer. Using a strong electric field/strong opposite charged plate/potential difference 3) The ion is also detected by changing the magnetic field. Deduce and explain by reference to m/z values of these two ions of magnesium, which of the ions and is detected using a stronger magnetic field. Answer: - due to lower charge -> m/z is higher -> deflected less -> needs a stronger magnetic field to deflect.

4

Cations (+ve) accelerated by (-ve) plates

25

12

25Mg 2+

smallest deflection – high mass, low charged

Strong magnet/magnetic field to deflect it to bottom

Mg +

25Mg 2+ 25Mg +

25Mg +

25Mg +

Rubidium contains two stable isotopes. RAM for rubidium is 85.47 1)Calculate % of each isotope in rubidium. Answer : Let % abundance be x %.

% Abundance x% (100 – x)%

76.5% 23.5%

2) Vaporized sample is ionized and accelerated. How the use of magnetic field and detector enables percentage of two isotopes to be determined.

5

85 87

Relative Isotopic Mass: = (Mass 85Rb x % Ab) + (Mass 87Rb x % Ab) = (85 x x/100) + (87 x (100 – x)/100) = 85.47 X = 76.5%

Rb

Detector • Convert abundance M+ ions to current. • M+ ions neutralize by electrons (more e needed - higher current – higher intensity of peak) •Ratio of intensity peaks show ratio of ions in sample •Ratio of height of peaks due to 85Rb : 87Rb –> 76.5 : 23.5

Magnetic field/Deflector • M+ ion deflected by magnetic field

- lighter -> deflected more

- heavier -> deflected less

IB Questions on Mass Spectrometer

Rb Rb

85 Rb 87 Rb

85 Rb 87 Rb

85 Rb

87 Rb