Mass Spectroscopy

Question 1

Degrees of Unsaturation

Answer 1

hints as to what to expect in regards of binds and structure

Question 2

Equation for Degrees of Unsaturation

Answer 2

(2C + 2 -N - H - X(halogens) ) / 2

Question 3

2 ways to tell degrees of unsaturation

Answer 3

inspection or equation

Question 4

Inspection of Degrees of Unsaturation

Answer 4

ring = 1 unit, double bond = 2 units, and triple bond = 2 units (all other single bonds are saturated)

Question 5

high numbers of unsaturation

Answer 5

chaacterized by benzenes and rings

Question 6

3 things MS is used for

Answer 6

Molecular weight, # of compoents/identity of a mixture, and Isotopic distributions

Question 7

Mass Spec

Answer 7

does not rely on light or ER spectrum; method to determine molecular weight and formula; analyzes masses

Question 8

How MS works

Answer 8

molecule is vaporized and ionized by beam of high energy electrons, later forms a radical cation

Question 9

Molecular/Parent Ion

Answer 9

radical cation [M ^(+.)]

Question 10

Mass of M+

Answer 10

equivalent to weight of entire molecule

Question 11

Why molec ion decomposes?

Answer 11

they are unstable

Question 12

Fragments

Answer 12

radicals and cations with lower MW than molecular ion; formed by single bonds breaking

Question 13

MS graph

Answer 13

plots amount of each cation (relative abundance) on y axis vs its mass on the x axis

Question 14

Fragmentation

Answer 14

Decomposition of a molecular ion into lower molecular weight fragments; patterns can reveal functional groups

Question 15

GC-MS

Answer 15

offers more accurate reading

Question 16

GC in GC-MS

Answer 16

separates mixture and vaporizes sample

Question 17

MS in GC-MS

Answer 17

ionizes sample to form molec ion and lower MW

Question 18

2 ways to get an electron to a fragment

Answer 18

EI or SI ionization

Question 19

EI Ionization

Answer 19

high energy, unstable molec ions, alot of frgament ions

Question 20

SI Ionization

Answer 20

low NRG, stable molec ions, few fragmentations

Question 21

Low resolution MS

Answer 21

measures to whole numbers

Question 22

HIgh resolution MS

Answer 22

measures up to 4 digits

Question 23

M/Z

Answer 23

mass to charge ration; how molec ion and frgaments are separated; charge is usually always +1

Question 24

Minor peaks

Answer 24

show all fragments, including isotopes

Question 25

Parent Peak

Answer 25

peak all the way to the right (M+) and is equivalent to MW of full molecule

Question 26

Base Peak

Answer 26

shows most abudant fragment; take peak and divide by 12 to know amount of carbons and the remainder is the number of Hs; if it seems impossible go down the amount of H for C and up the amount of C for H; molecule minus the halogen; more likely to appear

Question 27

Common M/Zs

Answer 27

methyl = 15, propyl=43, ethyl=29

Question 28

The isotopic difference causes this to be seen well in MS

Answer 28

Halogens

Question 29

M+ VS M+2 ratio

Answer 29

allows you to look for halogens because other atoms don't have isotopic distributions

Question 30

M+1 VS M+3 ratio

Answer 30

allow you to see and compare non halogen atoms

Question 31

alpha cleavage

Answer 31

bond between carbonyl carbon can adjacent carbon; gives neutral radical and resonance stabilized acylium ion

Question 32

these molecules undergo alpha cleavage

Answer 32

aldehydes and ketones

Question 33

dehydration

Answer 33

cleaves 2 bonds to form radical cation and H2O from an alkene

Question 34

this functional group undergoes dehydration

Answer 34

OH

Question 35

loss of OH peak

Answer 35

M-18; mass of 18 units less than molecular ion mass

Question 36

Nitrogen's Rule

Answer 36

Odd M/Z = odd # of N; even M/Z = even # of N

Question 37

Amine's cleavage

Answer 37

breaks the bond between alkyl group and carbon that has amine N

Question 38

Cl peak

Answer 38

M+ VS M+2 peaks in 3:1 ratio

Question 39

Br peak

Answer 39

M+ vs M+2 peaks in 1:1 ratio