ir and mass spectroscopy

Question 1

absorption spectroscopy

Answer 1

measures the amount of light absorbed by the sample as a functino of wavelength

Question 2

electromagnetic spectrum lowest energy to highest

Answer 2

radio, microwave, IR, visible, near UV, vacuum UV, X rays, gama rays

Question 3

what does the position of absorption lines in IR spectroscopy tell us

Answer 3

types of functional groups present

Question 4

what does IR spectroscopy measure

Answer 4

vibrational excitation of atoms around bonds that connect then

Question 5

why are not all bonds present in the IR spectrum

Answer 5

only bonds that observe a change in dipole moment during vibration will absorb infrared radiation; have to consider electromagentic field

Question 6

frequency relationship with bond strength

Answer 6

frequency increases when bond gets stronger

Question 7

frequency relationship with atomic mass

Answer 7

frequency increases when heavier

Question 8

how to find number of vibrational modes

Answer 8

3n-6

Question 9

types of vibrational moes

Answer 9

stretching (change bond length)
- symmetric or antisymmetric
bending (change bond angle)
- rocking or scissoring

Question 10

what does electric field do to a polar bond

Answer 10

stretch or compresses it; the force on the + charge is in the direction of the electric field and the force on the - charge is oppostie direction

Question 11

FT IR

Answer 11

sensitive, low energy, takes several scans and averages them

Question 12

what is conjugation

Answer 12

when two double bonds are one bond apart

Question 12

fingerprint region

Answer 12

between 600-1400 cm-1 and has the most complex vibrations

Question 13

how does conjugation affect stretching frequencies

Answer 13

decreases it

Question 14

alkyne

Answer 14

triple bonded c

Question 15

internal alkyne

Answer 15

r - alkyne-r

Question 16

why is the stretching absorption of an internal alkyne weak or absent

Answer 16

there is symmetry

Question 17

stronger , stiffer bonds result from

Answer 17

more s character

Question 18

if c-h bond is an sp2,

Answer 18

it will be just above 3000cm-1

Question 19

if c-h bond is sp3,

Answer 19

it will be just below 3000 cm-1

Question 20

rank bonds from the highest to lowest wave number

Answer 20

3300 - alcohol, amine, amide, alkyne
3000- alkane, alkene, acid
2200 - alkyne, nitrile
1710 - carbonyl
1660- alkene, imine, amide

Question 21

OH and NH stretchuing

Answer 21

both occur at 3300 cm-1

Question 22

how to find degree of unsaturation

Answer 22

u = (2C +2 +N -[h+halogen])/2

Question 23

what does a o-h look like

Answer 23

at 3300 with broad and rounded tip

Question 24

what does secondary amine look like

Answer 24

R2NH
at 3300; broad with one sharp spike

Question 25

what does a primary amine look like

Answer 25

RNH2
broad with two sharp spikes

Question 26

IR spectrum of alcohols

Answer 26

broad stretch at around 3400 (OH stretch)

Question 27

IR spectrum of amines

Answer 27

broad N-H; will have one or two spikes depending on if it is a primary or secondary

Question 28

carbonyl group

Answer 28

c double bond o

Question 29

which group has the strongest IR signal

Answer 29

carbonyl group

Question 30

how are aldehyde c-h bonds different from sp2 c-h bonds

Answer 30

have 2 signals ; at 2700 and 2800

Question 31

types of carbonyl

Answer 31

ketone, aldehyde, carboxylic acid, ester, amide

Question 32

why do strained cyclic ketones absorb at a higher frequency

Answer 32

the angle strain on the carbonyl results in a stronger , stiffer bond

Question 33

how do you tell between a carbon carbon alkyne and carbon nitrogen nitrile

Answer 33

because alkynes have a sp orbital, they have a c-h stretch
nitrile does not have c-h

Question 34

how does mass spectrometry work

Answer 34

high energy beam of electrons breaks the molecule apart; molecule has one unpaired electron and a positive charge; unstable and can lead to more fragmentation

Question 35

what does mass spectrometry result in

Answer 35

radical cation formation

Question 36

where is a molecule most likely going to fragment

Answer 36

between the two most substituted carbons

Question 37

radical cation formation

Answer 37

when a molecule loses one electron, it then has a positive charge and one unpaired electron

Question 38

base peak

Answer 38

tallest peak; abundance are 100%

Question 39

parent peak

Answer 39

peak with highest m/z value and tallest

Question 40

what does it mean when the MW is odd

Answer 40

contains nitrogen atoms

Question 41

what is m/z

Answer 41

mass to charge ratio

Question 42

GCMS ; GC part

Answer 42

gas chromatograph column separates the mixture into compoenets

Question 43

GCMS ; MS part

Answer 43

the mass spectrometer scans mass spectra of the components as they leave the column

Question 44

How to determine isotopes

Answer 44

if the parent peak is at m/z =122, the isotope for the m/z 124 will be m+2

Question 45

how do you know if a bromine is present in mass spectrum

Answer 45

M+ and M+2 should be at 1:1 ratio meaning that the peaks are at similar heights

Question 46

how do you know if a chlorine is present in mass spectrum

Answer 46

M+ and M+2 should have a 3:1 ratio; M+ should be 3x taller

Question 47

common fragments (substituents)

Answer 47

methyl: m/z = 15
ethyl: m/z = 29
keep adding 14 for each carbon lost

Question 48

what kind of carbocations are the most stable on the mass spectra

Answer 48

stable

Question 49

fragmentation for alkenes

Answer 49

most common fragmentation of alkenes is cleavage of an allylic bond to give a resonance stabilized allylic cation; resonance stabillized cations are favored