6.3.2 Spectroscopy

Question 1

NMR spectroscopy

Answer 1

involves interaction of material with low energy radiowave region of the electromagnetic spectrum
uses the same technology as MRI to obtain diagnostic information about internal structure in body scanners

Question 2

2 types of NMR

Answer 2

Carbon-23 NMR

Proton NMR

Question 3

in a carbon 13 spectra what is there one single peak for

Answer 3

each set of equivalent carbon atoms

Question 4

in carbon 13 nmr when do you have different peaks `

Answer 4

when each carbon is bonded to a different group

label them C a,b,c,d

Question 5

in a H NMR spectrum what is there one signal for

Answer 5

each set of equivalent H atoms

Question 6

what else is shown on the H peaks in proton NMR

Answer 6

the intensity of the peaks (integration values)

proportional to the number of equivalent H atoms it represents

Question 7

solvents

Answer 7

samples are dissolved in solvents with no H atoms
so that the H NMR there will be no peaks from the solvent
same solvent used in C 13 NMR however it is a known peak so can be ignored

Question 8

examples of solvents used

Answer 8

CCl4

CDCl3

Question 9

good solvent for non-polar organic molecules

Answer 9

CCl4 as it is a non-polar compound

Question 10

good solvent for polar organic molecules

Answer 10

CDCl3 as it is a polar covalent compound

Question 11

which calibration compound is used in H and C13 spectra

Answer 11

TMS

tetramethylsilane

Question 12

why is TMS used to calibrate the spectrum

Answer 12

signal is away from all of the others
only gives one signal
strong signal so a small amount is needed
non-toxic
inert
low boiling point so can be easily removed

Question 13

what is the scale called that the spectra are recorded on?

Answer 13

chemical shift
how much the field has shifted from the field for TMS
measured in ppm
relative scale of how far the frequency of the proton signal has shifted from that for TMS

Question 14

what does the chemical shift of a H NMR depend on

Answer 14

which other atoms or groups are near the H

more electronegative give a greater shift

Question 15

proton exchange using D2O

Answer 15

then a process of proton exchange happens with the H in any OH and NH bonds
has the effect of removing the peaks from the H NMR spectra
can help with the identification of OH and NH peaks on the spectra

Question 16

if the carbons are in the same range what is it not possible to identify in C13 NMR

Answer 16

the exact carbon corresponding to each peak

Question 17

in high resolution H NMR what can happen to each signal

Answer 17

can be split into further lines

due to equivalent H’s on neighbouring C atoms

Question 18

splitting of peak is equal to

Answer 18

the number of inequivalent H’s on neighbouring C atoms +1

Question 19

singlet:
appearance 
split number of peaks 
number of neighbouring inequivalent H atoms 
relative size

Answer 19

1 peak drawn straight up
1 peak
0 inequivalent H

Question 20

doublet:
appearance 
split number of peaks 
number of neighbouring inequivalent H atoms 
relative size

Answer 20

2 peaks straight up
2 split peaks
1 neighbouring inequivalent H
1:1

Question 21

triplet: 
appearance 
split number of peaks 
number of neighbouring inequivalent H atoms 
relative size

Answer 21

3 peaks, 1st and 3rd same size and 2nd is taller
3 split peaks
2 neighbouring inequivalent H atoms
1:2:1

Question 22

quartet: 
appearance 
split number of peaks 
number of neighbouring inequivalent H atoms 
relative size `

Answer 22

4 peaks, 1st and 4th the same size and are smaller, 2nd and 3rd are taller and the same size
4 split peaks
3 neighbouring inequivalent H atoms
1:3:3:1

Question 23

quintet:
appearance 
split number of peaks 
number of neighbouring inequivalent H atoms 
relative size

Answer 23

1st and last small and same size, 2nd and 4th taller and same size, 3rd is tallest
5 split peaks
4 neighbouring inequivalent H atoms
1:4:6:4:1

Question 24

what do H bonded to N or O do on an NMR spectra

Answer 24

do not couple with other protons and appear as singlets

Question 25

what is the region below 1500 on an IR spec called

Answer 25

fingerprinting region

Question 26

peak of carboxylic acid compared to alcohol

Answer 26

broad OH peak in carboxylic acid

Question 27

how do modern breathalysers work

Answer 27

measure ethanol in the breath by analysis using IR spectroscopy

Question 28

what is the peak with largest m/z value in mass spectrum due to

Answer 28

the complete molecule
equal to mr of the molecule
called the parent ion or the molecular ion

Question 29

molecular ion formation

Answer 29

M -> [M]+ + e-
loses an electron and becomes both an ion and a free radical
ion is responsible for the peak

Question 30

what are molecular ion fragments dueto

Answer 30

covalent bonds breaking

Question 31

more stable the ion then what in mass spec

Answer 31

greater the peak intensity

Question 32

peak with the highest m/z ratio

Answer 32

molecular ion

charge of the ion is 1+ the m/z ration is equal to the mr

Question 33

using the molecular ion peak from the mass spec to calculate molecular formula

Answer 33

find the molecular ion peak

empirical formula, divide to find correct ratio

Question 34

how to tell on an IR spec if a compound is an ester

Answer 34

C=O but no O-H

Question 35

using NMR to give details of carbon chains

Answer 35

4 peaks= 4 different environments

count the number of split peaks to find out the neighbouring inequivalent