Determination of Structure

Question 1

How are elements often found in organic compounds?

Answer 1

Carbon = CO2
Hydrogen = H2O
Sulfur = SO2
Nitrogen = N2
(Oxygen = as it is)

Question 2

What does elemental analysis allow you to discover?

Answer 2

Empirical Formula

Question 3

What is the Menominee for Empirical Formula?

Answer 3

E very (element)
M an (mass)
G oes (GFM)
N owhere (number = m/GFM)
R unning (ratio = no./smallest)
F ast (formula)

Question 4

How do you work out the mass of an element in a compound?

Answer 4

mass produced
X
elements GFM
————————
compounds GFM

Question 5

What happens in the 4 steps of mass spectrometry?

Answer 5

1. Vaporisation
   - sample heated to gas
   - gas inserted into spectrometer
2. Fragmentation + Ionisation
   - electron gun fires high energy electron at sample
   - some of sample breaks into fragments
   - everything loses 1 electron
3. Acceleration + Deflection
   - repeller (+ charged plate) repels positive fragments etc.
   - half way hit a magnetic field and are deflected
4. Detection
   - fragments land on ion detection plate
   - location indicates deflection and therefore mass

Question 6

What is the highest peak along m/z and what are the rest?

Answer 6

Highest = molecular ion
Rest = fragments

Question 7

Mass spectra + Empirical Formula =

Answer 7

Molecular Formula

Question 8

What must you include if identifying any peaks on the mass spectra?

Answer 8

Positive Charge
[ ]+

Question 9

Where is the peak for a molecular ion with a charge of 2+ found?

Answer 9

Halfway down from molecular ions 1+ m/z

Question 10

What does infrared spectroscopy allow?

Answer 10

Identification of certain functional groups in organic compounds

Question 11

Why do different bonds absorb different wavelengths in the infrared light spectrum?

Answer 11

Because infrared light causes them to bend, stretch or vibrate so different bonds respond differently

Question 12

Where should you look to identify functional groups in infrared spectroscopy?

Answer 12

Page 14 = infrared coloration table

Question 13

What is should you ignore on the infrared spectrum?

Answer 13

Anything below 14,000 cm-1

Question 14

What does NMR low resolution show and how?

Answer 14

It shows hydrogen atom environments as the nucleus of hydrogen atoms can absorb radio waves

Question 15

What do peaks show in NMR low resolution spectra’s and where can you find the relationship between the peak and the Hs environment?

Answer 15

H atom environment

Page 17 of data booklet

Question 16

How can peaks indicate how many hydrogen atoms there are in the compound in NMR low resolution?

Answer 16

Integration of the area under the peak tells us how many hydrogen atoms there are

Question 17

What causes peaks to split in NMR high resolution?

Answer 17

Interaction of neighbouring carbon atoms on the hydrogen is environment

Question 18

What equation works out the number of peaks a peak will be split into?

Answer 18

No. of peaks = n+1

Where n is the number of hydrogen atoms on the neighbouring atom

Question 19

Do you OH and NH groups cause splitting or split themselves?

Answer 19

No

Question 20

In NMR low resolution spectra what is the line on zero and why is it there?

Answer 20

TMS
They are used as standard reference samples
Si(CH3)4