chapter 12 - spectroscopic techniques

Question 1

why analyse substances

Answer 1

• determine purity
• identify structure

Question 2

spectroscopy

Answer 2

electromagnetic spectrum, made up of a range of different wavelengths and therefore energies

Question 3

infrared spectroscopy

Answer 3

• infrared energy absorbed by molecules
• vibrate already vibrating molecules
• different types of vibrations are due to infrared radiation of different frequencies being absorbed
• vibrations change overall dipole

Question 4

factors that affect frequency of radiation absorbed

Answer 4

strength of bonds
- bonds increase = frequency of IR absorbed increases
mass of atoms
- mass increases = frequency decreases

Question 5

mass spectroscopy

Answer 5

determine structure by breaking molecules into fragments in terms of their mass-charge ration (m/z) molar mass
(always positive)

Question 6

nuclear magnetic resonance (NMR) spectroscopy

Answer 6

identify hydrogen arrangement
- no. peaks corresponds to no. environments
- height corresponds to ratio
- position corresponds to chemical shift (table)
slit is n+1

Question 7

13C NMR

Answer 7

identify C environments
- no splitting
- chemical shift is larger than in H NMR

Question 8

determining a structure

Answer 8

1. use % composition to determine empirical formula
2. use mass spec to find molecular formula
3. use IR spec to determine functional groups present
   (keep molecular formula/ mass spec in mind)
4. formulate suspicions
5. use NMR spectra to confirm structure