Spectroscopy/spectrometry

Question 1

spectroscopy

Answer 1

study of how a compound responds to light

Question 2

spectrum

Answer 2

graph of frequency vs absorption, emission, or some other response

Question 3

steps in mass spectrometry

Answer 3

1. put charge on sample
2. send molecular ions through magnetic field
3. heavier ions will be deflected less

Question 4

mass spectrum

Answer 4

• shows abundance of ions in mass-to-charge ratio!
• base peak: max. height peak, often the molecular weight of your molecule

Question 5

fragmentation

Answer 5

• hitting sample with high intensity electrons to put a charge on it causes many molecules to fragment
• helpful for detecting parts of molecular structure!

Question 6

degrees of unsaturation

Answer 6

• how many multiple bonds or rings are in a molecule

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

Question 7

what does IR spectroscopy tell us?

Answer 7

• certain IR frequencies cause bonds to vibrate, bend, or stretch
• stronger bonds need higher frequencies (higher energy)
• IR gives info on functional groups, NOT exact structure!

Question 8

general regions in IR spectra

Answer 8

• > 2700: OH, NH, and CH single bond stretches
• 2000-3000: CC and CN triple bond stretches
• 1500-2000: CC, CN, and CO double bond stretches
• <1500: fingerprint region (unimportant)

Question 9

UV-vis spectroscopy

Answer 9

• highly conjugated systems absorb UV or visible light due to smaller HOMO-LUMO gaps
• alkanes don’t absorb well
• dye molecules often have huge delocalization (absorb visible light!)

Question 10

UV-vis spectroscopy uses in ochem

Answer 10

• used for thin layer chromatography (TLC)
• different compounds will separate at different speeds depending on polarity!

Question 11

IR spectroscopy groups to know

Answer 11

• carbonyl: 1700
• OH: strong broad peak >3000, generally carboxylic acid if it goes under 3000
• amine: 3300-3500ish
• CH bonds: <3000 for sp3, >3000 if also sp2