Transcript (Concl. Unknowns) IR/UV

Questions of the day:
Which absorptions on an IR spectrum would show you
a) that your unknown is probably a ketone or aldehyde?
b) that your unknown is probably a carboxylic acid?
Today:
• Inert compounds
• IR;
UV
Next time:
Mass spectrometry
“Inert Compounds”
Alkanes
Aromatic Hydrocarbons
(Alkyl halides. Aryl halides.)
Spectroscopy
http://www.chem.ucla.edu/~webspectra/index.html
Infrared Spectroscopy (IR)
• IR region = 4000 - 400 cm-1
(cm-1 unit is the wave number scale and is given by 1/wavelength in
cm) E= h n
• What information do we get from an IR spectrum?
• What is the cause for the typical absorptions?
Fingerprint region
butyl acetate
http://www.chem.ucla.edu/~webspectra/index.html
http://www.chem.ucla.edu/~webspectra/index.html
Aromatics
aromatic
overtones
http://www.chem.ucla.edu/~webspectra/index.html
http://www.chem.ucla.edu/~webspectra/index.html
Alcohols
Gas phase!
Phenol
Ketones
Carboxylic Acids
UV/Visible Spectrophotometry
Which compounds generally absorb in the UV?
CH4? CH3(CH2)10CH3? Ethanol?
Benzene?
Naphtalene? -Carotene? FeCl3?
Which compounds absorb in the visible range?
CH4? CH3(CH2)10CH3? Ethanol?
Benzene?
Naphtalene? -Carotene? FeCl3?
See Chapter in your Lecture text (conjugated systems)
 to *
HOMO to LUMO
A = e x C x l
A = absorbance; e = molar absorptivity
C = concentration in mol/L; l = sample pathlength in cm
UV/Visible Spectrophotometry
lmax
Next time:
• Mass Spectrometry
• MiniQuiz on today’s class
MiniQuiz 8 Problem:
Complete this reaction equation:
OH
NH
O N
NO
2
2
+
NO
2
2