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.)

• What information do we get from an IR spectrum?

• What is the cause for the typical absorptions?

Spectroscopy

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

http://www.chem.ucla.edu/~webspectra/index.html

butyl acetate

Fingerprint region

http://www.chem.ucla.edu/~webspectra/index.html

http://www.chem.ucla.edu/~webspectra/index.html

Aromaticsaromatic overtones

http://www.chem.ucla.edu/~webspectra/index.html

http://www.chem.ucla.edu/~webspectra/index.html

Alcohols

Gas phase!

Phenol

Ketones

Carboxylic Acids

See Chapter in your Lecture text (conjugated systems)

to* HOMO to LUMO

A = x C x l

A = absorbance; = molar absorptivity

C = concentration in mol/L; l = sample pathlength in cm

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?

UV/Visible Spectrophotometry

max

Next time:

• Mass Spectrometry

• MiniQuiz on today’s class

Complete this reaction equation:

MiniQuiz 8 Problem:

NH2

OH

NO2

NO2

O2

N

+