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 = cm -1 (cm -1 unit is the wave number scale and is given by 1/wavelength in cm) E= h

butyl acetate Fingerprint region

Aromatics aromatic overtones

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? CH 4 ? CH 3 (CH 2 ) 10 CH 3 ? Ethanol? Benzene? Naphtalene?  -Carotene? FeCl 3 ? Which compounds absorb in the visible range? CH 4 ? CH 3 (CH 2 ) 10 CH 3 ? Ethanol? Benzene? Naphtalene?  -Carotene? FeCl 3 ?

UV/Visible Spectrophotometry

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Next time: Mass Spectrometry MiniQuiz on today’s class

Complete this reaction equation: MiniQuiz 8 Problem: NH 2 OH NO 2 2 O 2 N +