INFRARED SPECTROSCOPY

INFRARED SPECTROSCOPY WWU Chemistry

WWU Chemistry

Infrared Spectrometer WWU Chemistry

Molecular vibrations • IR-Tutor available in CB 280 is great! • Basically two types stretching vibrations bending vibrations WWU Chemistry

IR TUTOR • Select Chemistry Applications icon • Select Structure Drawing icon • Select Spectroscopy icon • Select IR Tutor icon WWU Chemistry

Typical Infrared AbsorptionRegions WWU Chemistry

C-H stretching region • Alkanes C-H sp3 stretch < 3000 cm-1 • Alkenes C-H sp2 stretch > 3000 cm-1 • Alkynes C-H sp stretch ~ 3300 cm-1

C-H bending region • CH2 bending ~ 1460 cm-1 • CH3 bending (asym) appears near the same value • CH3 bending (sym) ~ 1380 cm-1

Hexane CH3 bend CH2 bend C-H stretch WWU Chemistry

How do you think the infrared spectrum of polyethylene would differ from the spectrum of hexane?????

1650 - 1450 cm-1 • The C=C is found at about 1650 cm-1. Monomers would be expected to show the C=C bond, but in polymers the double bond will be absent, unless there is a benzene ring. • The double bonds in a benzene ring are found in the range of about 1600 to 1450 cm-1 WWU Chemistry

1-Hexene sp2 C-H C=C stretch out of plane bendings (oops) sp3 C-H stretch WWU Chemistry

Toluene sp2 C-H sp3 C-H aromatic C=C aromatic oops WWU Chemistry

O-H stretching region • O-H 3300 cm-1 (alcohol). Common polymers with O-H: cellulose and PVA • O-H 3300 cm-1 (acid, broad and ugly). Dicarboxylic acids are monomers. When the carboxylic acid is polymerized with an diol, you get an polyester.

Cyclohexanol bending O-H stretch C-O stretch sp3 C-H stretch WWU Chemistry

Butanoic Acid O-H stretch C=O stretch WWU Chemistry

2250 cm-1 • C≡N 2250 cm-1 The only common polymers with this functional group: polyacrylonitrile and ABS WWU Chemistry

Propanenitrile sp3 C-H C≡N WWU Chemistry

N-H stretching region • 3300 - 3400 cm-1 • –NH2 Primary amines give a pair of peaks. You don’t see primary amines in polymers. • -NH Secondary amines give a single peak The N-H in polyamides and polyurethanes show a very prominent singlet peak!

1-Butanamine N-H bend CH2 CH3 bend N-H stretch doublet sp3 C-H stretch WWU Chemistry

3-Methylbenzenamine sp2 & sp3 C-H N-H stretch Aromatic C=C N-H bend WWU Chemistry

N-Ethylbenzenamine N-H stretch sp2 & sp3 C-H Aromatic C=C WWU Chemistry

1770 - 1670 cm-1 • This is the carbonyl region!! All bands are very strong!! • The following polymers would be expected to show prominent C=O peaks: • Polyesters • Acrylics • Polyamides and polyurethanes • Poly ether ketone (PEEK) WWU Chemistry

C=O Stretching in monomers and polymers WWU Chemistry

2-Butanone sp3 C-H stretch C=O stretch WWU Chemistry

4-Methyl-2-pentanoneC-H < 3000, C=O @ 1715 cm-1 C-H stretch C=O stretch WWU Chemistry

Ethyl Butanoate C-O stretch sp3 C-H C=O stretch WWU Chemistry

Butanoic Acid O-H stretch C=O stretch WWU Chemistry

Propanamide sp3 C-H C=O and N-H stretch (pair) N-H bend WWU Chemistry

Conjugation of C=O with C=C • Conjugation of a carbonyl with a C=C bond shifts values to lower frequencies • For ketones and esters, subtract about 30 cm-1 for conjugation with C=O • Conjugated ketone = 1690 to 1680 cm-1 • Conjugated ester = 1710 to 1700 cm-1 • C=C becomes quite strong!! WWU Chemistry

4-Methyl-3-penten-2-one C-H stretch C=O stretch C=C stretch WWU Chemistry

Acetophenone C-H stretch aromatic C=C conj C=O WWU Chemistry

C-X stretching region • C-Cl 785 to 540 cm-1, often hard to find amongst the fingerprint bands!! • C-Br and C-I appear outside the useful range of infrared spectroscopy. • C-F can be found easily, but aren’t that common - exception! polytetrafluoroethylene WWU Chemistry

Carbon Tetrachloride no C-H! C-Cl stretch WWU Chemistry

INFRARED SPECTROSCOPY