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 Absorption Regions 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 N-H CH3 stretch bend 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 sp2 & sp3 C-H stretch 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-pentanone C-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