PowerPoint Presentation
CHM2120 3XOrganic chemistry II
SpectroscopyInfrared spectroscopy11What is in that white
powder?2Elemental analysisUsed to find the empirical formulaMass
spectroscopyUsed to identify the molecular weightDegrees of
unsaturationIdentify number of double bonds , triple bonds, and
ringsInfrared spectroscopy (IR)Used to identify functional groups
(alcohols, alkenes, ketones, etc.)Nuclear magnetic resonance (NMR)
spectroscopy Analysis results in precise determination of molecular
structure
*Apply these in order when given an unknown compoundDegrees of
unsaturation3DU = (2C + 2 + N H X) / 2Ignore O and S
Infrared spectroscopy4
Each type of bond (C-H, C-O, C=C, etc.) vibrates at a specific
frequency ( = c / )
Infrared spectroscopy5
In IR spec, we like to report in wavenumbers (cm-1)Wavenumber =
1 / 6Infrared spectroscopyKey Absorptions (cm-1)
Functional groupBondWavenumberPeak shapealkyl, sp3C H2850 2960m,
sharpalkene, sp2C=C H just >3000m, sharpC=C1640 - 1680m,
sharpAlcoholRO H 3200 3650s, broad Carboxylic acidR(C=O)O-H2500
3300s, broad AmineR2N-H3300 3500 s, broad CarbonylR2C=O1650 1780 s,
sharpNitrileRCN2220 2260 v, sharpAlkynylCC-H~3300m, sharpCC2100 -
2260v, sharpIn IR spec, we like to report in wavenumbers
(cm-1)Wavenumber = 1 / 7Infrared spectroscopy
8Identify the key absorptions
9Identify the key absorptions
10Identify the key absorptions
11Identify the key absorptions
12Identify the key absorptions
13Identify the key absorptions
14Identify the key absorptions
15Practice problem
Desired reactionDid we make the product we wanted? What
happened?
IR of product
