13.2 Infrared Spectroscopy of Organic molecules iR region lower energy than visible light(below red-produces heating as with a heat lamp) 2.5×106mto25×105 m region used by organic chemists for structural analysis iR energy in a spectrum is usually measured as wavenumber(cm- ), the inverse of wavelength and proportional to frequency pecific IR absorbed by organic molecule related o Its structure
13.2 Infrared Spectroscopy of Organic Molecules • IR region lower energy than visible light (below red – produces heating as with a heat lamp) • 2.5 ´ 10-6 m to 2.5 ´ 10-5 m region used by organic chemists for structural analysis • IR energy in a spectrum is usually measured as wavenumber (cm-1), the inverse of wavelength and proportional to frequency • Specific IR absorbed by organic molecule related to its structure
Ultraviolet Visible Near Infrared Far infrared Microwaves infrared 10-5 10 10 10 (cm) A=2.5×10-4cm A=25×10-3cm =2.5m =25m =4000cm =400cm-1 Energy 92004 Thomson/ Brooks Cole
Infrared Energy Modes IR energy absorption corresponds to specific modes, corresponding to combinations of atomic movements, such as bending and stretching of bonds between groups of atoms called"normal modes Energy is characteristic of the atoms in the group and their bonding Corresponds to vibrations and rotations Symmetric Antisymmetric In-plane Out-of-plane stretching Thomson· Brook
Infrared Energy Modes • IR energy absorption corresponds to specific modes, corresponding to combinations of atomic movements, such as bending and stretching of bonds between groups of atoms called “normal modes” • Energy is characteristic of the atoms in the group and their bonding • Corresponds to vibrations and rotations
Interpreting Infrared Spectra Most functional groups absorb at about the same energy and intensity independent of the molecule they are in Characteristic higher energy ir absorptions can be used to confirm the existence of the presence of a functional group in a molecule IR pectrum has lower energy region characteristic of molecule as a whole fingerprint region) See samples in Figure 12-13
Interpreting Infrared Spectra • Most functional groups absorb at about the same energy and intensity independent of the molecule they are in • Characteristic higher energy IR absorptions can be used to confirm the existence of the presence of a functional group in a molecule • IR spectrum has lower energy region characteristic of molecule as a whole (“fingerprint” region) • See samples in Figure 12-13
Regions of the Infrared Spectrum 40002500cm1NH,C-·20001500cm- double H, O-H(stretching) bonds(stretching) 3300-3600N-H.O-H C=01680-1750 30C-H C=C1640-1680cm 2500-2000 cm-l CoC and Below 1500 cm-l C°N( stretching) Ingerprint region Wavelength (um) 2.5 678910 121416 N一H C=0 C≡N C=N Fingerprint regi C≡C 40003500300026002200200018001600140012001000 Wavenumber (cm-l) cHone· Broo cale
Regions of the Infrared Spectrum • 4000-2500 cm-1 N-H, CH, O-H (stretching) – 3300-3600 N-H, O-H – 3000 C-H • 2500-2000 cm-1 CºC and C º N (stretching) • 2000-1500 cm-1 double bonds (stretching) – C=O 1680-1750 – C=C 1640-1680 cm-1 • Below 1500 cm-1 “fingerprint” region