Chapters 11 and 12:Chapters 11 and 12:IR & NMR Spectroscopy, IR & NMR Spectroscopy,

Identification of UnknownsIdentification of Unknowns

IR SpectroscopyIR Spectroscopy• The presence and also the environment of The presence and also the environment of

functional groups in organic molecule can be functional groups in organic molecule can be identified by infrared (IR) spectroscopy. identified by infrared (IR) spectroscopy.

• Like nuclear magnetic resonance (NMR) and Like nuclear magnetic resonance (NMR) and ultraviolet (UV) spectroscopy, infrared ultraviolet (UV) spectroscopy, infrared spectroscopy is nondestructive. spectroscopy is nondestructive.

• Moreover, the small quantity of sample Moreover, the small quantity of sample needed, the speed with which spectrum can needed, the speed with which spectrum can be obtained, the relatively low cost of the be obtained, the relatively low cost of the spectrometer, and I wide applicability of the spectrometer, and I wide applicability of the method combine to make infrared method combine to make infrared spectroscopy one the most useful tools spectroscopy one the most useful tools available to the organic chemistavailable to the organic chemist

IR SpectumIR Spectum

“Fingerprint” region

• Tables 11.1Tables 11.1 (p. 233) and (p. 233) and 11.211.2 (pp. 238-239) (pp. 238-239) contain characteristic IR peaks of functional contain characteristic IR peaks of functional groups groups

IR Spectra InterpretationIR Spectra Interpretation

• Nuclear magnetic resonance (NMR) spectroscopy is a means Nuclear magnetic resonance (NMR) spectroscopy is a means of determining the number, kind, and relative locations of of determining the number, kind, and relative locations of certain atoms, principally hydrogen and carbon, in certain atoms, principally hydrogen and carbon, in molecules. molecules.

• The number of peaks or groups of coupled peaks indicate The number of peaks or groups of coupled peaks indicate the number of chemically and magnetically distinct the number of chemically and magnetically distinct hydrogen or carbon atoms in a molecule hydrogen or carbon atoms in a molecule

• The The integral integral indicates the relative number of protons within indicates the relative number of protons within a peak or group of peaks. a peak or group of peaks.

• The separation within a group of peaks, called the The separation within a group of peaks, called the coupling coupling constant, J, constant, J, can give information about the locations of the can give information about the locations of the protons relative to other nearby protons and thus, the protons relative to other nearby protons and thus, the geometry of the molecule. geometry of the molecule.

• And the location of a peak in the spectrum is called the And the location of a peak in the spectrum is called the chemical shift chemical shift andand indicates which kind of proton gave rise indicates which kind of proton gave rise to the peak.to the peak.

NMR SpectroscopyNMR Spectroscopy

11H Spectrum ofH Spectrum of Mountain Mountain DewDew

1313C SpectrumC Spectrumofof Mountain Mountain DewDew

• Tables 12.1Tables 12.1 (p. 255) and (p. 255) and 12.312.3 (p. 260) (p. 260) contain H and C chemical shifts contain H and C chemical shifts respectively.respectively.

• Table 12.2 Table 12.2 (p. 256) contains spin-spin (p. 256) contains spin-spin coupling constants.coupling constants.

NMR Spectra InterpretationNMR Spectra Interpretation

Lab ProcedureLab Procedure(students follow own handout)(students follow own handout)

• 1. You will work with a partner1. You will work with a partner• 2. Each person will have an unknown. If there is a 2. Each person will have an unknown. If there is a

group of three there will be three unknowns given to group of three there will be three unknowns given to that group.that group.

• 3.The TA will assign unknowns.3.The TA will assign unknowns.• 4. The NMR spectra of the unknown will be provided 4. The NMR spectra of the unknown will be provided

to you. They are also available on a course web page.to you. They are also available on a course web page.• 5. You will need to do the IR for that unknown.5. You will need to do the IR for that unknown.• 6. The unknown will be either liquid or solid. For liquid 6. The unknown will be either liquid or solid. For liquid

unknowns you will use the silver chloride plates (you unknowns you will use the silver chloride plates (you should have seen this last semester), for solid unknowns should have seen this last semester), for solid unknowns you will need to make a KBr pellet.you will need to make a KBr pellet.