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Published byReynold Simpson Modified over 9 years ago
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Introduction to Spectroscopy Illustrations from R. T. Morrison and R. N. Boyd, Organic Chemistry
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NMR Chemical Shift Chemical Shift ~ measure of local electron density = ( - ref )/ ref * 10 6 ppm
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Peak Integrals 3.8 : 2.9 : 8.8 = 1.31 : 1 : 3.03 = 3.9 : 3 : 9 If formula is known C 11 H 16 : 16 H/15.5 units = 1.03 H per unit
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Correlation Charts
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13 C
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Spin-Spin Splitting Multiplicity : singlet, doublet, triplet, quartet, pentet Determined by number of near neighbors N-Equivalent neighbors: multiplicity = N + 1
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Branched Chains have Characteristic Patterns Quartet-triplet = ethyl Septet-doublet = gem-dimethyl (geminal – attached to same atom)
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Inequivalent Neighbors N-Neighbors: multiplicity = 2 N
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Spin Systems Mutually coupled (or isolated equivalent spins) Two spin systems
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Unknown Double bonds and rings: C c H h O o N n Dbr = (2c-h+n+2)/2 (2*8-10+2)/2 = 4
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Effect of Field Strength Chemical Shift the same in ppm Multiplets have same spacing in Hz 60 MHz: 10 ppm = 600 Hz 1 Hz = 0.0166 ppm 500 MHz: 10 ppm = 5000 Hz 1 Hz = 0.002 ppm
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500 MHz Multiplets simplified (more first order) – Better definition in aromatic region More sensitive (less sample or less time)
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Infrared Spectroscopy Molecular Vibrations Characteristic of functional groups Chain Branching %T
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Aldehydes and Ketones
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Aldehyde RCHO 1725 cm -1 Ketone R 2 CO 1710 cm -1 Cyclobutanones 1780 cm -1 Aromatic ArCHO 1700 cm -1 Aromatic ArCOR 1690 cm -1 Cyclopentanones 1740 cm -1 Conjugated -C=C-CHO 1685 cm -1 -C=C-C=O 1675 cm -1 | | |
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Alcohols
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Carboxylic Acids
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Aliphatic R-COOH 1700-1725 cm -1 Conjugated -C=C-COOH 1680-1700 cm -1 Aromatic Ar-COOH 1680-1700 cm -1
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Carboxylic Acid Derivatives
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Esters R-COOR C=O 1714-1740 cm -1 two bands C-O-R 1050-1300 cm -1
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Ethers
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Phenols
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-CH2-CH2-CH2-CH2- rock 720 cm -1
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