IR absorptions

IR absorptions - IR absorptions 1 C-H 2800-3000(aliphatic 2...

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IR absorptions 1. C-H: 2800-3000 (aliphatic) 2. C=C: 1600-1675 3. Alkyne: 2100-2200 4. Carboxcylic acid: broad peaks from 3300-2500 5. Ester (c-o-c) has 2 peaks at 1280 and 1150 6. Carbonyl: 1735-1750 7. Aldehyde: two peaks at 2800 and 2700ish 8. Amines: 3500-3300 9. Acyclic Keytones: 1725-1700 10. Cyclic Keytone: 1780-1745 11. Nitriles (CN)- 2210-2260 IR Carbonyl Frequencies 1750-1735 is saturated aliphatic esters 1740-1720 is sat aliphatic aldehydes 1730-1715 is a,b un sat esters (like benzene ring or double bond with ester) 1715 is sat keytone 1710-1665 is a,b unsat alds/keys (like ald or key with benzene or double bond) 1710 is acetic acid (carb acid) 1735 is methyl acetate (ester with methyl) 1650 is n.n dimethyl acetamide In IR lighter molecules absorb at higher frequencies Para vs Ortho Hydroxyacetophenone Para has a much higher melting point because of the dipole moment which increases bond strength. Because functional groups are opposite from one another they are able to pack in tightly and form crystal lattice structure…the more polar something is the higher the melting point TLC More polar compounds stay at bottom of the plate and less polar are the first to run The more polar the compound the lower the Rf Can increase Rf value by increasing polarity of compound because like dissolves like More poler solvents are stronger eluters Co-spot serves as a reference so you can distinguish between known and unknowns In general compound will move further down the plate with a more polar solvent
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TLC is generally used for determining when reaction has gone to completion, the number of components in a mixture and for checking purity Using silica gel with small particle sizes increases surface area and therefore increases separation Least polar things have highest Rf values Elutropic series (from most to least polar): Water> methanol/ethanol>acetone>ethyl acetate> diethyl ether>methylene chloride>toluene>hexane Can visualize spots on TLC plate via I2 crystals, UV light, color of compound,
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This note was uploaded on 02/07/2009 for the course CHEM 143A taught by Professor Whitesell during the Fall '08 term at UCSD.

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IR absorptions - IR absorptions 1 C-H 2800-3000(aliphatic 2...

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