Learning Guide for Chapter 3 - Infrared SpectroscopyI. Introduction to spectroscopy - p 1II. Molecular vibrations - p 3III. Identifying functional groups - p 6IV. Interpreting an IR spectrum - p 12I. Introduction to spectroscopyWhat does it mean to characterize a compound?What are some examples of when you would need to do this?What are some physical properties of organic compounds, and how can they be used in characterization?How are chemical tests used to characterize organic compounds?What does spectroscopy use to characterize a compound?What are the most common kinds of spectroscopy used in organic chemistry, and what kinds of information do they give?Characterizing compoundsLG Ch 3 p 2What kinds of light are present in the electromagnetic spectrum? How do they affect atoms and molecules?low energyhigh energyWhat unit of frequency is used in IR spectroscopy? What is the range of frequencies used in IR spectroscopy?What are the essential components of an IR spectrometer?What is FTIR?How can you take the IR of a liquid compound?How can you take an IR of a solid compound?The Electromagnetic SpectrumThe IR Spectrometer and and IR SpectrumLG Ch 3 p 3Which of the following represent the scissor, rocking, wagging, and twisting vibrations of a CH2 group?CH HCH HCHHHCHCHHCHCHCH HHHWhich vibrations in a molecule will we be concerned with?II. Molecular vibrationsWhy do molecules absorb infrared light?What are the two types of vibrations that molecules can undergo?What does a stretching vibration look like in an HCl molecule?What does a symmtrical and unsymmetrical vibration look like in a water molecule?Which of these is the molecule actually doing?What does an IR spectrum look like?Types of vibrationsLG Ch 3 p 4Predict which of the following bands will have the higher frequency, and explain why.C HC C1) size of atoms2) bond orderC CC CC C3) type of vibrationCHHCHHCHHCHHPredict which of the following vibrations will absorb more light, and explain why.O1) strength of dipole2) number of bondsOOFactors which affect a bandLG Ch 3 p 5What are the two main regions of the frequency axis?The spectra of two different alcohols are shown below. Which bands belong tot he functional group region, and which to the fingerprint region? If you take a spectum of an unknown compound, what can you deduce about it from the spectum?What would you need to be able to identify the compound?Regions of the IR SpectrumLG Ch 3 p 6III. Identifying functional groupsThe following bonds absorb IR light at known frequencies. They are useful for deducing the functional groups of compounds.C HC HC HO HN HO HonC OC CC CC NC OC CaromaticNH2 bendingCH2 bendingaromatic overtonesC HCOOH dimerC=C bendingC XC CC OononC ConC OFor each of the functional groups below, write down which of these bands it should have. The number of bands you should look for is given in ( ).alkane (2)alkene (5)alkyne (4)aromatic ring (5)alcohol (4)ether (3)OHOLG Ch 3 p 7carboxylic acid (6)aldehyde (4)ketone (3)OHOOHOester (4)anhydride (4)amine (4)amide (5)nitrile (3)OOOOONH2NH2ONalkyl halide (3)ClWhich bands would you expect to find in the following ranges?3400-3200 cm-13100-2700 cm-12250-2100 cm-12000-1600 cm-11300-400 cm-1LG Ch 3 p 8Using the charts on the previous pages, identify the important bands for each functional group.AlcoholOHAlkyneAlkanehexane1-heptanolcyclohexylacetyleneLG Ch 3 p 9KetoneOAnhydrideOOOAmineNH2HN3-pentanonepropanoic anhydridebutyl amine expected bands:expected bands:expected bands:N2o amine 3o amine1o amineLG Ch 3 p 10AlkeneNitrileCarboxylic acidOOHN1-octenebutanenitrilebutanoic acidLG Ch 3 p 11AmideONH2AldehydeOHAlkyl halideBrbromomethylcyclohexaneN-methylpropanamide3-methylpentanal expected bands:expected bands:expected bands:LG Ch 3 p 12EsterOOEtherAromaticsec-butyl benzeneethyl butyratedibutyl etherOIV. Interpreting an IR spectrumLG Ch 3 p 13If you think you know the identity of a compound that you have a spectrum of, what should you do?alcoholesteralkeneIf you don't know the identity of the compound you have a spectrum of, what should you do?2) look in each area for bands that stick out3) then look for bands that confirm, or narrow it downif you see an O-H, look for:if you see an N-H, look for:if you see a C C or C N, look for:if you see a C=O, look for:if there are no obvious bands, look for:1) find C-H and CH2 bending to use as reference pointsLG Ch 3 p 14How would you tell spectra of the following compounds apart?aldehyde vs. ketone?alcohol vs. carboxylic acid?nitrile vs. alkyne?ketone vs. ester?amide vs. amine?alkane vs. ether?alcohol vs. amine?What would you look for in the IR spectum of the following