infrared spec to s copy
DESCRIPTION
spectroscopyTRANSCRIPT
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SpectroscopyInfrared Spectra
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Infrared spectra in this presentation are taken by permission from the SDBS web site:
SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/
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Spectroscopyseeing the unseeableUsing electromagnetic radiation as a probe to obtain information about atoms and molecules that are too small to see.Electromagnetic radiation is propagated at the speed of light through a vacuum as an oscillating wave.
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electromagnetic relationships: = c 1/E = hE E = hc/E 1/
= wave length = frequencyc = speed of lightE = kinetic energyh = Plancks constant
c
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Two oscillators will strongly interact when their energies are equal.E1 = E21 = 21 = 2If the energies are different, they will not strongly interact!We can use electromagnetic radiation to probe atoms and molecules to find what energies they contain.
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some electromagnetic radiation rangesApprox. freq. rangeApprox. wavelengths Hz (cycle/sec) meters
Radio waves 104 - 1012 3x104 - 3x10-4Infrared (heat) 1011 - 3.8x1014 3x10-3 - 8x10-7Visible light 3.8x1014 - 7.5x1014 8x10-7 - 4x10-7Ultraviolet 7.5x1014 - 3x1017 4x10-7 - 10-9X rays 3x1017 - 3x1019 10-9 - 10-11Gamma rays > 3x1019 < 10-11
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Infrared radiation = 2.5 to 17 m = 4000 to 600 cm-1These frequencies match the frequencies of covalent bond stretching and bending vibrations. Infrared spectroscopy can be used to find out about covalent bonds in molecules.
IR is used to tell:1. what type of bonds are present2. some structural information
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IR source sample prism detector graph of % transmission vs. frequency=> IR spectrum40003000200015001000 500v (cm-1)100
%T
0
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toluene
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Some characteristic infrared absorption frequenciesBONDCOMPOUND TYPEFREQUENCY RANGE, cm-1C-Halkanes2850-2960 and 1350-1470alkenes3020-3080 (m) andRCH=CH2910-920 and 990-1000R2C=CH2880-900cis-RCH=CHR675-730 (v)trans-RCH=CHR965-975aromatic rings3000-3100 (m) andmonosubst.690-710 and 730-770ortho-disubst.735-770meta-disubst. 690-710 and 750-810 (m)para-disubst.810-840 (m)alkynes3300O-Halcohols or phenols3200-3640 (b)C=Calkenes1640-1680 (v)aromatic rings1500 and 1600 (v)CCalkynes2100-2260 (v)C-Oprimary alcohols1050 (b)secondary alcohols1100 (b)tertiary alcohols1150 (b)phenols1230 (b)alkyl ethers1060-1150aryl ethers1200-1275(b) and 1020-1075 (m) all abs. strong unless marked: m, moderate; v, variable; b, broad
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IR spectra of ALKANESCH bond saturated(sp3) 2850-2960 cm-1 + 1350-1470 cm-1
-CH2- + 1430-1470-CH3 + and 1375 -CH(CH3)2 + and 1370, 1385-C(CH3)3 + and 1370(s), 1395 (m)
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n-pentaneCH3CH2CH2CH2CH3
3000 cm-11470 &1375 cm-12850-2960 cm-1satd C-H
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CH3CH2CH2CH2CH2CH3n-hexane
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2-methylbutane (isopentane)
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2,3-dimethylbutane
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cyclohexaneno 1375 cm-1no CH3
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IR of ALKENES=CH bond, unsaturated vinyl(sp2)3020-3080 cm-1 + 675-1000RCH=CH2 +910-920 & 990-1000R2C=CH2 +880-900cis-RCH=CHR +675-730 (v)trans-RCH=CHR +965-975
C=C bond 1640-1680 cm-1 (v)
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1-decene910-920 & 990-1000 RCH=CH2C=C 1640-1680unsatdC-H
3020-3080 cm-1
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4-methyl-1-pentene910-920 & 990-1000 RCH=CH2
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2-methyl-1-butene880-900R2C=CH2
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2,3-dimethyl-1-butene880-900R2C=CH2
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IR spectra BENZENEs=CH bond, unsaturated aryl(sp2) 3000-3100 cm-1 + 690-840mono-substituted +690-710, 730-770ortho-disubstituted + 735-770meta-disubstituted + 690-710, 750-810(m)para-disubstituted + 810-840(m)
C=C bond1500, 1600 cm-1
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ethylbenzene690-710, 730-770 mono-1500 & 1600Benzene ring3000-3100 cm-1Unsatd C-H
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o-xylene735-770ortho
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p-xylene810-840(m)para
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m-xylenemeta 690-710, 750-810(m)
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styreneno satd C-H910-920 & 990-1000RCH=CH2mono1640C=C
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2-phenylpropenemono880-900R2C=CH2Satd C-H
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p-methylstyrenepara
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IR spectra ALCOHOLS & ETHERS
CO bond1050-1275 (b) cm-11o ROH10502o ROH11003o ROH1150ethers1060-1150
OH bond3200-3640 (b)
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1-butanolCH3CH2CH2CH2-OHC-O 1o3200-3640 (b) O-H
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2-butanolC-O 2oO-H
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tert-butyl alcohol C-O 3oO-H
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methyl n-propyl etherno O--HC-O ether
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2-butanone C=O ~1700 (s)
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C9H12C-H unsatd & satd1500 & 1600benzenemonoC9H12 C6H5 = -C3H7isopropylbenzenen-propylbenzene?
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n-propylbenzene
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isopropyl split 1370 + 1385isopropylbenzene
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C8H6C-H unsatd1500, 1600benzenemonoC8H6 C6H5 = C2Hphenylacetylene3300C-H
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C4H81640-1680C=C880-900R2C=CH2isobutylene CH3 CH3C=CH2Unstd
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Which compound is this?2-pentanone1-pentanol1-bromopentane2-methylpentane1-pentanol
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What is the compound?1-bromopentane1-pentanol2-pentanone2-methylpentane2-pentanone
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In a matching problem, do not try to fully analyze each spectrum. Look for differences in the possible compounds that will show up in an infrared spectrum.
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