1、Organic ChemistryInfrared Spectroscopy Electromagnetic Radiation light and other forms of radiant energy the distance between consecutive peaks on a wave the number of full cycles of a wave that pass a given point in a second the unit in which radiation frequency is reported;s-1(read“per second”)Ele
2、ctromagnetic RadiationuCommon units used to express wavelength A A n ng gs st tr ro om m ()1 1 =1 10 0-1 10 0 m mR R e el la at ti io on nt to o M M e et te er rU U n ni it t1 1 m m m m =1 10 0-3 3 m m1 1 n nm m =1 10 0-9 9 m m1 1 Molecular Spectroscopy the study of which frequencies of electromagne
3、tic radiation are absorbed or emitted by a particular substance and the correlation of these frequencies with details of molecular structure we study three types of molecular spectroscopyVibrational energy levelsNuclear spin statesElectronic energy levelsInfraredRadio fequencyUltraviolet-visibleAbso
4、rption ofElectromagneticRadiation Results in Transition BetweenRegion of theElectromagneticSpectrumN N u uc cl le ea ar r m m a ag gn ne et ti ic cr re es so on na an nc ce eI In nf fr ra ar re ed dU U l lt tr ra av vi io ol le et t-v vi is si ib bl le eT Ty yp pe e o of f S Sp pe ec ct tr ro os sc
5、co op py yInfrared SpectroscopyuThe vibrational IR extends from 2.5 x 10-6 m(2.5 m)to 2.5 x 10-5 m(25 m)the frequency of IR radiation is commonly expressed in wavenumbers the number of waves per centimeter,with units cm-1(read reciprocal centimeters)expressed in wavenumbers,the vibrational IR extend
6、s from 4000 cm-1 to 400 cm-1(=400 cm=400 cm-1-1=4000 cm=4000 cm-1-11010-2-2 mcm mcm-1-12.5 x 102.5 x 10-6-6 m m1010-2-2 mcm mcm-1-12.5 x 102.5 x 10-5-5 m mInfrared SpectroscopyuIR spectrum of 3-methyl-2-butanoneMolecular Vibrations atoms joined by covalent bonds undergo continual vibrations relative
7、 to each other the energies associated with these vibrations are quantized;within a molecule,only specific vibrational energy levels are allowed the energies associated with transitions between vibrational energy levels correspond to frequencies in the infrared region,4000 to 400 cm-1Molecular Vibra
8、tionsuFor a molecule to absorb IR radiation the bond undergoing vibration must be polar and its vibration must cause a periodic change in the bond dipole momentuCovalent bonds which do not meet these criteria are said to be IR inactive the C-C double and triple bonds of symmetrically substituted alk
9、enes and alkynes,for example,are IR inactive because they are not polar bondsH3CC CCH3H3CCH3H3C-C C-CH32,3-Dimethyl-2-butene2,3-Dimethyl-2-butene2-Butyne2-ButyneMolecular VibrationsuFor a nonlinear molecule containing atoms,there are allowed fundamental vibrationsuFor even a relatively small molecul
10、e,a large number of vibrational energy levels exist and patterns of IR absorption can be very complexuThe simplest vibrational motions are bending and stretchingMolecular vibrationsuFundamental stretching and bending vibrations for a methylene groupMolecular VibrationsuConsider two covalently bonded
11、 atoms as two vibrating masses connected by a spring the total energy is proportional to the frequency of vibration the frequency of a stretching vibration is given by an equation derived from Hookes law for a vibrating springK=a force constant,which is a measure of the bonds strength;force constant
12、s for single,double,and triple bonds are approximately 5,10,and 15 x 105 dynes/cm =reduced mass of the two atoms,(m1m2)/(m1+m2),where m is the mass of the atoms in gramsK K Molecular VibrationsuFrom this equation,we see that the of a stretching vibration is proportional to the strength of the vibrat
13、ing bond is inversely proportional the masses of the atoms connected by the bonduThe of absorption depends primarily on the polarity of the vibrating bondK K Correlation Tables Characteristic IR absorptions for the types of bonds and functional groups we deal with most oftenC C-H HN N-H HO O-H HC C=
14、O OC C=C CC C-O O1 10 00 00 0-1 12 25 50 0s st tr ro on ng gw w e ea ak k t to o m m e ed di iu um m1 16 60 00 0-1 16 68 80 01 16 63 30 0-1 18 82 20 0s st tr ro on ng g2 27 70 00 0-3 33 30 00 0w w e ea ak k t to o m m e ed di iu um mw w e ea ak k t to o s st tr ro on ng g3 32 20 00 0-3 36 65 50 0m m
15、 e ed di iu um m3 31 10 00 0-3 35 55 50 0I In nt te en ns si it ty yS St tr re et tc ch hi in ng gF Fr re eq qu ue en nc cy y (c cm m-1 1)B Bo on nd dHydrocarbons-Table 12.5C C-H HC CH H3 3C C=C CC C-H HC C-H HC CC CC C-C CC C-H HC C=C CC C-H HI In nt te en ns si i t ty y2 28 85 50 0 -3 30 00 00 0M
16、M e ed di iu um mS St tr re et tc ch hi in ng g3 33 30 00 0M M e ed di iu um m t to o s st tr ro on ng gS St tr re et tc ch hi in ng g2 21 10 00 0-2 22 25 50 0W W e ea ak kW W e ea ak k t to o m m e ed di iu um m1 16 60 00 0 -1 16 68 80 0S St tr re et tc ch hi in ng gW W e ea ak k t to o m m e ed di
17、 iu um m3 30 00 00 0 -3 31 10 00 0S St tr re et tc ch hi in ng gA A l lk ky yn ne eA A l lk ke en ne eA A l lk ka an ne eV V i ib br ra at ti io on nS St tr re et tc ch hi in ng gH H y yd dr ro o-c ca ar rb bo on nF Fr re eq qu ue en nc cy y(c cm m-1 1)B Be en nd di in ng g1 14 45 50 0-1 14 47 75 5M
18、 M e ed di iu um mB Be en nd di in ng g1 13 37 75 5 a an nd d 1 14 45 50 0W W e ea ak k t to o m m e ed di iu um m(N N o ot t u us se ef fu ul l f fo or r i in nt te er rp pr re et ta at ti io on n -t t o oo o m m a an ny y b ba an nd ds sA A r re en ne eS St tr re et tc ch hi in ng g3 30 03 30 0W W
19、 e ea ak k t to o m m e ed di iu um mM M e ed di iu um m1 14 45 50 0-1 16 60 00 0S St tr re et tc ch hi in ng gB Be en nd di in ng g6 69 90 0-9 90 00 0S St tr ro on ng gAlkanesuIR spectrum of decane(Fig 12.4)AlkenesuIR spectrum of cyclohexene(Fig 12.5)AlkynesuIR spectrum of 1-octyne(Fig 12.6)Aromati
20、csuIR spectrum of toluene(Fig 12.7)Alcohols IR spectrum of 1-hexanol(Fig 12.8)O O-H H (f fr re ee e)O O-H H (H H b bo on nd de ed d)C C-O OB Bo on nd dI In nt te en ns si it ty yF Fr re eq qu ue en nc cy y,c cm m-1 1M M e ed di iu um m1 10 00 00 0 -1 12 25 50 0M M e ed di iu um m,b br ro oa ad d3 32
21、 20 00 0 -3 35 50 00 03 36 60 00 0-3 36 65 50 0W W e ea ak kEthersuIR spectrum of dibutyl ether(Fig 12.9)EthersuIR spectrum of anisole(Fig 12.10)AminesuIR spectrum of 1-butanamine(Fig 12.11)IR of Molecules with C=O GroupsC C=O OC C=O OC C-H HO OH HR RC CO O H HO OR RC CH HO OR RC CR R O OC C=O OS St
22、 tr ro on ng g1 17 70 00 0-1 17 72 25 5S St tr re et tc ch hi in ng gC C a ar rb bo ox xy yl li ic c a ac ci id ds sA A l ld de eh hy yd de es sV V i ib br ra at ti io on nC Ca ar rb bo on ny yl l G G r ro ou up pF Fr re eq qu ue en nc cy y(c cm m-1 1)I In nt te en ns si it ty yS St tr re et tc ch h
23、i in ng g1 16 63 30 0-1 18 82 20 0S St tr ro on ng gS St tr re et tc ch hi in ng g2 27 72 20 0W W e ea ak kS St tr re et tc ch hi in ng g2 25 50 00 0-3 33 30 00 0S St tr ro on ng g (b br ro oa ad d)K K e et to on ne es sS St tr re et tc ch hi in ng g1 16 63 30 0-1 18 82 20 0S St tr ro on ng gIR of M
24、olecules with C=O GroupsC C=O Os sp p3 3 C CO Os sp p2 2 C CO OC C=O OC C=O ON NH HC C S St tr re et tc ch hi in ng g9 90 00 0-1 13 30 00 0S St tr ro on ng gS St tr ro on ng g1 17 73 35 5-1 18 80 00 0S St tr re et tc ch hi in ng gC Ca ar rb bo ox xy yl li i c c e es st te er rs sS St tr re et tc ch
25、hi in ng g1 10 00 00 0-1 11 10 00 0S St tr ro on ng gS St tr re et tc ch hi in ng g1 12 20 00 0-1 12 25 50 0S St tr ro on ng gA A c ci id d a an nh hy yd dr ri id de es sS St tr re et tc ch hi in ng g1 17 74 40 0-1 17 76 60 0 a an nd d1 18 80 00 0-1 18 85 50 0S St tr ro on ng gS St tr ro on ng g1 16
26、 63 30 0-1 16 68 80 0S St tr re et tc ch hi in ng gA A m m i id de es sS St tr re et tc ch hi in ng g3 32 20 00 0,3 34 40 00 0M M e ed di iu um m(1 1 a am m i id de es s h ha av ve e t tw w o o N N-H H s st tr re et tc ch he es s)(2 2 a am m i id de es s h ha av ve e o on ne e N N-H H s st tr re et
27、tc ch h)N N i it tr ri il le es sS St tr re et tc ch hi in ng g2 22 20 00 0-2 22 25 50 0M M e ed di iu um mAldehydes and KetonesuIR spectrum of menthone(Fig 12.12)Carbonyl groupsuThe position of C=O stretching vibration is sensitive to its molecular environment as ring size decreases and angle strai
28、n increases,absorption shifts to a higher frequency conjugation shifts the C=O absorption to lower frequency1850 cm1850 cm-1-11780 cm1780 cm-1-11745 cm1745 cm-1-11715 cm1715 cm-1-1OOOO1690 cm1690 cm-1-11700 cm1700 cm-1-11717 cm1717 cm-1-1OOHOCarboxylic acidsuIR spectrum of pentanoic acid(Fig 12.13)EstersuIR of ethyl butanoate(Fig 12.14)
