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JOURNAL OF THE OPTICAL SOCIETY OF AMERICASpectra-Structure Correlations in the Infra-Red Region

N. B. COLTHUPStamford Research Laboratories,American Cyanamid Company, Stamford, Connecticut(Received March 17, 1950)

This paper presents a chart giving probable positions of characteristic infra-red absorption bands forcertain molecular groupings. Both original and published data were used in its preparation. The reliabilityof the various correlations is discussed in the text.

A CHART is presented summarizing our knowledgeconcerning the probable positions of the charac-teristic infra-red absorption bands of specific groupsfrom 4000to 400 wave numbers. Especial attention hasbeen given to the region below 1400 wave numberswhere specific group vibrations are complicated by theirinteraction with the rest of the molecule. This difficultyis particularly noticeable for assignments in the singlebond region for such groups as ethyl, propyl, aldehyde,ketone, etc., where the bands are relatively weak andquite sensitive to the manner in which these groupsare attached to the rest of the molecule.Some of the data were taken from the literature andmost of these have been rechecked and extended in thecourse of routine work. The rest of the correlations aremade from unpublished work done in these Labora-tories.As some of the correlations are tentative and muchoverlapping of band positions occurs, this chart shouldbe used with discretion mainly as an aid in extrapolatingfrom known compounds to unknown samples.The indicated regions on the chart are the regionswithin which the band is normally expected to fall. Theabbreviations s, m, and w under the region markersindicate that the band is generally strong, medium,or weak.The alkane groups are characterized by the wellknown carbon-hydrogen stretching (3000-2800 cm-) 1 2and carbon-hydrogen bending (1475-1300cm-')' bands.When the methyl group is attached to a nitrogen atomthe 2900 cm-l bands generally shift to higher waveand when it is on an oxygen atom the bandslower. When the methyl is adjacent to a carbonylin acetates and methyl ketones, all the bands areshifted somewhat and the 1370cm-l band is intensified.similar intensification occurs for the 1420cm-l banda methylene is adjacent to a carbonyl or nitrileThe C-H bending band at 1340cm-' is weak inbut is intensified when this group isto an oxygen or nitrogen atom.A branched methyl grouping such as isopropyl andgenerally results in a splitting of the1370 cm-1 band and gives rise to the branched single

I R. B. Barnes, R. C. Gore, U. Liddel, and V. Z. Williams, Infra-(Reinhold Publishing Company, New York,2 E. L. Saier and N. D. Coggeshall, Anal. Chem. 20, 812 (1948).

bond vibrations around 1200 cm-.3 The correlations ofthe single bond stretching bands of ethyl and n-propyl4between 1100 and 800 cm-' are less reliable as thebands are sometimes weak. In addition these particularcorrelations apply only when the groups are attachedto a carbon, nitrogen, or oxygen atom. Attachment toheavier atoms such as sulfur shifts these bands tolower wave numbers.When four or more methylene groups are adjacent ina chain, they give rise to a fairly reliable medium strongrocking band at 730 cm7'.' When there are less thanfour, this band shifts to a higher wave number.The alkene and alkyne groups have been well coveredin the literature- 0 The out-of-plane hydrogen bendingvibrations give rise to strong bands from 1000 to 600cm-' and the in-plane hydrogen bending vibrations from1450 to 1250 cm-'. These are quite sensitive to thetype of alkene present. The medium strong double andtriple bond bands are lowered by conjugation andweakened if they are centrally located in the molecule.

The hydrogen stretching bands are higher than for thealkane groups, centering around 3000 cm-l for alkenesand 3250 cm-l for alkynes.Aromatic groups 11 re characterized below 1400cm-lby a series of sharp bands between 1200and 1000cm-land by the strong out-of-plane hydrogen bending bandsbetween 900 and 675 cm-l. These latter are the mostuseful in substitution studies. Five adjacent hydrogenatoms on the ring, as in monosubstituted benzene,generally give rise to bands at 700 cm-l and 740 cm-l,four adjacent hydrogen atoms as in ortho disubstitutiongive rise to a band at 750 cm-l, three as in meta andvicinal trisubstitution at.780 cm-', two as in para andunsymmetrical trisubstitution at 820 cm-', and one

3G. B. B. M. Sutherland and D. M. Simpson, J. Chem. Phys.15, 153 (1947).4K. W. F. Kohlrausch, Ramanspektrtn (Akademische Verlags-gesellschaft Becker and Erler, Leipzig, 1943).5N. Sheppard and G. B. B. M. Sutherland, Nature 159, 739(1947).61 . W. Thompson and P. Torkington, Trans. Faraday Soc. 61,246 (1945).7R. C. Gore and J. L. Johnson, Phys. Rev. 68, 283A (1945).8 J. E. Kilpatrick and K. S. Pitzer, J. Research Nat. Bur.Stand. 38, 191 (1947).9 . H. Wotiz and F. A. Miller, J. Am. Chem. Soc. 71, 3441(1949).10F. Halverson,R. F. Stamm and J. J. Whalen,J. Chem.Phys.16, 808 (1948).1"G. Herzberg, Infrared and Raman Spectra (D. Van NostrandCompany, New York, 1945).

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VOLUME 40, NUMBER 6 JUNE. 1950

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SPECTRA-STRUCTURE CORRELATIONS 39900

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N. B. COLTHUPisolated hydrogen atom on the ring as in meta, un-symmetrical and symmetrical trisubstitution at 860cm-'. This empirical method of classification can beextended to fit non-benzene aromatic molecules (withslightly greater deviations) such as a-naphthalenes(4 adjacent and 3 adjacent hydrogen atoms), -naph-thalenes (4 adjacent, 2 adjacent, and on 1 isolated),substituted anthracenes, substituted pyridines, tetrasubstituted benzenes and steroids.The well-known 1500 and 1600 cml bands of sub-stituted benzenes are probably caused by in-planeskeletal vibrations." The 1620 cml band shown bypara disubstitution is generally variable in intensity butis strongest when one of the substituents is ortho-paradirecting and the other meta directing.The position of the strong C-O band as in ethers,alcohols, and esters is dependent on the manner of thesubstitution of the hydrogens on the carbon atom.'2 -'4Generally, the greater the degree of substitution, thehigher will be the wave number of the band. The OHbending in primary alcohols'4 interacts with the ad-jacent methylene vibrations, giving rise to severalweak bands from 1450 to 1300 cm-'. A single strongerband appears here in tertiary alcohols and phenols.The C-O band in alcohols is sensitive to hydrogenbonding, just as is the well-known OH stretching band.Both the OH bending and the C-O stretching bandsshift to lower wave numbers when unbending occurs asit does on dilution or vaporization.The carboxylic acid carbonyl and the C-O (1300-1200 cm-l) bands are replaced by a symmetric andasymmetric vibration of the CO2 - group near 1420 and1600 cm-l when the carboxyl is ionized as in metal oramine salts or zwitterionization. In addition to the in-plane COH bending, there exists, in the acid dimeronly, an out-of-plane OH-O bending vibration which

12J. Lecompte, Trait6 de Chimie Organique, Tome II (Mas-son et Cio, 1~diteurs, Paris, 1936).13V. Z. Williams, R. Hofstadter and R. C. Herman, J. Chem.Phys. 7, 802 (1939).11A. Borden and E. F. Barker, J. Chem. Phys. 6, 553 (1938).

gives rise to a broad, medium band at 920 cm-l. Thisband has been investigated by monomer-dimer studiesof normal and deuterated acetic and formic acids.'5This type of band also appears near here in acetyl-acetone which is partially enolized giving a similarOH