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Infrared Tables (Short Summary of Common Absorption Frequencies)

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Infrared Tables (Short Summary of Common Absorption Frequencies) Beauchamp Spectroscopy Tables 1 Infrared Tables (short summary of common absorption frequencies) The values given in the tables that follow are typical values. Specific bands may fall over a range of wavenumbers, cm-1. Specific substituents may cause variations in absorption frequencies. Absorption intensities may be stronger or weaker than expected, often depending on dipole moments. Additional bands may confuse the interpretation. In very symmetrical compounds there may be fewer than the expected number of absorption bands (it is even possible that all bands of a functional group may disappear, i.e. a symmetrically substituted alkyne!). Infrared spectra are generally informative about what functional groups are present, but not always. The 1H and 13C NMR’s are often just as informative about functional groups, and sometimes even more so in this regard. Information obtained from one spectroscopic technique should be verified or expanded by consulting the other spectroscopic techniques. IR Summary - All numerical values in the tables below are given in wavenumbers, cm-1 Bonds to Carbon (stretching wave numbers) sp3 C-X single bonds sp2 C-X single bonds CN CO CO CC CC CN 1000-1350 1050-1150 1100-1350 not used not very useful alkoxy C-O not very useful 1250 acyl and phenyl C-O sp2 C-X double bonds sp C-X triple bonds CO CC CN CC CN 1640-1810 expanded table 1600-1680 1640-1690 on next page 2100-2250 2240-2260 Stronger dipoles produce more intense IR bands and weaker dipoles produce less intense IR bands (sometimes none). Bonds to Hydrogen (stretching wave numbers) CH O CCH CH CH 3000-3100 sp3 C-H 3300 2700-2760 3 2800-2860 2850-3000 2 sp C-H (see sp C-H bend aldehyde C-H 3 sp C-H patterns below) (sp C-H bend ≈ 620) (two bands) H O CN CN R OH C OH R SH H H 3100-3500 3100-3500 2550 -2620 primary NH2 secondary N-H 3200-3400 2500-3400 (very weak) (two bands) (one band) alcohol O-H acid O-H thiol S-H amides = strong, amines = weak Z:\classes\spectroscopy\all spectra tables for web.DOC Beauchamp Spectroscopy Tables 2 Carbonyl Highlights (stretching wave numbers) Aldehydes KetonesEsters Acids O O O O C C C R' C H R H R R R O R O saturated = 1725 saturated = 1715 saturated = 1735 saturated = 1715 conjugated = 1690 conjugated = 1680 conjugated = 1720 conjugated = 1690 aromatic = 1700 aromatic = 1690 aromatic = 1720 aromatic = 1690 6 atom ring = 1715 6 atom ring = 1735 5 atom ring = 1745 5 atom ring = 1775 4 atom ring = 1780 4 atom ring = 1840 3 atom ring = 1850 Amides Anhydrides Acid Chlorides nitro O O O O O C C C R N R O R R Cl R NR2 saturated = 1650 saturated = 1760, 1820 saturated = 1800 O conjugated = 1660 conjugated = 1725, 1785 conjugated = 1770 aromatic = 1725, 1785 aromatic = 1770 asymmetric = 1500-1600 aromatic = 1660 symmetric = 1300-1390 6 atom ring = 1670 6 atom ring = 1750, 1800 5 atom ring = 1700 5 atom ring = 1785, 1865 4 atom ring = 1745 Very often there is a very weak C=O overtone at approximately 2 x ν (≈3400 cm-1). 3 atom ring = 1850 Sometimes this is mistaken for an OH or NH peak., sp2 C-H bend patterns for alkenes sp2 C-H bend patterns for aromatics absorption absorption alkene substitution descriptive frequencies (cm-1) aromatic substitution descriptive frequencies (cm-1) alkene term aromatic term pattern due to sp2 CH bend pattern due to sp2 CH bend R H monosubstituted 985-1000 monosubstituted CC X 690-710 alkene 900-920 aromatic 730-770 H H R R X CC cis disubstituted 675-730 alkene (broad) ortho disubstituted 735-770 H H X aromatic R H CC trans disubstituted 960-990 alkene X H R R H 680-725 X meta disubstituted aromatic 750-810 CC geminal disubstituted 880-900 alkene 880-900 (sometimes) R H R R para disubstituted CC trisubstituted 790-840 alkene 790-840 X X aromatic R H R R Aromatic compounds have characteristic weak overtone bands that show up between 1650-2000 cm-1). Some books provide CC tetrasubstituted alkene none pictures for comparison (not here). A strong C=O peak will R R cover up most of this region. Z:\classes\spectroscopy\all spectra tables for web.DOC Beauchamp Spectroscopy Tables 3 units = cm-1 4000 3500 3000 2500 2000 1700 1500 1400 1300 1200 1100 1000 900 800 700 600 500 2 3 alkene sp C-H sp C-H sp C-H CC C=O 3 bend stretch stretch stretch sp C-H thiol S-H bend mono sp2 C-H stretch C=N cis stretch CN stretch trans aldehyde C-H acyl C-O geminal stretch phenol C-O C=C stretch tri alcohol O-H alkene stretch alkoxy C-O C=C stretch carboxylic acid O-H aromatic sp2 C-H stretch aromatic bend 1o N-H mono 2 N-H bend stretch ortho 2o N-H nitro nitro meta stretch para 3500 4000 3000 2500 2000 1700 15001400 1300 1200 1100 1000 900 800 700 600 500 expansion of alkene & aromatic sp2 C-H bend region (units = cm-1) 1000 900 800 700 600 500 mono mono cis alkene sp2 C-H trans geminal bend tri mono mono 2 ortho aromatic sp C-H bend meta meta meta para expansion of carbonyl (C=O) stretch region (units = cm-1) 1800 1750 1700 1650 1600 Saturated C=O lies at carboxylic acid C=O (also acid "OH") Conjugated C=O higher cm-1 lies at lower cm-1 C=O in samll rings ester C=O (also acyl C-O and alkoxy C-O) lies at higher cm-1 aldehyde C=O (also aldehyde C-H) ketone C=O (nothing special) amide C=O (low C=O, amide N-H) acid chloride C=O (high C=O, 1 peak) anhydride C=O anhydride C=O (high C=O, 2 peaks) Z:\classes\spectroscopy\all spectra tables for web.DOC Beauchamp Spectroscopy Tables 4 IR Flowchart to determine functional groups in a compound (all values in cm-1). IR Spectrum has C=O band (1650-1800 cm-1) does not have C=O band very strong CC CN aldehydes O alkanes 1725-1740 (saturated) 3 2850-3000 nitriles ≈ 2250 sp C-H stretch C 1660-1700 (unsaturated) sharp, stronger 3 1460 & 1380 sometimes lost than alkynes, sp C-H bend 3 CN 2860-2800 in sp CH peaks CC not useful aldehyde C-H 2760-2700 a little lower (both weak) when conjugated alkenes sp2 C-H stretch 3000-3100 ketones alkynes 650-1000 O 2150 sp2 C-H bend (see table for 1710-1720 (saturated) CC spectral patterns) 1680-1700 (unsaturated) (variable intensity) C 1715-1810 (rings: higher not present or weak when symmetrically CC 1600-1660 in small rings) substituted, a little lower when conjugated weak or not present esters - rule of 3 O sp C-H stretch 3300 aromatics 1735-1750 (saturated) sharp, strong 1715-1740 (unsaturated) sp2 C-H stretch 3050-3150 C 1735-1820 (higher in small rings) sp C-H bend 620 690-900 (see table), 2 overtone patterns acyl sp C-H bend All IR values are approximate and have a range between 1660-2000 CO 1150-1350 (acyl, strong) of possibilities depending on the molecular 1600 & 1480 alkoxy (1000-1150, alkoxy, medium) CO environment in which the functional group resides. CC can be weak Resonance often modifies a peak's position acids because of electron delocalization (C=O lower, alcohols O acyl C-O higher, etc.). IR peaks are not 100% 1700-1730 (saturated) alcohol reliable. Peaks tend to be stronger (more intense) 3600-3500 1715-1740 (unsaturated) OH C 1680-1700 (higher in small rings) when there is a large dipole associated with a vibration in the functional group and weaker in alkoxy 1000-1260 less polar bonds (to the point of disappearing in o o o acyl CO (3 > 2 > 1 ) CO 1210-1320 (acyl, strong) some completely symmetrical bonds). thiols ≈ 2550 (weak) acid 2400-3400, very broad thiol (easy to overlook) OH (overlaps C-H stretch) Alkene sp2 C-H bending patterns SH amides amines O H monosubstituted alkene (985-1000, 900-920) 3300 - 3500, two bands 1630-1680 (saturated) geminal disubstituted (960-990) for 1o amines, one band C 1745 (in 4 atom ring) N cis disubstituted (675-730) for 2o amines, weaker 1o NH trans disubstituted (880-900) H o H 3350 & 3180, two bands 2 than in amides, o trisubstituted (790-840) for 1 amides, 2 N o tetrasubstituted (none, no sp C-H) NH N-H bend, 1550-1640, one band for 2 amides, stronger in amides than amines 1o NHstronger than in amines, extra H 2o overtone sometimes at 3100 NC 1000-1350 Aromatic sp2 C-H bending patterns (uncertain) ethers NH N-H bend, 1550-1640, monosubstituted (730-770, 690-710) 1120 (alphatic) stronger in amides than amines alkoxy ortho disubstituted (735-770) CO 1040 & 1250 (aromatic) meta disubstituted (880-900,sometimes, acid chlorides nitro compounds 750-810, 680-725) O 1800 (saturated) O 1770 (unsaturated) para disubstituted (790-840) 1500-1600, asymmetric (strong) C Inductive pull of Cl increases the N 1300-1390, symmetric (medium) electron density between C and O. There are also weak overtone bands between O anhydrides 1660 and 2000, but are not shown here. You O can consult pictures of typical patterns in other carbon-halogen bonds 1760 & 1820 (saturated) reference books. If there is a strong C=O band, 1725-1785 (unsaturated) they may be partially covered up.
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