Carbonyl - compounds - IR, Lecture notes of Organic Chemistry

Download Carbonyl - compounds - IR and more Lecture notes Organic Chemistry in PDF only on Docsity! IR — Spectroscopy Part I sew ON se 8 OM Carbonyl - compounds For simple aldehydes and ketones, the stretching vibration of the carbonyl group has a strong infrared absorption between 1710 and 1740 cm-1. Alkyl substituents are Electron Donating Groups – inductive effect lower the bond strength of C=O ketone carbonyls have slightly lower stretching frequencies, 1715 ± 7 cm-1, compared with aldehydes, 1730 ± 7 cm-1. 2 Ketones and aldehydes – conjugated systems Conjugation of C=O bond with a double bond or phenyl ring lowers the stretching frequency. 5 Ketones and aldehydes — conjugated systems 100 3407 L oO # Beso 5 = & = & 2864 2942 a7a6 ° Tr T T T T T 4000 3000 2000 1800 1000 500 Waevenurniber cnn * op 1685 cm? o T T T ana 3000 200 1 1 isha ferry 6 5m WAIVENUTIBER 11 Ketones and aldehydes – influence of EDG and EWG 7 Ketones– ring size Incorporation of the carbonyl group into a small ring, increase the stretching frequency. 10 O° By 1807 cm! O° O° AK 1761 cm 1832 cm’! Oo AY 1768 cm! Carbonyl compounds 1D ° nw 1760 cm monomer "i A peu 1749 em 1719 cm! 1710 cm! dimer Ay 4 1688 cm! Ae 1662 cm oO As 1413 cm? 1563 cm! ell Acid chlorides –aliphatic - butyryl chloride Additional band in C=O region is a result of Fermi resonance of C-Cl and C=O 12 Carboxylic acid – hydrogen bonds Spectrum of carboxylic acid in gas phase – only monomeric molecules 15 Carboxylic acid – hydrogen bonds Spectrum of carboxylic acid in solution– dimeric and monomeric 16 Carboxylic acid – hydrogen bonds Spectrum of liquid carboxylic acid (pure substance) – only dimer is observed 17 Secondary Amides ν NH 3326 cm-1 ν C=O 1638 cm-1 δ NH (in plane) 1554cm-1 ω NH (out of plane) 711cm-1 645 One stretching band ν C-N 1450 cm-1 ω CH aromatic (out of plane) 711cm-1 645 20 TertiaryAmides None N-H stretching band Overtone C=O 3471 cm-1 ν C=O 1640 cm-1 ν C-N 1428 cm-1 21 Lactams • 1° & 2°-amides, 1510 to 1700 cm-1 (2 bands) • 3°-amides, 1650± 15 (one band); • 6-membered lactams, 1670 ± 10 (one band) • 5-membered lactams, 1700 ± 15 ; • 4-membered lactams, 1745 ± 15. ν C=O 1640 cm-1 non-cyclic amides cyclic amides ν C=O 1671 cm-1 ν C=O 1666cm-1 ν C=O 1700cm-1 ν C=O 1745 cm-1 22 Alcoholic C-O Stretch Alcohol Type Absorption Range cm-1 1 Saturated tertiary Secondary (highly symmetrical) 1205-1124 3 Secondary saturated, α-unsaturated or cyclic tertiary 1124-1087 4 Secondary α-unsaturated, Secondary alicyclic five or six- membered ring, Saturated primary 1085-1050 5 Tertiary, highly α-unsaturated Secondary di-α-unsaturated Secondary α-unsaturated Secondary alicyclic seven or eight membered ring Primary α-unsaturated <1050 25 Alcoholic C-O Stretch ν C-O 1205 cm-1 ν C-O 1130 cm-1 1160 cm-1 26 Alkyls - Tert-butyl ver isopropyl cm-1 H) 1480 cm-1 as CH 3 and s CH 2 1390 and 1370 cm-1 s CH3 dublet and cm-1 C-O) 600 -650 cm-1 H) out of plane 27 Aromatic Ring Substitution- overtones of γ – out of plane vibration 2000 cm-1 1667 cm-1 30 Mono substituted 2000 cm-1 1667cm-1 910-890 770-730 710-680 m* s s 31 Transmittance %T Ortho substituted 100 504 3050 ene pl C-H stretch 3018 CHs 1495 1467 ortho-xylene 742 CH3 4 T T T T T T 4000 3000 2000 1500 1900 500 wavenumber cm” 2000 cm? 1667 cm? Cc @32 EWG substituted aromatic ring 2000 cm-1 1667 cm-1 682 703 794 852 νas NO2 νs NO2 910-890 770-730 710-680 m* s s 935 mono- 860-800 s para- ? 35 Alkenes substitution Structure (γ) bending out of plane [cm-1] (ν) stretching =C-H [cm-1] (ν) stretching C=C [cm-1] overtones 1 1005-985 s 920-900 s 3095-3075 m 3040-3010 m 1660-1635 m 1860-1800 m 2 900-880 s 3095-3075 m 1660-1640 m 1800-1750 m 3 990-960 s 3040-3010 m 1690-1665 w ------------------- 4 730-665 m 3040-3010 m 1690-1665 w ------------------- 5 850-790 m 3040-3010 m 1690-1665 w-m (sometimes absent) ------------------- 6 -------------- ---------------- 1690-1650 w (sometimes absent) ------------------- 36 Alkenes substitution - terminal CH2 3080 cm-1 CH) C=CH 2 1826 cm-1 CH) C=CH 2 overtone 1643 cm-1 C=C) 1417 cm-1 s CH) C=CH 2 scissoring 993 i 912 cm-1 CH) C=CH 2 bendinging out of-plane 1 1005-985 s 920-900 s 3095-3075 m 3040-3010 m 1660-1635 m 1860-1800 m 37