Interpreting Carbon NMR Spectra 1H and 13C NMR compared: Both spectra give us information about the number of chemically nonequivalent nuclei (nonequivalent hydrogens or nonequivalent carbons) Both spectra give us information about the environment of the nuclei (hybridization state, attached atoms, etc.) It is convenient to use FT-NMR techniques for 1H It is standard practice to use FT-NMR for 13C NMR continue….. MC 13.3 Spectroscopy, Pt III

Interpreting Carbon NMR Spectra (cont) 1H and 13C NMR compared (cont): 13C requires FT-NMR because the signal for a carbon atom is 10-4 times weaker than the signal for a hydrogen atom A signal for a 13C nucleus is only about 1% as intense as that for 1H because of the magnetic properties of the nuclei In addition, at the "natural abundance" level only 1.1% of all the C atoms in a sample are 13C (most are 12C) 13C signals are spread over a much wider range than 1H signals making it easier to identify and count individual nuclei continue….. MC 13.3 Spectroscopy, Pt III

Interpreting Carbon NMR Spectra (cont) 1H and 13C NMR compared (cont): 13C requires FT-NMR because the signal for a carbon atom is 10-4 times weaker than the signal for a hydrogen atom A signal for a 13C nucleus is only about 1% as intense as that for 1H because of the magnetic properties of the nuclei, and In addition, at the "natural abundance" level only 1.1% of all the C atoms in a sample are 13C (most are 12C) continue….. MC 13.3 Spectroscopy, Pt III

Interpreting Carbon NMR Spectra (cont) Cl CH2 CH2 CH2 CH2 CH3 1H NMR Spectrum: CH2 CH3 Cl CH2 CH2 2 4 3 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 Chemical shift (, ppm) continue…..

Interpreting Carbon NMR Spectra (cont) Cl CH2 CH2 CH2 CH2 CH3 13C NMR Spectrum: Chemical shift (, ppm) 20 40 60 80 100 120 140 160 180 200 A separate, distinct peak appears for each of the 5 carbons CDCl3 continue….. MC 13.3 Spectroscopy, Pt III

Interpreting Carbon NMR Spectra (cont) 13C Chemical Shifts: Just as in 1H NMR spectroscopy, chemical shifts in 13C NMR depend on the electron density around the carbon nucleus Decreased electron density causes the signal to move downfield (deshielding) Increased electron density causes the signal to move upfield (shielding) Because of the wide range of chemical shifts, it is rare to have two 13C peaks coincidentally overlap A group of 3 peaks at d 77 comes from the common NMR solvent deuteriochloroform and can be ignored continue….. MC 13.3 Spectroscopy, Pt III

Interpreting Carbon NMR Spectra (cont) 13C Chemical Shifts (cont): continue….. MC 13.3 Spectroscopy, Pt III

Interpreting Carbon NMR Spectra (cont) DEPT 13C NMR: DEPT (distortionless enhanced polarization transfer) spectra are created by mathematically combining several individual spectra taken under special conditions The final DEPT spectra explicitly show C, CH, CH2 , and CH3 carbons To simplify the presentation of DEPT data, the broadband decoupled spectrum is annotated with the results of the DEPT experiments using the labels C, CH, CH2 and CH3 above the appropriate peaks continue….. MC 13.3 Spectroscopy, Pt III

Interpreting Carbon NMR Spectra (cont) Cl CH2 CH CH3 OH DEPT 13C NMR: (a) The 13C spectrum and (b) a set of DEPT spectra showing the separate CH, CH2, and CH3 signals continue…..

Interpreting Infrared Spectroscopy Infrared spectroscopy gives information about the functional groups in a molecule The region of infrared that is most useful lies between 2.5-16 m (4000-625 cm-1) The infrared absorption depends on transitions between vibrational energy states Stretching Bending MC 13.3 Spectroscopy, Pt III continue…..

Interpreting Infrared Spectroscopy (cont) Stretching Vibrations of a CH2 Group: Symmetric Antisymmetric MC 13.3 Spectroscopy, Pt III continue…..

Interpreting Infrared Spectroscopy (cont) Bending Vibrations of a CH2 Group: In plane In plane MC 13.3 Spectroscopy, Pt III continue…..

Interpreting Infrared Spectroscopy (cont) Bending Vibrations of a CH2 Group (cont): Out of plane Out of plane MC 13.3 Spectroscopy, Pt III continue…..

Interpreting Infrared Spectroscopy (cont) CH3CH2CH2CH2CH2CH3 Infrared Spectrum of Hexane: bending C—H stretching bending bending CH3CH2CH2CH2CH2CH3 2000 3500 3000 2500 1000 1500 500 Wave number, cm-1 continue…..

Interpreting Infrared Spectroscopy (cont) H2C=CHCH2CH2CH2CH3 Infrared Spectrum of 1-Hexene: C=C H C C=C H H2C=C H2C=CHCH2CH2CH2CH3 2000 3500 3000 2500 1000 1500 500 Wave number, cm-1 continue…..

Interpreting Infrared Spectroscopy (cont) Infrared Absorption Frequencies: Structural unit Frequency, cm-1 Stretching Vibrations (single bonds): sp C — H 3310-3320 sp2 C — H 3000-3100 sp3 C — H 2850-2950 sp2 C — O 1200 sp3 C — O 1025-1200 continue….. MC 13.3 Spectroscopy, Pt III

Interpreting Infrared Spectroscopy (cont) Infrared Absorption Frequencies (cont): Structural unit Frequency, cm-1 Stretching Vibrations (multiple bonds): C 1620-1680 — C C — 2100-2200 — C N 2240-2280 continue….. MC 13.3 Spectroscopy, Pt III

Interpreting Infrared Spectroscopy (cont) Infrared Absorption Frequencies (cont): Structural unit Frequency, cm-1 Stretching Vibrations (carbonyl groups): Aldehydes and ketones 1710-1750 Carboxylic acids 1700-1725 Acid anhydrides 1800-1850 and 1740-1790 Esters 1730-1750 Amides 1680-1700 C O continue….. MC 13.3 Spectroscopy, Pt III

Interpreting Infrared Spectroscopy (cont) Infrared Absorption Frequencies (cont): Structural unit Frequency, cm-1 Bending Vibrations of Alkenes: CH2 RCH 910-990 CH2 R2C 890 CHR' cis-RCH 665-730 CHR' trans-RCH 960-980 CHR' R2C 790-840 continue…..

Interpreting Infrared Spectroscopy (cont) Infrared Absorption Frequencies (cont): Structural Unit Frequency, cm-1 Bending Vibrations of Derivatives of Benzene: Monosubstituted 730-770 and 690-710 ortho-Disubstituted 735-770 meta-Disubstituted 750-810 and 680-730 para-disubstituted 790-840 continue….. MC 13.3 Spectroscopy, Pt III

Interpreting Infrared Spectroscopy (cont) C6H5C(CH3)3 Infrared Spectrum of tert-butylbenzene: Ar H Aromatic Double Bond H C Monsubstituted Benzene C6H5C(CH3)3 2000 3500 3000 2500 1000 1500 500 Wave number, cm-1 continue…..

Interpreting Infrared Spectroscopy (cont) Infrared Absorption Frequencies (cont): Structural Unit Frequency, cm-1 Stretching Vibrations (single bonds): O — H (alcohols) 3200-3600 O — H (carboxylic acids) 3000-3100 N — H 3350-3500 continue….. MC 13.3 Spectroscopy, Pt III

Interpreting Infrared Spectroscopy (cont) Infrared Spectrum of 2-Hexanol: H C O H OH CH3CH2CH2CH2CHCH3 2000 3500 3000 2500 1000 1500 500 Wave number, cm-1 continue….. MC 13.3 Spectroscopy, Pt III

Interpreting Infrared Spectroscopy (cont) Infrared Spectrum of 2-Hexanone: O CH3CH2CH2CH2CCH3 H C C = O 2000 3500 3000 2500 1000 1500 500 Wave number, cm-1 continue….. MC 13.3 Spectroscopy, Pt III