IR Spectroscopy Lecture 5 PDF

IR Part 1/Lecture 5  Aromatic ring C-H stretch occurs between 3050 an 3010 cm-1 C-H out of plane bending occurs at 900-690 cm-1 Note: useful for determining type of ring substitution (monosubst.oop ,orthosubst.oop, metasubst.oop, parasubst.oop) C=C stretching often occurs in...

IR Part 1/Lecture 5  Aromatic ring C-H stretch occurs between 3050 an 3010 cm-1 C-H out of plane bending occurs at 900-690 cm-1 Note: useful for determining type of ring substitution (monosubst.oop ,orthosubst.oop, metasubst.oop, parasubst.oop) C=C stretching often occurs in pairs at 1600 cm-1 and 1475 cm-1 Aromatic ring Aromatic ring Aromatic ring  Oxygen-Containing Compounds Oxygen-Containing Compounds 1. Alcohols and Phenols Alcohols and phenols produce characteristic infrared bands due to O–H stretching and C–O stretching, which are both sensitive to hydrogen bonding. For alcohols, the broad O–H stretching band is centred at 3600 cm−1, while for phenols this band appears 50–100 cm−1 lower than the alcohol wavenumber. ✓The sheer size and broad shape of the band dominate the IR spectrum and make it hard to miss. C–O stretching in alcohols and phenols produces a strong band in the 1300– 1000 cm−1 region. IR SPECTRUM OF AN ALCOHOL  IR SPECTRUM OF AN ALCOHOL 1.Hexanol  Para-cresol  Carbonyl compounds Carbonyl compounds are those that contain the C=O functional group. Is present in aldehydes,ketones,esters,amide,acidchloride &anhydrides. This group absorbs strongly in the range of in the range from1850 to 1650 cm-1.  Carbonyl compounds a. Aldehydes and ketones C=O show a strong, prominent, stake-shaped band around 1710 - 1720 cm-1 (right in the middle of the spectrum). This band is due to the highly polar C=O bond. Because of its position, shape, and size, it is hard to miss. Because aldehydes also contain a C-H bond to the sp2 carbon of the C=O bond, they also show a pair of medium strength bands positioned about 2700 and 2800 cm-1. These bands are missing in the spectrum of a ketone because the sp2 carbon of the ketone lacks the C-H bond.