Organic Chemistry Spectroscopy
Home > Preview
The flashcards below were created by user
on FreezingBlue Flashcards.
A broad peak at 3200–3400 /cm is characteristic of hydrogen-bonded OH groups. In dilute solution, hydrogen bonding is less, and a sharp second peak for “free” OH groups appears near 3600 /cm.
The peak at 1070 /cm lies in the range given in Table 13.4 (1025–1200 /cm) for C-O stretching and can be assigned to it.
The C-=N triple bond absorption is easily identifiable in the IR spectrum of a nitrile as a sharp peak of medium intensity at 2240–2280 /cm.
Very few other groups absorb in this region, the most notable being C-=C triple bonds (2100–2200 /cm).
Carboxylic acids have two characteristic absorptions: a broad peak for O-H stretching in the range 2500–3600 /cm and a strong peak for C=O stretching at 1700–1725 /cm.
Aldehydes and Ketones:
As in other carbonyl-containing compounds, the C=O stretching vibration gives the strongest peak in the IR spectra of aldehydes and ketones.
The C=O stretching frequencies of aldehydes are similar to those of ketones.
The C-H stretch of the CH=O group in aldehydes appears as a pair of bands in the range 2700–2900 /cm.
In addition to a strong C=O absorption(1730–1750 /cm), esters exhibit peaks for symmetric and antisymmetric C-O-C stretching at 1050–1300 /cm.
Peaks for C-O-C stretching in ethers appear in the range 1070–1150 /cm. Ethers of the type ROR' where R and R' are different have two peaks in this region.
Primary amines (RNH2) have two peaks for the NH2 group in the 3300–3500 /cm region, one for symmetric and the other for antisymmetric N-H stretching. Secondary amines (RNHR') have only one peak (3310–3350 /cm).
An NH bending peak at 650–900 /cm occurs in both RH2 and RNHR'. Primary amines also have an NH bending absorption at 1580–1650 /cm. C-N stretching peaks are found at 1020–1250 /cm.
Amides of the type RC(O)NH2 have peaks for both symmetric (3400 /cm) and antisymmetric(3500 /cm) N-H stretching.
The C=O absorption for amides appears at slightly lower frequency (1650–1700 /cm) than for ketones. Amides have a peak for NH2 bending at a slightly lower frequency (1600–1650 /cm)than C=O.
Home > Flashcards > Print Preview