Organic Chemistry Spectroscopy

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    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.

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    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).

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    Carboxylic acids:

    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.

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    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.

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    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.

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    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.

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    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.

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    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.

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Card Set:
Organic Chemistry Spectroscopy
2014-10-08 22:34:08
organic chemistry spectroscopy chapter 13 carey

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