Group frequencies aldehydes

A second alkaloid without the oxazolidine ring, but with the carbino-lamine system is cycloneosamandaridine (XXVII). The IR-spectrum evidences a five-membered lactone ring (band at 1780 cm i) as well as the carbinolamine group (bands at 1050/1180 cm i). The IR-spectrum of the X-acetyl compound no longer shows these hands at 1050-1180 cm i, hut an additional carbonyl frequency at 1735 cm i for an aldehyde group. The mass spectrum confirms the molecular formula as well as structure XXVII(id). 

The carbonyl stretching frequency of aldehydes and ketones is found at 1730-1665 cm For example, the acyclic form of some aldoses and ketoses (in a lyophili-zate of the equilibrium mixture of mutarotation) produces a very weak band (Tipson and Isbell, 1962) at 1718 cm . Kuhn (1950) attributed the band at 1613 cm exhibited by periodate-oxidized methyl a-D-glucopyranoside to aldehydic carbonyl. Periodate-oxidized cellulose has only a very weak band (Rowen et ai, 1951), and exists mainly as the hemialdal —CH(OH)—O—CH(OH)— (Spedding, 1960), formed by hydration of two aldehyde groups per oxidized residue. 

Infared Analysis. The molecule is 4-chlorobenzaldehyde.The infrared spectrum of this aromatic aldehyde (Fig. 6.18, page 182) is rich and interesting.The aromatic aldehyde macro group frequency train (see Strategies for Interpreting Infrared Spectra) consists of peaks near 3090, 3070, 2830 and 2750, 1706, 1602, 1589, and 1396 cm ... 

The acidic product generated in the reaction is assumed to be 4-chlorobenzoic acid. This material also is a para-substituted aromatic compound thus, the spectrum of this compound (Fig. 6.17) possesses a macro frequency train (a), similar to those of the aldehyde and alcohol. In addition, this benzoic acid derivative exhibits an extended aromatic acid macro group frequency train (b).The macro frequencies are as follows ... 

Aldehydes. The aldehyde functional groups gives rise to several good group frequencies (Table 8.10 also see Chapter 8W, IR section. Fig. W8.25). 

Characteristic group frequencies of aldehydes are shown in Figure 29. Together with the car-... 

Aldehydes have been less extensively studied, but there is a considerable body of evidence to show that the frequency shifts caused by environmental changes are closely parallel to those of ketones. The identification of aldehydes can usually be confirmed by a study of the C—H stretching frequency of the aldehydic group. By virtue of the strong influence of the carbonyl oxygen, this C—H frequency is virtually independent of the rest of the molecule, and is therefore highly characteristic. 

In most cases the frequencies of substituent groups attached to these heterocycles differ little from those observed for their benzenoid counterparts. The only notable exception is the spectral behaviour of carbonyl groups attached to position 2. These have attracted much attention as they frequently give rise to doublets, and occasionally multiplets. In the case of (34), (35) (76JCS(P2)l) and (36) (76JCS(P2)597) the doublets arise from the presence of two conformers (cf. Section 3.01.5.2), whereas for the aldehydes (37) the doublets are... 

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