Other Aldehyde Bands

Saturated aliphatic aldehydes 1740-1720 5.75-5.81 VS w-m General range for saturated compounds (not aliphatic) 1790-1710cm .  

In general, aromatic aldehydes have a strong absorption at 700-580 cm (14.29-17.24pm) due to in-plane deformation vibrations of the C-CHO group.  

Aliphatic aldehydes have a medium-to-strong band at 695-635cm (14.39-15.75pm) and 565-520cm (17.70-19.23pm) due to C-C-C=0 and C-C=0 deformations respectively. 

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The SNIFTIRS results presented here confirm the presence of formic acid and methyl formate as by-products of methanol oxidation. Other by-products such as formaldehyde could not be detected under our experimental conditions. In fact, formaldehyde hydrolyses (99.99%) in aqueous solutions to a gemdiol H2C(OH)2, and the typical aldehyde bands are, therefore, not expected. 

UV-VIS Aldehydes and ketones have two absorption bands in the ultraviolet region Both involve excitation of an electron to an antibonding tt orbital In one called a TT TT transition the electron is one of the tt electrons of the C=0 group In the other called an n ir transition it is one of the oxygen lone pair electrons Because the tt electrons are more strongly held than the lone parr electrons the transition is of... 

Figure 8.34 Strong, sharp absorption at 1700 cm 1 indicating a carbonyl group. No other significant patterns except the C-H pattern on the low side of 3000 cm . It is an aliphatic aldehyde or ketone. Figure 8.35 A benzene ring is indicated because of the band on the high side of 3000 cm-1 and the series of weak peaks between 1700 and 2000 cm . Aliphatic C-H bonds are also indicated (absorption bands on the low side of 3000 cm-1). Possibly ethylbenzene, or a similar structure.

Any conclusions reached after examination of a particular band should be confirmed where possible by examination of other portions of the spectrum. For example, the assignment of a carbonyl band to an aldehyde should be confirmed by the appearance of a band or a pair of bands in the 2900-2695 cm-1 region of the... 

It is now necessary to deduce the nature of the carbonyl function (i.e. whether it is an aldehyde, ketone, ester, etc.). Each of these functional groups (with the exception of ketones) exhibits further characteristic and identifiable absorption bands due to the attachment of atoms other than carbon to the carbonyl carbon atom. Thus an aldehyde should exhibit a double band in the region of 2830-2700 cm-1, due to stretching of the C—H bond in the aldehydic group. A car-... 

When worked up sequentially with sodium bisulfite, sodium bicarbonate, and sodium hydroxide, the noncarbohydrate portion divides into fractions rich in aldehyde groups, carboxyl groups, and free phenolic hydroxyl groups, all exhibiting strong aromatic bands in infrared spectra (Figure 5). A fourth fraction remains after extraction by the other three reagents which shows some hydroxyl and aldehydic functionality but mainly aliphatic hydrocarbon structure. This neutral fraction is derived... 

Most metal carbonyl complexes exhibit sharp and intense CO bands in the range 1800-2100 cm-1. Since the CO stretch motions are rarely coupled with other modes and CO absorption bands are not obscured by other vibrations, measurement of the CO stretch bands alone often provides valuable information about the geometric and electronic structures of the carbonyl complexes. As we may recall, free CO absorbs strongly at 2155 cm-1, which corresponds to the stretching motion of a C=0 triple bond. On the other hand, most ketones and aldehyde exhibit bands near 1715 cm-1, which corresponds formally to... 

These cytochromes contain haem a which differs from the haem of other haem-proteins in that it has an unsaturated substituent, —CHO. In accord with theoretical expectation such a substituent shifts all the absorption bands to lower energy, and increases the intensity of the a/J (especially the a) bands relative to the Soret band. Thus in this series both Fe(II) and Fe(III) haem a complexes have well-pronounced a-bands. The introduction of an aldehyde substituent is also likely to stabilise low-spin as opposed to high-spin states. Thus it is not surprising that magnetic susceptibility data on the cytochromes a show that neither the Fe(II) nor the Fe(III) forms are more than 75% high-spin (133). 

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