UV spectral absorption bands of classification
1 , far ultraviolet ( VUV ) absorption band with a relatively small this should be very small, usually UV spectrophotometer from 200 nm wavelength is started , because the far- ultraviolet ( VUV ) absorption band is strongly absorbed by air , by definition, also called vacuum ultraviolet . The main absorption band alkane compounds , such as CC, CH groups as δ → δ * transition , the maximum absorption wavelength of less than 200 nanometers , in the range of 10-200 nm.
2, the end of the saturated halogenated hydrocarbon absorption band absorption with a single bond or a hetero atom-containing amine compound , since such compounds containing one or more lone pair of electrons, resulting n → δ * transition , which is far from the range of end of the near-ultraviolet region to the ultraviolet region near 200 nm. So, usually in the ultraviolet region scan or full wavelength scans , it is recommended to start from 210 nanometers , because many substances are present end absorption , multi- sweep not make much sense , considering the deuterium lamp from saving time and perspective , it is recommended to start from 210 nanometers scanning.
3, R absorption band belongs to the weak absorption band , but the solvent effect is more obvious , so I remind this friendship , the choice of solvent must pay attention to Oh . R molecule conjugated with a heteroatom-containing group absorption band , such as C = O, N = O, N = N and the like groups , n → π * transition has generated weak absorption band , the molar absorption coefficient K Average less than 100L.mol-1.cm-1; with increasing solvent polarity , R band blue shift occurs , a strong absorption band near the subject , will redshift when R with , sometimes not observed .
4, K with the use of more, but also on the basis of qualitative and quantitative analysis of organic matter , and its maximum absorption is often determined by the K band , in general , if a physical presence of conjugated double bonds , in theory can be used to the ultraviolet to qualitative and quantitative , so I suggest that you pay special attention to K band Yeah. Conjugated system of the π → π * transition of the absorption band generated , such as conjugated olefins, ketene . K band absorption intensity is high , generally greater than K 10000L.mol-1.cm-1.
5, B with theoretical support : aromatic and heterocyclic compounds π → π * characteristic absorption band . B benzene absorption band between 230-270 nm, and the emergence ( which is why there is bread peak ) contains multiple peaks or broad absorption band fine structure . However, B -substituted aromatic hydrocarbons with fine structure disappears , the polar solvent may also cause the fine structure disappears.
6 , benzene -containing material with a generally E B and E with band absorption , but did test , I feel much K absorption band B with strong , sorbic acid and benzoic Take for example, the same concentration of sorbic acid particularly strong absorption maximum absorption is obvious , but the bread was like acid peak , maximum absorption especially obvious, only to find out through the derivation of maximum absorption ability, more depressed . This can also be seen from the absorption coefficient , absorption coefficient B band of 250-300 L.mol-1.cm-1, the feeling is not very sensitive. E with a large absorption coefficient , E and B but the effect is often not very good peak shape is not conducive to analysis . Aromatic structures are also characteristic absorption in the three cyclic conjugated ethylenic bonds benzenoid System π → π * transition generated . E band is divided into E1 and E2 bands. Are strong absorption band with E , K is greater than 10000 L.mol-1.cm-1