In the electromagnetic specter, the region of frequency understood between 3 x 1012 Hz and 4,3 x 1014 Hz corresponds to the infra-red ray (IV). When this radiation is absorbed by a organic composition molecule, occurs ' ' deformaes' ' in the linkings between constituent atoms of the composition. The analysis of a specter gotten for absorption in the infra-red ray is of much value for the study and the briefing of the chemical structure of a substance (either gotten it of a medicine, of a vegetal extract, one shows ambient, of a chemical reaction). The region of the specter understood between frequency 4000 cm-1 and 625 cm-1 presents importance for Organic Chemistry. The deformations suffered for the chemical linkings, in result of the absorption in the infra-red ray, are perceived through vibracionais movements in the linkings, which involve angular deformations (in ' ' ngulos' ' of linkings) axial deformations (in the axles of the linkings). Of this form, the movements are found: stretching (symmetrical and anti-symmetrical), shears, twist, wag and rotation. In the Co2 molecule (carbonic gas), are verified angular deformation (= C =) in frequency 667 cm-1, while in the water molecule, occur angular deformation of linkings (H? H) in frequency 1595 cm-1.

Can be verified symmetrical axial deformation in the linkings of (H? H) in 3655 cm-1 and anti-symmetrical in 3755 cm-1. In this last case, in the water molecule, it is calculated that the axial deformation of each linking? H, corresponds to the frequency 3700 cm-1, a value ' ' intermedirio' ' between the two last ones. For Organic Chemistry, it does not interest the analysis ' ' complete and detalhada' ' of specters IV, many bands of absorption are ' ' desconhecidas' ' or they are ' ' desprezadas' ' , however frequencies of absorption of functional groups that matter, in the structural briefing, are taken in consideration, being compared with gotten data of other specters (others techniques) and with one ' ' biblioteca' ' data base of standards previously analyzed.