One, absorption spectrum
Absorption spectrum, "absorption spectrum," refers to the material absorption of photons, from the low energy level to the high energy level of the spectrum. The absorption spectrum can be linear or absorption band. The study of absorption spectrum can understand the structure and motion of atoms, molecules and many other substances, and how they interact with electromagnetic fields or particles. Absorption spectrum, also known as absorption curve, refers to the absorbance of A substance (or transmittance T) with the wavelength λ change curve.
The absorption spectrum reflects the distribution of light absorption capacity of light-absorbing substances in different spectral regions. The number, intensity, position and waveform of wave peaks displayed provide important information about the internal structure of the substances. The characteristics of the absorption spectrum can be described in the following terms.
① The absorption peak →λ Max
The maximum value on the absorption curve is the absorption peak, and the corresponding wavelength is the maximum absorption wavelength λ Max.
② Absorption valley →λmin
The minimum value between peaks is called a valley, and the corresponding wavelength is the minimum absorption wavelength λmin.
(3) the acromion - lambda sh
Next to the absorption peak, there is a zigzag called the acromion with the corresponding wavelength λsh.
④ Terminal absorption → saturation σ-σ transition occurs
At the short wave end of the absorption curve, strong absorption without peak shape is called terminal absorption.
Two, chromophore and chromophore
Chromophore refers to the group that can absorb uV-visible light and produce electron transition. The chromophore of organic matter is mainly the group that can produce π-π* or n-π* transition. The main ones are: -c =O, -n =N-, -n =O, etc. However, only simple double bond compounds chromogenic effect is limited, it may sometimes still in the far ultraviolet region, if the molecule has alternate single double bond "conjugated π bond" (delocalized bond), such as: CH2=CH -- CH=CH2. Because the electrons in the large π bond move in the whole molecular plane, the activity increases, so that the energy difference between π and π* is reduced, so that the absorption peak of π- π* is shifted long, and the color effect is greatly enhanced.
The functional group which is not "chromophore" itself, but can enhance the chromophore chromophore effect - is called chromophore, refers to heteroatomic saturated groups containing non-bonded electrons, mainly include: -- OH, -- NH2, -- SH, -- Cl, -- Br, etc.
These groups, when present alone, generally do not absorb uv - visible radiation. But when they are combined with the chromophore group with orbital, they will make the absorption wavelength of the chromophore long shift (red shift), and make the absorption intensity increased.
Three, red shift and blue shift
The wavelength of the absorption peak shifts due to the structural change of the compound or the influence of the solvent, and the phenomenon of moving to the long wavelength direction is called red shil, also known as long bathochromic shift. The phenomenon of moving in the short wavelength direction is called blue shift, also known as hypsochromic shift.
Four, add color effect and subtraction effect
Hyperchromic effeet (HYPERchromic effeet) occurs when the absorption intensity of a compound increases due to structural changes or other reasons. Conversely, a decrease in absorption is called the hypochromic effect or hypochromic effect.
Strong and weak b