There are many types of crystalline substances, which can be divided into different types depending on the type of particles on the lattice nodes and the interaction between the particles. From the perspective of stereochemistry, crystals can be classified into two broad categories, optically active, and not optically active. Like an optically active compound, if there is a heavy anti-axis S1 (a symmetry anti-axis, ie, a symmetry plane), a double anti-axis S2 (ie, a symmetry center), a quadruple anti-axis S4 or higher When the axis is, the crystal is not optically active. If there are no above symmetry factors, it is optically active. That is, the arrangement of the particles in the crystal is achiral, and it does not have optical activity, and if it is chiral, it has optical activity. The crystal is observed macroscopically. If it is optically active, the crystal form of the crystal is chiral. If it is not optically active, the crystal form of the crystal is achiral. Of course, only the transparent chiral crystal can observe its optical activity. Viewed from the microstructure of the optically active crystal, the particles are arranged in a spiral shape. The crystal face threads of some crystals can be clearly observed under the microscope. Optical homes have long found that when the particles in the crystal are arranged in the form of right-handed spirals, the crystals are right-handed. If arranged in the form of a left-handed spiral, the crystal is left-handed (as shown below). On the left is the right hand spiral and on the right is the left hand spiral Since the plane polarized light is composed of a combination of left-handed circularly polarized light and right-handed circularly polarized light. When plane polarized light is incident on an anisotropic crystal. The refractive indices of the two circularly polarized lights are not equal. The difference in refractive index is essentially due to the difference in the propagation speed of the two circularly polarized light in the crystal. When the crystal is transmitted, the two kinds of circularly polarized light are not synchronized. When they are recombined into polarized light, they are changed to elliptically polarized light, and the plane of polarization will produce an angle change. This angle is the optical rotation of the crystal. The polarization is rotated to the right, called right-handed, and is represented by "+". The polarization is rotated to the left, called the left rotation, and is represented by "-". In order to compare the optical rotation ability of various crystals, it is necessary to exclude the factors affecting the optical rotation measurement such as crystal thickness, crystal concentration, and wavelength of light. Therefore, the optical rotation is converted into specific optical rotation (that is, optical rotation at unit density and unit thickness). [a]D20=a/(l*d) In the formula: The specific optical rotation of different crystals is different. Thus, there is a comparable standard for the optical rotation of various crystals. When plane polarized light passes through the crystal in different directions, the optical rotations differ greatly, which reflects the various properties of the crystal. Each crystal has a maximum optical rotation. When comparing the optical rotation of various crystals, the maximum optical rotation should be used, otherwise the comparison will lose its meaning. The anisotropy of the crystal is different from the optically active solution and liquid, and the spiral direction in the solution and liquid is arbitrary. Therefore, its optical rotation is independent of the direction of the incident light. Macroscopically, solutions and liquids are isotropic, but microscopically anisotropic. Classification of optically active crystals Optically active crystals can be classified into two classes, one that does not exhibit optical activity in solution and the other that exhibits optical activity in solution. A common feature of these two types of compounds is that the particles in the crystal are arranged in a spiral shape. In general, because the crystal is rigid, the molecular conformation in the crystal exists in the most stable single conformation. The spiral direction inside the crystal is fixed, and the orientation of the spiral is also fixed. A spiral multi-turn spiral in the crystal. For these reasons, the maximum optical rotation of the crystal is always much larger than the specific optical rotation of the solution and gas of the same composition. Since the molecules in the solution are disorderly arranged, the total optical rotation direction and size of the solution are determined by the algebraic sum of the helix and the right helix of various orientations, so the optical rotation is generally small. The crystal directions of the same substance and the optical rotation direction of the solution are not all the same. The main optical rotation direction of the crystal is determined by the spiral direction of the crystal. Wiping Sticks And Cotton Swabs Reusable Cotton Swab,Reusable Cotton Buds,Sterile Cotton Swab,Cotton Applicator Hunan Kangfutai Medical Devices Co., Ltd. , https://www.3kfut.com
[a]--specific optical rotation, 20 means measured at room temperature 20 degrees Celsius, and D means sodium light D line 589 nm.
a--The actual measured optical rotation.
l--The thickness of the crystal through which light passes, in units of dm.
d--The density of the crystal, in units of g*cm-1.