Molar refractive index

Physical terms

Molar refractivity is due to light Under the irradiation of molecule in Electronic cloud (Mainly valence electron ）Relative to Molecular skeleton Of relative motion Results, usually with symbols R express. Molar refractive index can be used as electron in molecule Polarizability Measurement of. Molar refractivity is generally Abbe refractometer determination; The calculation method can also be used, that is, according to the characteristics and connectivity of the groups in the molecule, the group contribution method and the topological method can be organically combined Alkyne Molar refractivity of and molecular structure Quantitative relationship between.

Chinese name: Molar refractive index
Foreign name: molar refractivity

expression: R =( n ^2-1)/( n ^2+2)· M / ρ
Applied discipline: optics

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Molar refractivity is due to light Under the irradiation of molecule in Electronic cloud (mainly valence electrons) relative to Molecular skeleton Of relative motion The result of the R express. Molar refractive index can be used as electron in molecule Polarizability A measure of Definitional expression For: R =( n two -1)/( n two +2)· M / ρ 。 among n by Refractive index ； M by Molar mass ； ρ by density 。 Molar refractivity and wavelength Relevant, if Sodium light D Line Is a light source (of High frequency electromagnetic wave ， λ =5893 Ǻ), the measured refractive index is n D Represents the corresponding molar refractivity as R D express. according to maxwell (James Clerk Maxwell) Electromagnetic field theory , physical Dielectric constant ε And refractive index n The relationship between them is as follows: ε ( λ )= n two ( λ ）, i.e ε and n Average and wavelength λ of Substitute the above formula to get the definition formula of molar refractivity.

The meaning of molar refractivity is that it has Additivity , that is, the molar refractive index of a molecule is equal to Chemical bond Of Refractivity The sum of. For example: Trichloromethane Molecular (CHCl three ）It includes one carbon hydrogen bond (C-H) and three carbon chlorine bonds (C-Cl). The molar refractive index of the molecule is the sum of all bond refractive indexes, that is R = R C-H +3 R C-Cl =（1.676+3×6.51）cm three /mol=21.21cm three /mol。 This calculated value is compared with the experimental measurement results, so that it can be determined chemical compound Of structure It can also be used to identify compounds and analyze mixture The composition of.

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Molar refractivity is determined by Abbe refractometer Determined. New methods include calculation, that is, according to the characteristics and connectivity of groups in molecules, the group contribution method and topological method are organically combined Alkyne Molar refractivity of and molecular structure Therefore, a method to calculate the molar refractive index of hydrocarbon directly from the molecular structure is developed. This method has wide application scope and topology The calculation results of the method are reliable. For 84 kinds of hydrocarbon (C five To C forty ）The calculated results show that the calculated values of molar refractivity are in good agreement with the experimental values, and the average error is only 0.011%. For details, please refer to the article Calculating the Molar Refractivity of Alkynes by QSPR Method.

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