溶液法测定极性分子的偶极矩（Determination of dipole moment of polar molecule by solution method）Determination of dipole moment of polar molecule by solution method
I. objectives and requirements
Determination of dipole moment of ethyl acetate by solution method
Understand the relationship between dipole moment and molecular electrical properties
The experimental technique of measuring dipole moment by solution method
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The basic principles of I I.
Dipole moment and polarizability
The molecular structure can be approximated by stone and is made up of electrons. And for the skeleton (nuclei and inner electrons). Becau of the different configurations of molecular space, the centers of positive and negative charges may coincide or overlap. The former is called nonpolar molecule, and the latter is called polar molecule.
Fig. 1 electric dipole moment indication
In 1912, Debye (Debye) propod the concept of dipole moment
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Mu to measure the magnitude of molecular polarity, as shown in Figure 1一秒泪崩的句子
EMBED Equation.3 (1)
In the formula, q is the charge of the positive and negative charge centers, D is the distance between the positive and negative charge centers, and Mu is a vector who direction is from positive to negative. The order of magnitude of the dipole moment is EMBED, Equation.3, C, m, becau the magnitude of the distance between atoms is EMBED, Equation.3, m, and the order of charge is EMBED, Equation.3 and C.
Through the determination of dipole moment, we can understand the distribution of molecular cloud and symmetry of molecules in molecular structure, and also can be ud to distinguish the geometric isomer and the three-dimensional structure of molecules.
Polar molecules have permanent dipole moments, but becau of the thermal motion of molecules, the dipole moment has the same chance of pointing in all directions, so the dipole moment is equal to zero. If the polar molecule is placed in a uniform electric field, the dipole moment will tend to the el
ectric field in the direction of the electric field. At this point we call the molecules polarized, and the degree of polarization can be measured by the molar polarization EMBED Equation.3.
The EMBED Equation.3 is proportional to the square of the permanent dipole moment and inverly proportional to the thermodynamic temperature T
EMBED Equation.3 (2)
In the formula, K is the Boltzmann constant and L is the A Vogadero constant.
In the external electric field, regardless of polar molecules or non polar molecules will occur relatively mobile electronic cloud on the molecular skeleton, the molecular skeleton will deform, this phenomenon is called polarization or polarization induced deformation, to measure the polarization EMBED Equation.3 induced by moore. Obviously, EMBED Equation.3 can be divided into two, namely electronic polarization EMBED Equation.3, EMBED Equation.3 and atomic polarizability, so EMBED Equation.3 = EMBED Equation.3 + EMBED Equation.3. EMBED Equation.3 is directly proportional to the external electric field strength and independent of temperature.
If the external electric field is an alternating electric field, the polarization of the polar molecule is rela
小学数学教师论文ted to the frequency of the alternating field. When the frequency is lower than EMBED, Equation.3 and S-1 in the low frequency electric field or electrostatic field, the polarization polarization P produced by polar molecules is the sum of the steering polarization, the electron polarization and the atomic polarization
EMBED, Equation.3 = EMBED, Equation.3 + EMBED, Equation.3 + EMBED, Equation.3 (3)
When the frequency is incread to EMBED Equation.3 to EMBED
Equation.3 S-1 (infrared frequency), electric field alternating period is less than the molecular dipole moment of relaxation time, change of steering movement of polar molecules with no electric field, the polar molecules can along the electric field direction, so the EMBED Equation.3 = 0. At this time, the molar polarization of polar molecules is equal to the molar induced polarization degree EMBED Equation.3. When the frequency of alternating electric field further incread to more than EMBED Equation.3 S-1 high frequency (visible light and ultraviolet frequency), change to the movement and deformation of the molecular skeleton could not keep up with the polarity of the electric field of the molecule, the molar polarization of polar molecules is equal to the electronic polarization of EMBED Equation.3.
Therefore, in principle, as long as the low frequency electric field measured polar molecules molar polarization in P, infrared frequencies measured Moore polar molecules induced polarization of EMBED Equation.3 Moore, obtained by subtracting the two polar molecules to the degree of polarization of EMBED Equation.3 generation (2), then you can type permanent dipole moment. To calculate the molecular polarity.
Two. Determination of polarizability
Clausius mosotti Debye, and (Clausius Mosotti Debye) the relationship between molar polarization P and dielectric constant from electromagnetic theory
EMBED Equation.
3 (4)
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In the formula, M is the molar mass of the analyte, P is the density of the material, e can be determined through experiments.
But (4) is deduced from the assumption that the molecules do not interact with each other, so it is only applicable to the system with low temperature. However, it is difficult to determine the dielectric
constant and density of the gas pha, and some substances can not even make it in a stable gas pha. Therefore, a solution method was later propod to solve this difficulty. The basic idea of solution method is that in a nonpolar solvent solution of infinite dilution in the state, and the solute molecule is similar, so the molar polarization EMBED Equation.3 infinite dilution of the solute can be regarded as a type of P (4).
Hyde (Hedestran) firstly, Zittrain approximate formula of dilute solution
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EMBED Equation.3 (5)
EMBED Equation.3 (6)
Bad on the additivity of the solution, the formula for the molar polarization of solute in infinite dilution is derived
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我找工作EMBED Equation.3 (7)
