Structural experiments for the determination of ethylbenzene by nuclear magnetic resonance spectroscopy
Structural experiments for the determination of ethylbenzene by nuclear magnetic resonance spectroscopy
This experiment is from the official website of Wuhan University School of Pharmacy
Operation method
Structural experiments for the determination of ethylbenzene by nuclear magnetic resonance spectroscopy
Principle
Atomic nuclei can be viewed as spheres with uniformly distributed nuclear charges and spin like a gyroscope, with magnetic moments generated, and are the main object of NMR studies. A nucleus with a non-zero magnetic moment has a nuclear spin. The size of the resulting nuclear magnetic moment μ is related to the angular momentum in the direction of the magnetic field P: μ = γ P where γ is the magnetic spin ratio and each nucleus has its fixed value. Moreover, P = mh/2π or μ = mγh/2π where h is Plank's constant (6.624 × 10-27 erg.s); m is the magnetic quantum number, the magnitude of which is determined by the spin quantum number L, with a total of 2L + 1 values of m, or, in other words, there are 2L + 1 states of the angular momentum P. It is important to note that in the absence of an applied magnetic field, the nuclear energy levels are simple and merge, and the states have the same energy. For the hydrogen nucleus, L = 1/2 and its m-value can have only 2 × 1/2 + 1 = 2 orientations. +1/2 and -1/2, indicating that the H nucleus, in a magnetic field, has only two orientations of the spin axis: a) in the same direction as the applied magnetic field, m = +1/2, with a lower magnetic energy level; and b) in the opposite direction of the applied magnetic field, m = -1/2, with a higher magnetic energy level; in a strong magnetic field, the energy levels of the nuclear spins will split. The split energy level is small: e.g., in a 1.41T magnetic field, the magnetic energy level difference is about 25 × 10-3 J. When absorbing external electromagnetic radiation (4~900MHz), a jump in the nuclear energy level will take place - generating the so-called nuclear magnetic resonance (NMR) phenomenon. That is: radiofrequency radiation → atomic nuclei (strong magnetic field, energy level splitting) → absorption → energy level jump → NMRNMR through the study of atomic nuclei on the absorption of radiofrequency radiation, in order to a variety of organic and inorganic composition, structure, qualitative analysis, and sometimes quantitative analysis can also be carried out. For example, in determining the structure of organic compounds, the position and intensity of the proton resonance (1H NMR) signal and its splitting are used to determine the position of hydrogen atoms, their environment, and the relative number of H atoms in functional groups and the C skeleton. Similar to UV-vis and infrared spectroscopy, NMR also belongs to absorption spectroscopy, except that the object of study is the absorption of radiofrequency (RF) radiation by nuclei of atoms in a strong magnetic field. When the sample is irradiated by a broadband RF signal, the total magnetization vector of the sample deviates from the equilibrium state. After disconnecting the RF radiation, the magnetization vector gradually returns to the equilibrium state (relaxation) while generating an induced electromotive force, i.e., free induction decay (FID). It is characterized by a point-height signal that decreases with time, which is then Fourier transformed to obtain the intensity versus frequency curve, known as the NMR spectrogram.
Materials and Instruments
nuclear magnetic resonance (NMR) instrument Move 1. Preparation of sample solution: Prepare a deuterated chloroform solution of ethylbenzene with a concentration of about 0.01 mol-L-1 and fill the NMR sample tube. Common Problems 1. Analyze the resulting plots. For more product details, please visit Aladdin Scientific website.
2. Sample detection was realized in the operation platform of PC.