This experiment is from the official website of College of Chemistry, Qingdao University of Science and Technology.
Operation method
nuclear magnetic resonance hydrogen spectroscopy (NMRH) experiment
Principle
1, the concept of nuclear magnetic resonance has a magnetic nucleus, in an applied static magnetic field, by the action of a specific frequency of electromagnetic waves, in its magnetic energy levels between the resonance of the phenomenon called nuclear magnetic resonance phenomenon. 2, nuclear magnetic resonance resonance conditions ①: the nucleus of an atom with magnetic properties. (γ: the magnetic spin ratio of a certain nucleus) ②: the applied static magnetic field (H0)). ③: a certain frequency (υ) of the radio frequency pulse. ④: formula: 3, the concept of chemical shift and the production of the concept of nuclear magnetic resonance can be seen: the same type of atomic nucleus resonance frequency is the same, here refers to the bare nucleus, did not take into account the chemical environment in which the nucleus is located, in fact, when the nucleus is in a different group (both the different chemical environments), the magnetic field felt by them is not the same. Nuclear magnetic resonance conditions for: due to the existence of different groups of extra-nuclear electron cloud, the atomic nucleus has a certain shielding effect. The induced magnetic field produced by the cloud of electrons outside the nucleus in an applied static magnetic field is: H' = -σH0σ: known as the magnetic shielding constant. Atomic nucleus actually feel the magnetic field is the superposition of the applied static magnetic field and the magnetic field generated by the electron cloud: H = H0 - H'= H0 - σH0 = (1 - σ)H0 So, the actual resonance frequency of the atomic nucleus for: for the nucleus of the same element, if in a different group (both the chemical environment is different), the nucleus of the electron cloud density around the nucleus is not the same, and thus the The resonant frequency υ is different, thus giving rise to a chemical shift. Chemical shift (δ) is defined as: 4, nuclear magnetic resonance spectrometer mode of operation ①: continuous wave mode of operation is divided into two modes of operation: fixed magnetic field, change the frequency of the frequency operation and fixed frequency, change the magnetic field of the swept field mode. ②: pulse wave mode of operation of electronic knowledge can be seen: a pulse wave unfolding in the frequency domain is covered by a certain frequency range of a frequency band, that is to say: a pulse is equivalent to a very short period of time to send out all the frequencies, so that all the nuclei within the frequency range of the simultaneous resonance. The energy released by the nuclei returning from the high-energy state to the low-energy state is then simultaneously detected for each nucleus with different chemical environments.
Materials and Instruments
CDCL3 Ethylbenzene Move 1. Requirements for sample tubes Figure 2.1: NMR Data Acquisition Wizard Diagram Figure 2.2: New Experiment Settings dialog box ③: Channel Settings Figure 2.4 Solvent Selection dialog box. For more product details, please visit Aladdin Scientific website.
AV-500 Nuclear Magnetic Resonance Instrument The sample tubes for NMR are specialized sample tubes.
The sample tube of nuclear magnetic resonance is a special sample tube, which is made of good quality temperature-resistant glass, or made of quartz or polytetrafluoroethylene (PTFE) material. The sample tube is required to be non-magnetic, with straight walls and uniform thickness.
The shape of the sample tube is cylindrical, and the diameter of the sample tube depends on the type of the spectrometer probe, and the outer diameter can be as small as 1mm or as large as 25mm. 5mm, 10mm, and 2.5mm are the common sample tube diameters. The length is required to be greater than 150mm.
The sample tubes used in this instrument are 5mm.
2. Sample Preparation and Requirements
Since NMR is a qualitative analysis method, there is no strict requirement for the sample drift, the sampling principle is: in the case of meeting the analytical requirements, the sample volume is less good, the sample concentration is too large, the rotating side bands or satellite peaks are too large, and the resolution of the spectra deteriorates, which is not conducive to the analysis of the spectra.
Take about 5mg for solid samples and 0.05ml for liquid samples.
Put the sample into the sample tube carefully and inject 0.5ml of CDCL3 (deuterated chloroform) into the sample tube with a syringe to fully dissolve the sample. The sample and reagent should be mixed thoroughly, and the solution should be clear, transparent and free of suspended matter or other impurities.
3、 Turn on the machine
①: Turn on the power of the computer and enter the corresponding power-on password.
②: Run the CCU monitoring program.
③: Turn on the power of the cabinet, general power supply → BSMS/2 power supply → BLAX300/1 power supply → BLAX300/2 power supply → AQS power supply.
④: Enter NMR program: double click: desktop TOPSPIN3.1.
⑤: Initialization: Type: CF↙
The instrument performs self-test and initial state setting.
The standard sample is placed in the magnetic field.
①: Place the standard sample in the magnet (refer to step ①, ②, ③ and ④ in step 6).
②: Access the previously made spectra, type: ii↙. Initialize the sampling parameters.
5. Instrument Status Adjustment
①: Open the Acquisition Guide: click the menu: Spectrometer/DATA Acquisition Guide. the following figure 2.1 appears: 
②: New Experiment Setup
Click: 
(or type the command NEW↙) to design a new experiment. Figure 2.2 below appears: 
Click: 
(or type the command ↙) to observe the sampling channel and deuterolock channel, and Figure 2.3 below appears:
Figure 2.3 Viewing the Sampling Channel and Deuterium Lock Channel
④: Lock Field
Click: 
(or type the command LOCK↙) to lock the magnetic field and Figure 2.4 below appears:
Select CDCL3 (deuterated chloroform) and click OK. The spectrum is automatically homogenized.
⑤: Probe Tuning
