NMR Analysis Virtual Lab Simulation | PraxiLabs

NMR Analysis Virtual Lab Simulation

Chemistry | Analytical Chemistry



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General Aim

Analyzing pesticides in a water sample.

Method

Different pesticides will be analyzed for their chemical structure using proton NMR. Each sample is dissolved in deuterated chloroform, and purified before analysis. Through analysis: The number of signals.*The chemical.

Learning Objectives (ILO’s)

  • Become proficient at basic concepts of chemical characterization of chemical compounds.

  • Learning basics of spectrometry techniques.

  • Understand mechanism of operation of proton NMR.

  • Learn functions of NMR in chemical compounds analysis.

Theoretical Background/Context

Nuclei with odd atomic (number of protons) or mass number (total number of protons and neutrons) or both have quantized spin angular momentum and a magnetic moment. Interaction of the magnetic moment of an atomic nucleus (µ) with an external magnetic field results in absorption of energy and change their spin orientation with respect to the external field. NMR gives the chemical properties of molecules by studying the magnetic properties of the atomic nuclei which is measured by resonant absorption by nuclei.
The electrons around the nucleus shield the nuclei from effective magnetic field and requires energy of lower frequency to cause resonance. Therefore different nuclei in the same compound come into resonance at different frequencies. In general hydrogens bound to carbons attached to electron withdrawing groups tend to resonate at higher frequencies. The position of where a particular hydrogen atom resonates relative to TMS is called its chemical shift.
Chemical Shift: Nuclei in a different chemical environment experience different magnetic field. The electron cloud around the nuclei induces electronic angular momentum which gives rise to an additional magnetic field ß.
Solvent and internal standard:
Tetramethylsilane is used as an internal standard during the NMR measurements for the following reasons:

  1. Is inert, nontoxic, low boiling point and can be recovered by distillation
  2. Very small amount is required for measurement
  3. Has 12 equivalent protons and thus give a single strong peak
  4. The signal appears outside (more up field) away from most of the protons signals

When using the modern NMR instruments, no internal standard is added to the sample to be measure. The difference between the solvent signal and the TMS is known. The modern instruments detect the solvent signal and lock them, which now can serve as the internal standard.

Principle of Work

Different pesticides will be analyzed for their chemical structure using proton NMR. Each sample is dissolved in deuterated solvent and purified before analysis. For a non-polar to moderately polar compounds deuterated chloroform is commonly used. For polar compounds deuterated Dimethyl sulfoxide (DMSO) is commonly used. An NMR spectrum gives various information of the compound to helps in structural elucidation of the organic molecule e.g.:

  1. The number of signals that gives the  number of different sets of protons present in the sample measured.
  2. The chemical shift that gives the environment of the protons.
  3. Multiplicity that gives information on the number of protons on adjacent atoms, and integration of the peaks (peak area) that gives the number of protons in each environment.

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