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Characterization Techniques CHEM241-03A - Coggle Diagram
Characterization Techniques CHEM241-03A
Melting Point
Overview
What does it do?
It helps to determine the purity of an organic compound.
When is it used?
When comparing solid mixture's melting point to a pure molecules
How does it work?
The actual melting point range of the unknown must be obtained.
The unknown is then combined with each of the different sample unknowns that are given, each mixture melting point is recorded.
Given that the unknown should be one of the compounds. The melting point range should be the same as the pure unknowns melting point range.
If the mixture does not contain the same compound then the range would be wider.
Pros and Cons
Pros:
Easy
Time Efficient
Cons:
Easy to pass boiling point with manual temperature knob.
Sample must be solid
Video
https://www.youtube.com/watch?v=9RNRYLvlbXM
Thin Layer Chromatography :
Pros and Cons
Pros:
-minimal equipment.
-have the ability to run multiple samples at one time on a plate/paper.
-creates extremely accurate results
low percent error while using thin layer chromatography.
-works great with small samples
There are two different ways to review results: you can use colorimetric detection or the UV light which we used in class.
Cons:
-Cannot tell the difference between isomeric and enantiomeric forms of a compound.
-Unable to define a distinction between chiral molecules.
-Rf value has to be known prior in order to know what your looking for.
-Results can be thrown off by environmental factors such as humidity and temp
Overview:
How Does is work?
-Thin layer chromatography works by using a thin, uniform layer of silica gel or alumina coated onto a piece of glass, metal or rigid plastic.
The silica gel (or the alumina) is the stationary phase. The stationary phase for thin layer chromatography also often contains a substance which fluoresces in UV light
What does it do/ When is it used?
-Thin Layer Chromatography is a chromatography technique used to separate non-volatile mixtures.
-monitor the progress of a reaction, identify compounds present in a given mixture, and determine the purity of a substance.
-Thin layer Chromatography has a stationary phase which separates (solids, or liquid supported on a solid). There is also a mobile phase The mobile phase flows through the stationary phase and carries the components of the mixture with it. Different components travel at different rates.
Analyzing Data:
-You can analyze the Thin Layer Chromatography data by calculating the Rf values
-Rf= (Distance the spot traveled/Distance solvent traveled)
-You can also verify unknown through double spotting or co-spotting techniques
Video
https://youtu.be/qdmKGskCyh8
Gas Chromatography
Video
https://www.youtube.com/watch?v=4Xaa9WdXVTM&t=15s
Pros and Cons
Pros:
-Allows us to quantify how many compounds are in a given mixture and the amount that each compound makes up in the total mixture
-Can calculate g of each component, percent yield of the product, and percent unreacted starting material
-Technique allows mixtures to be separated relatively quickly
-Accurate
Cons:
-Must only use volatile and thermally stable mixtures
Overview
What is it?
-Separates mixtures based on their differences in polarity and their affinities for a stationary and mobile phase
-Compounds with a low affinity for the resin travel quickly through the column and compounds with a high affinity travel slowly
-Used with volatile mixtures
How does it work?
-Utilizes a thin column that acts as a fractional distillation column
-The molecules travel through the column at different speeds so they can be separated
-A small amount of sample is injected into the gas chromatograph and moves through the column, being separated into components; they are detected as they exit the column and are displayed on a GC chart that can be analyzed
Analyzing GC charts
-Different peaks correspond to different compounds, with Rf (retention time) referring to the time it takes for each compound to exit the column
NMR Spectroscopy
Pros and Cons
Pros:
allows for analyzing identity
-allows view of molecular dynamics
-sample stays intact for future use
Cons:
may have peaks from other solvents that were present
Video
https://www.youtube.com/watch?v=SBir5wUS3Bo
Overview
Analyzing data
Pick an sp3-hybridized carbon atom to analyze.
Note if a CH3 group, a CH2 group, or a CH group and determine base chemical shift value using the table.
Note the substituents attached to the α-carbon and determine chemical shift values.
Add these values together to get the predicted chemical shift value for that hydrogen.
The actual value will be ±0.2 ppm due to margin of error.
By comparing the predicted values to the actual NMR spectra which constitutional-isomer products is more present in the product can be determined.
How does it work?
The chemical shift is the x-axis value of each signal.
The integration is the area under the curve of each signal.
The ratio of areas under each signal is proportional to the number of hydrogen atoms represented by that signal.
A molecule is placed inside a
strong magnet and irradiated with low energy using radio wave photons.
Energy will be absorbed based on the amount of electron density around the nucleus of a hydrogen atom.
The results provide information about the structure of the molecule.
What does it do/ When is it used?
NMR spectroscopy analyzes the various protons in a molecule and results give information about the structure of the molecule.
It provides the number of signals, the chemical shift of each signal, the integration of each signal, and the splitting pattern.
The identity of a product can be determined using NMR spectroscopy.