The science of chemistry is divided to multiple of branches and one of them is the Organic chemistry which focuses on the compounds that contain carbons. “Functional groups are collections of atoms in organic chemistry molecules that contribute to the chemical characteristics of the molecule and participate in predictable reactions”(Helmenstine,2018).
Alcohols are functional groups that identified by the existence of an (-OH) group. Ethers are one of the organic compounds that is defined by the connection of an oxygen atom with two alkyl or aryl groups and they are generally written (R-O-R`).
It’s good to mention that R and R` stands for both any alkyl group or groups. Aldehydes and ketones are organic compounds that consist of a carbonyl Group (C=O). Carboxylic acids are organic acids which contain a (-COOH) group. Another functional group is ester which is produced from the reaction between alcohols and carboxylic acid having the structural formula (RCOOR`). Esters are derivatives of carboxylic acids because when it hydrolysed, they give a carboxylic acid.
Amines are detected by the existence of a nitrogen atom, a lone pair of electrons, and three substituents and the general form of it is (R-NH2).
The electromagnetic spectrum is the collective name for all types of radiation. Radiation is energy that travels around in waves. The electromagnetic spectrum goes from the waves with the lowest energy to those with the highest energy.
Those functional groups are detected by IR (infrared) spectroscopy as each functional group have specific bonds which show up every time in the exact place in the IR spectrum.
Sir William Herschel was the first to recognize the existence of infrared in 1800. Interest in IR was not explored further for 80 years. During 1882-1900 several investigations were made into the IR region. Abney and Festing photographed absorption spectra for 52 compounds and correlated absorption bands with the presence of certain organic groups in the molecule (Smith).
W. W. Coblentz laid the real groundwork for IR spectroscopy. Starting in 1903 he investigated the spectra of hundreds of substances, both organic and inorganic. His work in the rock salt region, from 0.7 to 18 (m, was so thorough and accurate that many of his spectra are still usable. The experimental difficulties of the early researchers were many. They not only had to design and build their own instruments but all the components too. Obtaining a spectrum was a tedious job requiring 3-4 hours or more since each point in the spectrum had to be measured separately and at least 10 points per micrometer were measured. After World War II advances in electronics made it possible to obtain a spectrum in 1-2 hours (Smith).
The end result of this early work was the recognition that each compound had a unique IR spectra and that certain groups, even when they were in different molecules, gave absorption bands that were found at approximately the same wavelength.
The IR absorption spectrum of a compound is its most unique physical property. The samples can be liquids, solids, or gases. They can be organic or inorganic. The only molecules transparent to IR radiation under ordinary conditions are monatomic and homonuclear molecules such as Ne, He, O2, N2, and H2. One limitation of IR spectroscopy is that the solvent water is a very strong absorber and attacks NaCl sample cells.
In terms of a comparison of physical properties, a melting point, refractive index, or specific gravity gives only a single point of comparison with other substances. An IR spectrum, in contrast, gives a multitude of such points. Not only can the position of bands be compared but their intensity as well since the intensity is indicative of the number of a particular group contributing to an absorption. IR is usually preferred when a combination of qualitative and quantitative analysis is required. It is often used to follow the course of organic reactions allowing the researcher to characterize the products as the reaction proceeds
Figure two: a picture of a FTIR spectrophotometer that produces infrared absorption spectrum by identifying chemical bonds in a molecule
00Figure two: a picture of a FTIR spectrophotometer that produces infrared absorption spectrum by identifying chemical bonds in a molecule
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