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| Name | What is optical activity of organic compounds?(haloalkane and haloarenes) |
| Video Uploader | Video From TOMAR CHEMISTRY TUTORIAL |
| Upload Date | This Video Uploaded At 12-05-2018 11:17:49 |
| Video Discription | Optical Activity Optical activity of an organic compound refers to the property of an organic compound by the virtue of which, it rotates the plane polarised light (produced by passing ordinary light through Nicol prism) when it is passed through their solutions and the compounds are known as optically active compounds. The optical activity of the substance is a measure of the ability of the substance to rotate the polarisation plane if the solution of the substance is placed in the path of plane-polarised light. For this work, the polarimeter of Perkin-Elmer Model 141 with a Sodium lamp of 584 nm wavelength (D-line) and fitted with a digital counter was used to calculate the amount of degrees of rotation of the plane-polarised light at room temperature by 8.3 percent concentration of each L-, D-and DL-alanine solution. Initially, the French scientist Jean-Baptiste Biot detected optical phenomena. He concluded that the change in direction of the plane-polarised light, when moving through such objects, was simply a rotation of light and had a molecular origin. His dissertation was influenced by an observation by Louis Pasteur. Pasteur observed the presence of two crystals which were mirror images of tartaric acid, an acid present in wine. Through meticulous experimentation, he discovered that one group of molecules rotated the clockwise polarised light while the other group rotated the clockwise light to the same degree. He also observed that a mixture of both, a racemic mixture (or a racemic modification), did not rotate light because the optical activity of one molecule cancelled out the effects of the other molecule. Pasteur was the first to explain the presence of chiral molecules. The optical activity is of two types: Dextrorotatory or the d-form Dextrorotatory in Greek means right rotating, if the compound rotates the plane polarised light to the right, i.e., clockwise direction, it is called dextrorotatory or the d-form and is indicated by placing a positive (+) sign before the degree of rotation. Laevorotatory or the l-form Laevorotatory in Greek means left rotating if the compound rotates the plane polarised light to the left, i.e., anticlockwise direction, it is called laevorotatory or the l-form and a negative (–) sign are placed before the degree of rotation. The angle by which the plane polarised light is rotated is measured by an instrument called polarimeter. Such (+) and (–) isomers of a compound are called optical isomers and the phenomenon is termed as optical isomerism. What is Racemisation and racemic mixture? Racemisation is a process in which optically active compounds (consisting of a single enantiomer) are converted into an equal mixture of enantiomers with zero optical activity (a racemic mix). The rate of racemisation depends on the molecule and conditions such as pH and temperature. How do you separate a racemic mixture? By reacting them with an optically active reagent, you can separate the constituents of a racemic mixture. The product is a diastereomer. Diastereomers possess various physical properties. Use ordinary isolation methods like fractional crystallization you can isolate them. Is Achiral optically active? Rotation direction and magnitude depend on the nature of the electron cloud, so it is reasonable that two identical molecules with identical electron clouds rotate light exactly the same way. Accordingly, achiral molecules do not show optical activity. What is the difference between optically active and inactive? If the light moves to the right, it is called to show optical activity of the dextrorotatory type and if it moves to the left, it is said to show optical activity of the laevorotatory type. And if the light band goes across the lens of Nicol, unnoticed. Optically it is assumed to be inactive. How is a racemate formed? Racemic mixtures are often formed by converting achiral substances into chiral ones. This is because chirality can only be discerned in a chiral environment. In an achiral environment, an achiral substance has no preference for forming one enantiomer over another. What is optical isomerism with example? Isomers are molecules of the same chemical composition but with a different configuration of atoms in vacuum. Unless the structure in space makes the two isomers non-superimposable mirror images of each other, we call them optical isomers or enantiomers. An example of this is the amino acid alanine. What molecules have optical activity? Once techniques have been developed to determine the three-dimensional structure of a molecule, the source of the optical activity of the substance has been identified: compounds that are optically active contain molecules that are chiral. Chirality is the property of a molecule that is the result of its structure. |
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