Optical rotation or optical activity is the rotation of linearly polarized light as it travels through certain materials. In Electrodynamics, linear polarization or plane polarization of Electromagnetic radiation is a confinement of the Electric field vector or Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 It occurs in solutions of chiral molecules such as sucrose (sugar), solids with rotated crystal planes such as quartz, and spin-polarized gases of atoms or molecules. The term chiral (pronounced /ˈkaɪɹ(əl̩/ is used to describe an object that is non- superimposable on its mirror image Solubility of Pure SucroseTemperature(Cg In Materials science, a crystal is a Solid in which the constituent Atoms Molecules or Ions are packed in a regularly ordered repeating Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in Spin polarization is the degree to which the spin, ie the intrinsic Angular momentum of elementary particles is aligned with a given direction It is used in the sugar industry to measure syrup concentration, in optics to manipulate polarization, in chemistry to characterize substances in solution, and is being developed as a method to measure blood sugar concentration in diabetic people. Sugar is a class of edible Crystalline substances mainly Sucrose, Lactose, and Fructose. Polarization ( ''Brit'' polarisation) is a property of Waves that describes the orientation of their oscillations Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties Blood sugar, used in a physiological context is a misnomer and misleading Diabetes mellitus (ˌdaɪəˈbiːtiːz or /ˌdaɪəˈbiːtəs/ /məˈlaɪtəs/ or /ˈmɛlətəs/ often referred to simply as diabetes ( Ancient Greek: grc

History

The two asymmetric crystals forms, dextro and levorotatory, of tartaric acid. Tartaric acid is a white crystalline Organic acid. It occurs naturally in many plants particularly Grapes Bananas and Tamarinds and is

The rotation of the orientation of linearly polarized light was first observed in 1811 in quartz by French physicist François Jean Dominique Arago. Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in François Jean Dominique Arago ( Francesc Joan Dominic Aragó; 26 February 1786 2 October 1853 was a French Catalan Mathematician, Around this same time, Jean Baptiste Biot also observed the effect in liquids and gases of organic substances such as turpentine. Jean-Baptiste Biot (21 April 1774 Paris &ndash 3 February 1862 Paris) was a French Physicist, Astronomer and Mathematician Turpentine (also called spirit of turpentine oil of turpentine wood turpentine gum turpentine is a fluid obtained by the Distillation of Resin obtained from trees In 1822, the English astronomer Sir Joun F. W. Herschel discovered that different crystal forms of quartz rotated the linear polarization in different directions. Simple polarimeters have been used since this time to measure the concentrations of simple sugars, such as glucose, in solution. Polarimetry is the measurement and interpretation of the Polarization of Transverse waves, most notably electromagnetic waves such as radio waves and Light Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology. In fact, one name for glucose, dextrose, refers to the fact that it causes linearly polarized light to rotate to the right or dexter side. Similarly, levulose, more commonly known as fructose, causes the plane of polarization to rotate to the left. Fructose (also levulose or laevulose) is a simple reducing Sugar ( Monosaccharide) found in many foods and is one of the three Fructose is even more strongly levorotatory than glucose is dextrorotatory. Invert sugar, formed by adding fructose to a solution of glucose, gets its name from the fact that the conversion causes the direction of rotation to "invert" from right to left.

In 1849, Louis Pasteur resolved a problem concerning the nature of tartaric acid. Louis Pasteur (27 December 1822 – 28 September 1895 a French Chemist and Microbiologist, is best known for remarkable breakthroughs in the causes and Tartaric acid is a white crystalline Organic acid. It occurs naturally in many plants particularly Grapes Bananas and Tamarinds and is A solution of this compound derived from living things (specifically, wine lees) rotated the plane of polarization of light passing through it, but tartaric acid derived by chemical synthesis had no such effect, even though its reactions were identical and its elemental composition was the same. Lees refers to deposits of dead Yeast or residual yeast and other particles that precipitate or are carried by the action of " Fining " to the bottom of Polarization ( ''Brit'' polarisation) is a property of Waves that describes the orientation of their oscillations In Chemistry, chemical synthesis is purposeful execution of Chemical reactions in order to get a product, or several products Pasteur noticed that the crystals came in two asymmetric forms that were mirror images of one another. Sorting the crystals by hand gave two forms of the compound: solutions of one form rotated polarized light clockwise, while the other form rotated light counterclockwise. An equal mix of the two had no polarizing effect on light. Pasteur deduced the molecule in question was asymmetric and could exist in two different forms that resemble one another as would left- and right-hand gloves, and that the organic form of the compound consisted purely of the one type.

In 1874, Jacobus Henricus van 't Hoff and Joseph Achille Le Bel independently proposed that the phenomenon of optical activity could be explained by assuming that the chemical bonds between carbon atoms and their neighbors were directed towards the corners of a regular tetrahedron. Jacobus Henricus van 't Hoff ( August 30, 1852 &ndash March 1, 1911) was a Dutch physical and organic chemist Joseph Achille Le Bel (1847–1930 was a French Chemist, who was best known for his work in Stereochemistry. This led to a better understanding of the three-dimensional nature of molecules.

Theory

Optical activity is a type of birefringence. Birefringence, or double refraction, is the decomposition of a ray of Light into two rays (the ordinary ray and the extraordinary ray Any linear polarization of light can be written as an equal combination of right-hand (RHC) and left-hand circularly (LHC) polarized light:

where is the electric field of the light. In Physics, the space surrounding an Electric charge or in the presence of a time-varying Magnetic field has a property called an electric field (that can The relative phase between the two circular polarizations, 2θ₀, sets the direction of the linear polarization to θ₀. In Electrodynamics, circular polarization (also circular polarisation) of Electromagnetic radiation is a Polarization such that the tip of the In an optically active material the two circular polarizations experience different refractive indices. The refractive index (or index of Refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves is reduced inside the medium The difference in the indices quantifies the strength of the optical activity,

.

This difference is a characteristic of the material (for substances in solution it is given as the specific rotation). The specific rotation of a Chemical compound is defined as the observed angle of Optical rotation α when plane-polarized light is passed through a sample with a After traveling through length L of material the two polarizations pick up a relative phase of

,

where λ is the wavelength of the light (in vacuum). Consequently, the final polarization is rotated to angle θ₀ + Δθ.

Generally, the refractive index depends on the wavelength (see dispersion). The variation in rotation with the wavelength of the light is called optical rotatory dispersion (ORD). Optical rotatory dispersion is the variation in the Optical rotation of a substance with a change in the Wavelength of Light. ORD spectra and circular dichroism spectra are related through the Kramers–Kronig relations. Circular dichroism (CD is a form of Spectroscopy based on the differential absorption of left- and right-handed circularly polarized Light. The Kramers–Kronig relations are mathematical properties connecting the real and imaginary parts of any complex function which is analytic Complete knowledge of one spectrum allows the calculation of the other.

In summary, the degree of rotation depends on the color of the light (the yellow sodium D line near 589 nm wavelength is commonly used for measurements), the path length L and the properties of the material (e. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. g. Δn or specific rotation and concentration). The specific rotation of a Chemical compound is defined as the observed angle of Optical rotation α when plane-polarized light is passed through a sample with a

Areas of use

Sucrose solution concentration measuring experiment, demonstrating optical rotation.

For a pure substance in solution, if the color and path length are fixed and the specific rotation is known, the observed rotation can be used to calculate the concentration. This usage makes a polarimeter a tool of great importance to those who trade in or use sugar syrups in bulk.

In the presence of magnetic fields all molecules have optical activity. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges A magnetic field aligned in the direction of light propagating through a material will cause the rotation of the plane of linear polarization. This Faraday effect is one of the first discoveries of the relationship between light and electromagnetic effects. In Physics, the Faraday effect or Faraday rotation is a Magneto-optical phenomenon or an interaction between Light and a Magnetic

Optical activity or rotation should not be confused with circularly polarized light. Circularly polarized light is often presented as a linear polarization rotating as the light propagates. However, in this picture the polarization completely rotates in a length equal to the wavelength (roughly one micrometre) and it can happen in vacuum. In contrast, optical activity only occurs in a material and a complete rotation occurs in a length of millimeters to meters, depending on the material.

References

• Eugene Hecht, Optics, 3rd Ed. , Addison-Wesley, 1998, ISBN 0-201-30425-2

See also

• Circular dichroism
• Birefringence
• Polarization