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Investigate molecules with light ICCE – ECRICE 2012, July 15-20, R2012, Rome The molecule, from moles, which means "mole", "small amount", is a collection of at least two atoms (the same element or several elements) are joined by a covalent chemical bond, i.e. when they are bound together by sharing one or more pairs of electrons. The molecules are the fundamental constituents of most of the organic matter present in the universe, as well as the oceans and the atmosphere. THEIR SHAPE The shape of molecules, i.e. how they are distributed in the different components, is a feature that affects not only the physical properties and chemical ones. This is even more apparent when we consider the organic molecules and their activities. Many molecules, although composed from the same atom and combination, described with the same formula, acquire different characteristics when atoms are distributed in space in different ways. It says that two or more molecules have the same formula when they have the same number and type of atoms that make up. In particular, two atoms are "of the same type" if they belong to the same chemical element (i.e. If they have the same atomic number). THEIR POLARITY Any molecule that contains two different generic but atoms bound together chemically, enjoys the polar property. This peculiarity, depending on their different ability to attract electrons, is because of the different location between the Centre of gravity of positive charges (protons) and negative (electrons) that generates an electric dipole (system consisting of two equal and opposite electric charges to sign and separated by a constant distance over time). This property originates from: • • the polarity of the covalent bonds that form the molecule, which in turn depends on the difference in electronegativity of the atoms involved in the bond. The larger the difference in electronegativity, the greater the polarity the symmetry in molecule form that depends on the mutual arrangement of its individual components The polarity of the molecule influence, in turn, other properties: • • • • • chemical reactivity with other molecules bond strength and cohesion solidification temperature and boiling point miscibility and solubility in the presence of solutions electrical conductivity, as well as substances that solutions THE ISOMER It's that phenomenon for which substances which, while having the same formula (share molecular weight percentage composition of atoms) have different physical properties and very often even different chemical behavior. Therefore, the compounds that have the characteristics described above are called isomers and are as below, labeled: • Constitutional isomers (or structural): they have identical formula brute but different connectivity, which are compounds with the same molecular formula but different structural formula. They, therefore, different physical and chemical properties, due to the difference of the bonds between the elements that make up the molecule. In turn are divided into: Constitutional isomers of chain: their distinctive factor is the structure of the "skeleton", the carbonaceous presence and position of branches or rings; they have different physical properties, Chemical reactivity but pretty similar Constitutional isomers of position: the element that characterizes them is the location of multiple ties or groups containing atoms other than carbon and hydrogen; they, belonging to the same class of compounds, despite different physical properties, their chemical reactivity similar Constitutional isomers of functional group: despite having the same formula, have different functional groups and, consequently, their chemical and physical properties very different • Stereoisomers: they have the same formula, same connectivity, but they are not stackable owing to different three-dimensional orientation of atoms in space. They are distinguished: Diastereo-Isomers: there are two isomers in which one is not the mirror image of the other. Among diastereo-isomers: Geometric isomers (cis-trans): only present in molecules in which two carbon atoms linked by a double bond are both linked in turn to two different groups; more generally, they occur in molecules whose structure prevents free rotation around one or more links. The physical properties of these isomers are different, while their chemical reactivity is generally similar. It's worth remembering that there are notable exceptions due to the particular geometrical configurations Isomers conformers (or conformational): while no one stereo center (carbon atom become tethered to four Chiral because atoms or four different groups of atoms) are stereoisomers that are achieved when the atoms revolve around single bonds, giving rise to different conformations of the molecule. They have the same formula, same connectivity but are not stackable Rotameri isomers: are conformers that differ by the twisting of one (and only one) link. It is important to bear in mind that the vision must be "front", i.e. observed frontally the axis of the Isomers enantiomers: they are molecules that exhibit stereo genic element i.e. atoms because of whom admit two isomers molecules that have a mirrored form of the other non-stackable ISOM COSTITUZIONAL of FUNCTIONAL GROUP of CHAIN of POSITION ERS STEREOISOMERS DIASTEREO-ISOMERS GEOMETRIC ISOMERS ENANTIOMERS CONFORMERS ROTAMERI THE CHIRALITY It is the property of any hard object (or a spatial arrangement of points and atoms) to have a mirror image in three dimensions is not stackable. An object with this property is called chiral. THE ENANTIOMORPHISM It is the geometric transform that converts an object into its mirror image. As a result, you say enantiomorphic a pair of molecular entities that are mirror images of each other and not overlap; in the case of molecules, enantiomers instead of enantiomorphic. THE OPTICAL ACTIVITY AND THE OPTICAL ROTATION It is the property of rotate the plane of polarized light vibration possessed by Chiral chemicals and then optically active. The optical power is the measure of optical activity. With the general term wave is a disturbance that comes from a source and propagates in time and space, delivering energy without result associated with movement of the subject. Waves can propagate through a material or, more simply, in a vacuum. THEIR CHARACTERISTICS A wave can be characterized by a single oscillation or a sequence (or train) with wave-like features. In general, the waves are formed by: • • • crest belly wave fronts of propagation: present only in trains of waves and can be categorized into transverse or longitudinal THE REFERENCE PARAMETERS The waves differ from one another in order to: • • • • • • • amplitude wavelength period frequency phase speed of propagation energy and power associated with the speed of propagation THE MEANS OF PROPAGATION The medium in which the waves travel can be classified into: • • • limited or unlimited homogeneous isotropic or anisotropic THE EFFECTS Each wave takes a common behaviour in standard situations and may undergo the following phenomena: • • • • • • • amplitude attenuation during propagation of the medium meditation refraction diffraction dispersion interference Doppler effect WAVELENGTH TYPES Based on different characteristics of waves, they can be classified into categories concerning: the type of medium: • • • mechanical waves (sound waves) non-mechanical waves (light waves) the size of the medium in which they propagate: • • • linear or one-dimensional waves (swing by a rope) two-dimensional waves (circular waves on a water surface) three-dimensional waves (sound waves) their direction of propagation vector: • • • • • longitudinal waves (pressure waves) transverse waves (electromagnetic waves) propagation: plane waves (waves on the water surface) spherical waves (pressure waves) cylindrical waves (adjacent waves an antenna) the medium in which it propagates and physical characteristic that it represents: • • elastic waves or displacement electromagnetic radiation (light, radio waves, ultraviolet rays, x-ray) THE SINUSOIDAL WAVES They are a particular solution of the general equation of waves: v= V = wave frequency T = wave periodicity 𝟏 𝑻 In fact, if we consider a one-dimensional wave, in describing it, you consider the horizontal position x of the impulse and time T that we observe the wave itself: the amplitude of the oscillation y of the particles around the equilibrium position is in terms of these elements: y= f(x,T) y = swing x = the time dimension T = time The viewpoints are two: • choosing to evaluate the temporal dimension (x fixed), we will state the y swinging time dependence t: y= f(T) • choosing instead to focus on a medium perturbed at a certain moment (T set) ot-hold sway y expressed as a function of position x: y= f(x) THE ELECTROMAGNETIC WAVES An electromagnetic wave is a disturbance of electric and magnetic nature simultaneously that propagates through space and that can carry energy from one point to another. This disruption is the simultaneous vibration of two intangible entities called the electric field and magnetic field around their equilibrium position (which corresponds to no disruption). An electromagnetic wave travels in the direction perpendicular to the direction of oscillation of the fields, it is, therefore, of a transverse wave. Electromagnetic waves propagation characteristics in the media or in presence of obstacles depends on the frequency (and therefore wavelength). WHAT HAPPENS IN AN ELECTROMAGNETIC WAVE An electron building generates, because of his position, an electric force in the surrounding space, the electric field, which decreases as the inverse square of the distance. By swinging a first electron, the electric field is perturbed at the points around due to the change from the electron during its swing. A variation of the electric field get black-a magnetic field. These swings of the electric field — and therefore also of the magnetic field — propagate by electron generating electromagnetic waves. A second electron is stationary at a certain distance from the first, begins to wobble soon invested by electromagnetic wave produced by the electron. Even the electric field of the second electron, then, will be disrupted by its oscillations and throws itself a magnetic field, allowing the wave propagation. The sizes of the wave, i.e. its breadth, give a measure of the intensity of the electric wave. The radiation of an electromagnetic wave is composed of electromagnetic waves, which consist in swing concert-nanny of an electric field and a magnetic field. These on-de propagate in the direction orthogonal to that of oscillation. Finally, an electromagnetic wave is emitted whenever a charged particle undergoes acceleration due to some force. THEIR CLASSIFICATION It is customary to classify the different magnetic waves: • • • • • • • • radiofrequency waves microwave infrared spectrum visible spectrum light, produced by quantum transitions of atoms or molecules. Depending on the wavelength, it affects the retina ultraviolet rays (Sun) x-rays gamma rays THE LINEARLY POLARIZED LIGHT Linearly polarized light (or polarized on a plane) is the energy that results from ordinary light passing through an optical polarizer filter, where the emerging light is a beam whose electric vector vibrates on a single floor. Actually, the plane-polarized light is the resultant of two circularly polarized components direct opposite, rightward and leftward, in concordance with the same phase and frequency and amplitude. When polarized light interacts with a chiral medium, his plan of polarization varies its orientation relative to the direction of propagation: such distortion is known as optical rotation, whereby the optical activity is the ability of a substance, called optically active, to rotate the plane of polarized light. GLOSSARY Belly: lowest point wave Crest: highest point of a wave Cylindrical wave: wave that unfolds spatially so symmetric with respect to an axis Dispersion: Wave Division under waves in dependence of their frequency Doppler effect: frequency shift of a periodic wave traveling relative to the direction of observation both swinging and varying their towards a special flavor and intensity Elastic wave: wave mechanics in which the physical properties of the medium are elastic and that has verified the Hooke's law Electromagnetic radiation: form of energy associated with the electromagnetic interaction and the propagation in the space time of the electromagnetic field in the form of electromagnetic waves Gamma ray: wave with a wavelength range of 1 * 10-10 m and 1 * 10-14 m. Originates from nuclear power and is used in special therapies Gravitational wave: fluctuation of gravitational field Homogeneous medium: physical properties in an anywhere do not vary as a result of translation Infrared spectrum: wave of wavelength ranging from 1 mm to 7.8 * 10-7 m. This is a wave produced by excited molecules and hot bodies; it is used in industry and medicine Interference: vector sum (even nothing) of two waves that come into contact with each other Isotropic medium: physical properties in an anywhere do not change as a result of rotation from that point Limited medium: medium that has a finite extension Longitudinal wave: the vibration agrees with the direction of wave propagation • magnetic field Mechanical wave: wave that propagates only in non-material means empty because they exploit the properties of elasticity of the medium for their propagation Microwave: wave with a wavelength of between 0, 3 m and 1 mm. This category, produced by special electronic products, used in radar systems and those of special media Non-mechanical wave: wave that propagates in non-material means that the vacuum Ocean wave disturbance: surface propagating into the water Optical rotation: rotation, in degrees, of the plane of polarized light caused by the passage of this through a solution of an optically active substance Optically active substance: substance able to rotate the plane of polarized light vibration Ordinary light: light consists of electromagnetic waves that vibrate in all directions perpendicular to the direction in which it travels, i.e., spreads in the form of waves develop on different planes along the line of propagation. Its range consists of two components that vibrate on planes perpendicular to each other Plane wave: steady frequency wave whose wave fronts are infinite parallel planes of constant amplitude normal to the wave vector Radio frequency wave: waves with wavelengths ranging from a few miles up to 0.3 m. This category is used in the transmitting system of radio and television and is generated by special electronic devices Reflection: change of direction of wave propagation due to a clash with a reflective material Refraction: wave direction change caused by the change of the means of propagation (example: different densities) Sound: mechanical wave that propagates through gas (typically air), liquid or solid, whose frequency can be perceived by the auditory apparatus Spherical wave: the wave front is a sphere and, therefore, its source is a point so that the wave front to propagate in proportion to the distance r from the source Translation: affine transformation of Euclidean space which moves all points a fixed distance in the same direction Transverse wave: the vibration is perpendicular to the direction of wave propagation Ultraviolet ray: wave whose wavelength values are between 107 m 3.8 * and 6 * 10-7 m. It is used in some medical applications and application in sterilization processes Visible spectrum: narrow band of audible waves from the retina of the human eye. This is a wave with a wavelength of between 7.8 * 10-7 m and 3.8 * 10-7 m Wave propagation: diffraction (example: when passing through a narrow slit) Wave fronts of propagation: sets of points agreed that vibrate, so that, for each of them, the displacement from the equilibrium position to assume the same value in every moment Wavelength: distance between two crests or between two wombs of his wave form Width: maximum variation of greatness in a periodic oscillation X ray: wave extending from 1nm to 1 * 10-11 m. Produced by electron quantum transitions innermost atomic structures (more strongly bound to the nucleus), is very penetrating The polarimeter is the instrument used to measure the optical rotation of optically active substances. DESCRIPTION 1. light source: LEDs of different colors with wavelengths (λ) different 2. Switch to the choice of led 3. Lens 4. First polarizer 5. Tube with sample 6. Second polarizer for optical rotation measuring 7. Goniometer and nonius 8. Rotating disk manual 9. External protective cylinder complete with base TECHNICAL CHARACTERISTICS Angle measurement accuracy: ± 0.1 mm Tube sample length: 100 cm Weight: 3.25 Kg Dimensions: l 22 cm; h 122 cm; p 22 cm Monochromatic light source: led OPERATING METHOD PREPARATION: • • • • • • • Measuring of white to attach the position of zero Fill the tube with the solvent to analyze Place the sample in the polarimeter tube Place the goniometer on head to the tube Switch on the led of the desired color by selecting it with the switch Rotate the goniometer until the led goes dark Check the position of zero MEASURING THE OPTICAL ACTIVITY: • • • • • • • Prepare the solution to be analyzed Pour the solution inside the measuring tube Insert the sample tube with solution in the polarimeter Place the goniometer on head to the tube Measure the level of the liquid in the tube Switch on the led of the desired color by selecting it with the switch Rotate the goniometer until the led goes dark • • • • Read the value on the goniometer and calculating the angle difference with sample zero Repeat the measurement halving the length of the path (or halve the amount of fluid) into the measuring tube If the new angle corresponds to α/2 or α/2 ± 180°, the substance is called dextrorotatory, instead if you get values equal to α-180°/2 or α-180°/2 ± 180° the substance is called levorotatory Apply the formula of optical rotation to get the concentration of the compound or the specific optical rotation of substance 𝛂=𝐜∙𝐥∙𝐤 α= angle of experiment rotation experiment c= concentration of the compound l= length of path k= specific optical rotation WARNINGS • • • • The instrument must be kept clean and breezy with temperature and humidity within the normal range (about 20° C 50% UHR) After using the measuring pipe must be carefully cleaned with distilled water Do not use abrasive materials to clean the optics of the instrument (including paper) Hold the instrument always covered (when not in use) to prevent the introduction of dust • Do not disassemble the instrument; mistakes in assembling mechanical alignment that can irreparably undermine the accuracy are instrument