Understanding The Stereochemistry Of Organic Compounds Environmental Sciences Essay

Understanding The Stereochemistry Of Organic Compounds Environmental Sciences EssayStereoisomers argon outlined as molecules of identical atomic compositions (molecular verbalisms), yet with different stick toing line of battles of atoms or druthers of their atoms in space. Based on this definition, several types of isomerism be possible including fundamental, configurational, and conformational isomerism. Constitutional isomers (also called structural or positional isomers) ar molecules with the same atomic composition except different alignmenting arrangements between atoms, as illustrated by theexamples of catechol, resorcinol, and hydroquinone . All of these compounds view as the same atomic composition (C6H6O2), nevertheless different bonding arrangements of atoms and argon therefrom distinct chemical entities with different chemical and animal(prenominal) properties.Stereochemistry (from the the greek stereos,meaning solid) refers to chemistry in three dimension s.Since most molecules are three dimension , stereochemistry ,infact, prevade all chemistry.It is non so much a branch of the subject as a point of view, and wheather one choose to take this point of view in every given situation depends on the problem one wants to solve and on the tools one has available to solve it.We factorize stereochemistry into its ststic and dynamic aspects.STATIC stereochemistry (better called stereochemistry of molecules) deals with the counting of stereoisomer, with their structure, with their energy and with their physical and most of their spectral property.DYNAMIC stereochemistry(stereochemistry of reaction) deals with the stereochemical requirement and stereochemical outcome of chemical reactions, including interconversion of conformational isomerms.If we represent the following imaginary molecule with no stereochemistry, there is nothing apparently peculiar(prenominal) most itHowever, if we represent it fully, including the position of atoms in spa ce, it becomes apparent that the description above is vague, as it encompasses two molecules those down the stairsThis is what stereochemistry is we merchant ship define compounds into many way and shadow also originate many new compouds.So stereochemistry is chemistry that studies the property of isomers.HISTORYHistorically the origins of stereochemistry stem from the discovery of plane polarized spark by the French physicist MALUS.In 1815 biot note that certain natural organic compounds rotate plane polarized lightness asARGO(1811), discovered that a quartz plate, cut at a right angle to its crystal axis ,rotates the plane polarized light through an angle proportional to the thickness of the plate. S ome quartz crystal rotate towards go away while some to the right.However in 1847 LOUIS PASTEUR find that equimolar solution of seprated mixture dedicate equal but opposite optical activity.In 1874 LEBEL and VANT-HOFF proposes that carbon with 4 attachment is tetrahedral and a molecule having a teahedral geometry will exist as pair of two isomer.ISOMERISMIsomers are defined as molecules of identical atomic compositions (molecular formulas), but with different bonding arrangements of atoms or orientation of their atoms in space. Based on this definition, several types of isomerism are possible including constitutional, configurational, and conformational isomerism. Constitutional isomers (also called structural or positional isomers) are molecules with the same atomic composition but different bonding arrangements between atoms, as illustrated by theexamples of catechol, resorcinol, and hydroquinone . All of these compounds perplex the same atomic composition (C6H6O2), but different bonding arrangements of atoms and are thus distinct chemical entities with different chemical and physical properties.GEOMETRIC ISOMERISMGeometric isomers lease the same empirical formula or molecular formula and also the same structural formula, but book a different recoun ting arrangement of the substituent assemblages. For example, the two geometric isomers of 1,2-dichloroethene ( rule 2) have the molecular formula of C2H2Cl2, and the same structural formula of Cl(H)C=C(H)Cl, but the relative position of the two chlorine atoms can either be the same gradient of the C=C double bond (i.e., cis, see send off 2a) or on opposite sides of the C=C double bond (i.e., trans, see Figure 2b). The use of cis and trans is not limited to organic compounds such as olefins, but can also be utilise in metal complexes, e.g., Figure 3.Figure 2 The two geometric isomers of 1,2-dichloroethene. Figure 3 Examples of (a) cis and (b) trans geometric isomers for metal complexes. When it is not possible to reveal geometric isomers by the basis cis or trans, the terms facial (fac, Figure 4a) or meridinal (mer, Figure 4b) are commonly employed. Examples of (a) fac and (b) mer geometric isomers for metal complexes.POLARIMETRY AND OPTICAL ROTATIONPolarized light is obtained by passing ordinary light through a polarizer , such as nicol prism.The orientation of the polarizers axis of polarization determines the plane of the resulting polarized light.OPTICAL ACTIVITY-Unpolarized light from a suitable source is do to pass through a polarizer that usually consists of a pair of crossed Nichol prisms. The light leaving the polarizer is plane polarized and, in the diagram, the angle of the Nichol prisms has been adjusted to produce steeply polarized light. This light is then passed through a tube containing the sample. If the sample is optically active, the plane of the polarized light will be rotated, as shown in figure The outcome of whirling will depend on the polarizability of the substance and its concentration. The light from the sample cell is then passed through an different pair of crossed Nichol prisms called the analyzer. The analyzer prisms are then rotated so that the transmitted light is again vertically polarized. The angle through which th e analyzer has been turned is called the angle of polarization. Clockwise rotation of polarized light is designated as (+) and anti clockwise rotation as ( ). The established method of defining rotation is that the (+) isomer is termed dextro and the ( ) isomer laevo.Optical activities of enantiomerA pair of enantiomer are distinguised by their optical activites because a pair of enantiomers rotates the plane of polarized light by equal amounts in opposite direction.In a mixture of two enantiomers, each contribute to the optical rotation in proportion to its concentration.It follows that a sample containing equal amounts of two enantiomer must have an observed optical rotation of zero.Enantiomer of tartaric acid isENANTIOMEREnantiomers are compounds that have the same ordering of atoms as each other, but that differ from one another when viewed in three dimensions. The compound drawn to the left is an enantiomer because it has the H3C group projecting up from the page toward the re ader. The corresponding enantiomer would have the H3C group projecting below the page away from the reader. A racemic mixture refers to a 5050 mixture of two corresponding enantiomers.CHIRALITYChirality is a structural property of an object. An object is utter to bechiral if its mirror image can not be setd with itself by the means of rotations. The most familiar example of a chiral object is our hand. To see this, we world-class have to convince ourselves that our two hands are mirror images of each other. Then we can spend hours rotating our two hands around and trying to superimpose them point-to-point, only to find out that it is impossible. Thus a human hand is a chiral object. An object is said to be achiral if its mirror image is its exact echoDIASTEREOMERThey are different physical/chemical properties in chiral/achiral environments.Stereoisomers that are not enantiomer are called diastereomers.FISHER PROJECTIONFischer sound projections are used to visually describe vari ous isomers of the same compound in two dimensions. They are also used as a basic test for optical activity (or chirality). The Fischer projection looks like a cross, with the (invisible) asymmetric carbon located at the points where the lines cross. The horizontal lines are taken to be wedges, or bonds that project out of the plane of the paper. The vertical lines are taken to project away form the viewer, or back below the plane of the paper, as dashed lines.CONFIGURATIONConfigurational isomers are defined as molecules of identical atomic composition and bonding arrangements of atoms, but different orientations of atoms in space, and these different orientations cannot interconvert freely by bond rotation. Since these types of isomers differ only in relative spatial orientations of atoms, they are commonly referred to as stereoisomers. Configurational stereoisomers are subcategorized as optical isomers (enantiomers) or geometric isomers (Fig. 2), depending upon the hybridization s tate and geometry of the atoms that impart the properties of stereoisomerism and the boilersuit structure of the molecule. Stereoisomers of this type are distinct chemical entities that may have different chemical and physical properties.CONFORMATIONConformational isomers (conformers) are stereoisomeric forms characterized by different relative spatial arrangements of atoms that result from rotation about sigma bonds. Thus, unlike configurational isomers, conformers are interconverting stereochemical forms of a single compound.STEREOCHEMICAL CORRELATIONThe absolute configuration of most organic compounds are determined instead by using chemical reaction correlate with other compounds of known absolute compounds is known as stereochemical correlation.STEREOCHEMISTRY OF CHEMICAL REACTIONNo chemical reaction can be planned without stereochemical details,and no chemical reaction can be planned without considering problems oe stereochemistry that might arise.A.STEREOCHEMICHEMISTRY OF ADD ITION REACTIONAn sum reaction can occur in either of two stereochemically different ways,called syn addition and anti addition.Stereochemistry of an addition can be determined only when the stereochemically different modes of addition give rise to stereochemically different products.Syn and anti addition gives different products only when both carbons of the double bond becomes carbon stereocentre in the product.STEREOCHEMISTRY OF SUBSITITUTION REACTIONA substitution reaction can occur in two stereochemically different ways, called retention of configuration and inversion of configuration then x and x have the same relative stereochemical position.Substation rxn with retention of configuration isIt implies that if x and x have the same relative priorities in the R,S system then the carbon that undergoes subsititution will have the same configuration in the reactant and the product.When the subsititution occur with inversion of configuration then x and x have different relative ster eochemical positions.Subsititution with inversion of configuration isThey have same relative priorities in the R,S system, then the carbon that undergoes substitution must have opposite configuration in the reactant and the product.Stereochemistry of ReactionsTwo products are formed when a chiral substrate that possesses an asymmetric, electrophilic carbon is applied in an reaction. One of them has the same absolute configuration as the starting product (if, according to the CIP rules, the leaving group and the nucleophile have the same position in the priority order of the substituents), which is called retention. In contrast, the other product possesses the opposite absolute configuration, known as inversion. In reactions, the nucleofuge exits the substrate sooner the nucleophilic attack can ever occur. Thus, an intermediate carbocation is then formed. Due to the carbocations trigonal planar shape, its two enantiotopic sides are susceptible to attack by the nucleophile with the s ame probability.Stereochemistry ofReactionsIf a pure enantiomer is applied to an reaction, three different stereochemical results are conceivableThe initial spatial arrangement of the reaction centers substituents remains (retention).The initial substituents spatial arrangement is inverted (inversion).Retention, as well as inversion takes place. If retention and inversion occur to the same degree, the reaction yields a racemate (racemization).Stereochemistry of E2 EliminationIn the E2 elimination reaction, the carbon-hydrogen sigma bond and the carbon-leaving group sigma bond must lie in the same plane. This allows the orbitals to begin to overlap to form the pi bond as the bonds to the hydrogen and the leaving group are broken. There are two possible planar arrangements of these bonds both on the same side of the C-C bond (syn-coplanar) or on opposite sides of the C-C bond (anti-coplanar)In syn the bond from the carbon to the leaving group (green) and the bond from the other carbon to the hydrogen (blue) are syn-coplanar. The dihedral angle between these bonds is zero degrees. This conformation is eclipsed about the carbon-carbon bondIn anti the bond from the carbon to the leaving group (green) and the bond from the other carbon to the hydrogen (blue) are anti-coplanar. The dihedral angle between these bonds is clxxx degrees. This conformation is staggered about the carbon-carbon bond. Because this conformation is more stable than the eclipsed conformation required for syn elimination, anti elimination is preferred in E2 reactionsSTEREOCHEMISTRY OF ALKANEConformationsAlkane conformers arise from rotation around sp3 hybridised carbon carbon sigma bonds. The smallest alkane with such a chemical bond, ethane, exists as an infinite number of conformations with respect to rotation around the C-C bond. Two of these are recognised as energy minimum (staggered) and energy maximum (eclipsed) forms. The existence of specific conformations is due to hindered rotation a round sigma bonds, although a role for hyperconjugation is proposed by a competing theory.CONSTITUTIONAL ISOMERThere are different types of isomer.Isomers such as butane and isobutane that differ in the connectivity of their atom are termed as constitutional isomer.butane and isobutane are only constitutional isomer with the formulaC4H10 .However ,more constitutional isomer are possibles for alkane with more carbon atoms.STEREOCHEMISTRY OF ALKENEThe stereochemistry of halogen addition is unequivocally determined by the anti addition and the almost completely restricted rotation of the carbon-carbon bond of the halonium ion. Therefore, the bromination of cis-2-butene yields a racemate of (2R,3R)- and (2S,3S)-dibromobutane, whereas the bromination of trans-2-butene yields the meso compound.CIS TRANS GEOMETRY OF ALKENEIf alkenes have two different substituents at each end of the C=C then they can exist as stereoisomers (as geometric isomers ).This is because there is restricted rotati on of the double bond due to the pi bondCIS TRANSE-Z agreementThe cis- / trans- style is based on the longest chain whereas the E/Z style is based on a set of priority rules.You need to know both styles.Z SYSTEM cis-but-2-eneor (Z)-but-2-eneThe E- and Z- style is more reliable and particularly suited to highly substituted alkenes, especially when the substituents are not alkyl groups.STEREOCHEMISTRY-FUTURE PROSPECTUS AND APLLICATION1.Temperature modulation of the stereochemistry of enzymatic catalys.2.It is used in medical purpose for malarial prevention, control and research3.The HeI resonance line used for UPS was produced by DC discharge of pure helium gas.4. Stereochemistry is highly used in biochemistry in various purposes like enzyme catalyst e.t.c.5. Penning ionization is known to be one of the most important types of chemical reaction in aerospace.Steric shielding effect of methyl group an penning ionization in subsitutional aniline.6. Stereochemistry is always used in disc overing new compounds7. Stereochemistry is used to know the property and other new property of the existing compound or the compounds not known..REFRENCESHehre, W.J.(1975),J.AM.CHEMKARLE J.(1973),ELECTRON DIFRACTION IN NACHOD,F.C AND ZUKERMAN, VOL 5 P12.ELIEL L. ERNEST(2009),STEREOCHEMISTRY OF ORGANIC COMPOUNDS,WILEY STUDENT EDITIONLOUDON MARC G.(2009),4th EDITON ,ORGANIC CHEMISTRY ,OXFORD UNIERSITY PRESSWEBSITEhttp//commons.wikimedia.org/wiki/ billExample_of_stereoisomershttp//www.google.co.in/imgres?imgurl=http//img121.imageshack.us/img121/5564/81111276.jpgimgrefurl=http//www.chemicalforums.com/index.WWW.CHEMISTRY.UKwww.wileyindia/chem.com