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Halogenderivatives of the hydrocarbons.

LECTURE № 4. Halogenderivatives of the hydrocarbons. I somery of the organic compounds . Spatial construction of the molecules. associate. prof. Ye. B. Dmukhalska, assistant. I.I. Medvid. Outline The nomenclature of halogenderivatives of hydrocarbons.

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Halogenderivatives of the hydrocarbons.

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  1. LECTURE № 4 Halogenderivatives of the hydrocarbons. Isomeryofthe organiccompounds. Spatial construction of the molecules. associate. prof. Ye. B. Dmukhalska, assistant. I.I. Medvid

  2. Outline The nomenclature of halogenderivatives of hydrocarbons. The isomery of halogenderivatives of hydrocarbons. The medico-biological importance of halogenderivatives of hydrocarbons. Physical properties of halogenderivatives of hydrocarbons. The methods of extraction of halogenoalkanes. Chemical properties of halogenoalkanes. Structural isomery of organic compounds. Spatial isomery of organic compounds.

  3. The nomenclature of halogenderivatives of hydrocarbons Halogenderivatives of hydrocarbons are the products of substitution one or several atoms of hydrogen to atoms of halogens in the hydrocarbon molecules. The names of halogenderivatives of hydrocarbons are the names of the same hydrocarbons with added prefix which means the halogen radical. i.e.

  4. If there are several halogen radicals in the molecule of halogenderivatives of hydrocarbons, then all substutients are called in alphabetical order. Some halogenderivatives of hydrocarbons have trivial names:

  5. The isomery of halogenderivatives of hydrocarbons Halogenderivatives of hydrocarbons are characterized by structural, geometrical and optical isomery. Structural isomery is formed by different structure of carbon chain and different location of halogen atoms in the molecule of organic compound.

  6. Geometrical isomery is possible for molecules of halogenderivatives which contain the carbon atoms connected with different substutients. Optical isomery is possible for molecules of halogenderivatives which contain asymmetric carbon atom.

  7. The tables below show some physical data for a selection of haloalkanes.

  8. The methods of preparation of halogenoalkanes 1. Halogenation of the saturated hydrocarbons (SR). 2. The Finkelshtain reaction. R–Cl + NaI→ R–I + NaCl 3. Hydrohalogenation is the joining HCl, HBr or HJ to ethylene and acethylene hydrocarbons. 4. The substitution of the functional groups (for example, –ОН) to atom of any halogen by the action of the following reagents: • HCl, HBr, HI or mixture NaCl + H2SO4(concentrated), KBr + H2SO4(concentrated); b) PCl3, PCl5, PBr3, PBr5or mixture P + I2; c) SOCl2, SO2Cl2.

  9. Chemical properties of halogenoalkanes 1.Halogenalkanes react with water C2H5Br + H2O ↔ C2H5OH + HBr 2. Halogenalkanes react with NaOH or KOH C2H5Br + NaOH ↔ C2H5OH + NaBr 3. Williamson reaction C2H5Br + NaOC2O5 → C2H5−O−C2H5 + NaBr 4. Reaction with salts of carboxylic acids

  10. 5. Reaction with ammonium C2H5Br + NH3 → [C2H5NH3]+Br− C2H5NH2 6. Halogenalkanes react with NaCN or KCN For example, using 1-bromopropane as a typical primary halogenoalkane: You could write the full equation rather than the ionic one, but it slightly obscures what's going on: The bromine (or other halogen) in the halogenoalkane is simply replaced by a -CN group - hence a substitution reaction. In this example, ethanenitrile is formed. C2H5Br + NaCN → C2H5−C≡N + NaBr 7. Reaction with salts of HNO2 C2H5Br + NaNO2 → C2H5NO2 + NaBr

  11. 8. Finkelshtain reaction (catalyst is acetone): C2H5Cl + NaI → C2H5I + NaCl 9. Reaction with NaSN (thioalkohols form) or Na2S (thioethers form): C2H5I + NaSN → C2H5SN + NaI 2C2H5I + Na2S → C2H5−S−C2H5 + 2NaI 10. Reaction with metals: C2H5I + Mg → C2H5MgI 11. Reduction (the reaction runs in the presence of catalysts): C2H5Cl + H2 → C2H6 + HCl

  12. hydrocarbons C H - C N R Nitrocompounds 2 +NaNO C H R nitriles 2 3 C H - N O R 2 2 -NaCl +NaCN n Cl ; h -HCl 2 [H] +NH 3 amines C H - N H R C H - C l R 2 2 +NaSH, H O 2 2 -HCl halogenderivatives -NaCl +NaOH, H O hydrocarbons 2 -NaCl C H - S H R 2 tioalcohols (mercaptans)

  13. hydrocarbons C H - C N R nitrocompounds 2 +NaNO2 C H R nitriles 3 C H - N O R 2 2 2 -NaCl +NaCN n Cl ; h -HCl 2 [H +NH 3 amines C H - N H R C H - C l R 2 2 +NaSH, H O 2 2 -HCl HNO halogenderivatives 2 -NaCl +NaOH, H O hydrocarbons 2 C H - O H R 2 -NaCl alcohols C H - S H R / +R O N a 2 [O tioalcohols / + R -Br O +R Br 1 / R -O-CH -R / +R -C O 2 C H - S - R O N a R R -C ethers 2 1 aldehydes H tioeters (sulphides) O / R -C [O O - R + NaOH + R-OH esters alcoholic solution O -H O R -C 2 O H  carboxylic R-CH=CH 2 acids alkens

  14. O O + NaOH R -CH -C 2 R –CH2-C O N a O H + NaOH alloying +2H O 2 hydrocarbons C H - C N R nitrocompounds 2 +NaNO C H R nitriles 2 3 C H - N O R 2 2 -NaCl +NaCN n Cl ; h -HCl 2 [H] +NH 3 amines C H - N H R C H - C l R 2 2 +NaSH, H O 2 2 -HCl HNO halogenderivatives 2 -NaCl +NaOH, H O hydrocarbons 2 C H - O H R 2 -NaCl alcohols C H - S H R / +R O N a 2 [O] tioalcohols / + R -Br O +R Br 1 / R -O-CH -R / +R -C O 2 C H - S - R O N a R R -C ethers 2 1 aldehydes H tioeters (sulphides) O / R -C [O] O - R + NaOH + R-OH esters alcoholic solution O -H O R -C 2 O H  carboxylic R-CH=CH 2 acids alkens

  15. 7. Isomery of organic compounds Isomery is the phenomenon of existence of compounds which are similar by qualitative and quantitive structures but are different by locations of bonds in molecule. Different compounds that have the same molecular formula are called isomers. If they are different because their atoms are connected in a different order, they are called constitutional isomers. They can have different properties. Formamide (left) and formaldoxime (right) are constitutional isomers; both have the same molecular formula (CH3NO), but the atoms are connected in a different order.

  16. Isomery of Carbon chain is formed by different sequence of atoms in the molecule of the organic compound. C4H10

  17. For cyclic compounds the isomery can change the Carbon cycle in the molecule of the isomer. C6H12

  18. Isomery of the location of the functional group is formed by different locations of identical functional groups and double or triple bonds. C3H7Cl

  19. C6H10Cl2

  20. C4H8

  21. Isomery of the functional group is formed by different functional groups in the molecules. C2H6O

  22. Conformation is the different spatial localization of atoms or atom groups in the molecule as a result of its rotation around -bonds. Hydrogen peroxide is formed in the cells of plants and animals but is toxic to them. Consequently, living systems have developed mechanisms to rid themselves of hydrogen peroxide, usually by enzyme-catalyzed reduction to water. An understanding of how reactions take place, be they reactions in living systems or reactions in test-tubes, begins with a thorough knowledge of the structure of the reactants, products, and catalysts.

  23. Even a simple molecule such as hydrogen peroxide may be structurally more complicated than you think. Suppose we wanted to write the structural formula for H202 in enough detail to show the positions of the atoms relative to one another. We could write two different planar geometries A and B that differ by a 180 rotation about the O—O bond. We could also write an infinite number of nonplanar structures, of which C is but one example, that differ from one another by tiny increments of rotation about the O—O bond.

  24. Structures A, B, and C represent different conformations of hydrogen peroxide. Conformations are different spatial arrangements of a molecule that are generated by rotation about single bonds. Although we can't tell from simply looking at these structures, we now know from experimental studies that C is the most stable conformation.

  25. There is also the conformation in the structure of molecules of organic compounds (alkanes and cycloalkanes). Ethane is the simplest hydrocarbon that can have distinct conformations. Two, the staggered conformation and the eclipsed conformation, deserve special mention and are illustrated with molecular models below.

  26. In the staggered conformation, each C—H bond of one carbon bisects an H—C—H angle of the other carbon. In the eclipsed conformation, each C—H bond of one carbon is aligned with a C—H bond of the other carbon. The staggered and eclipsed conformations interconvert by rotation around the C—C bond, and do so very rapidly. Among the various ways in which the staggered and eclipsed forms are portrayed, wedge-and-dash, sawhorse, and Newman projection drawings are especially useful.

  27. Here it is illustrated the structural feature that is the spatial relationship between atoms on adjacent carbons. Each H—C—C—H unit in ethane is characterized by a torsion angle or dihedral angle, which is the angle between the H—C—C plane and the C—C—H plane. The torsion angle is easily seen in a Newman projection of ethane as the angle between C—H bonds of adjacent carbons.

  28. Eclipsed bonds are characterized by a torsion angle of 0. When the torsion angle is approximately 60, it means that the spatial relationship is gauche; and when it is 180 it is called anti. Staggered conformations have only gauche or anti relationships between bonds on adjacent atoms.

  29. In organic chemistry, chirality most often occurs in molecules that contain a carbon that is attached to four different groups. An example is bromochlorofluoromethane (BrClFCH).

  30. As shown in figure, the two mirror images of bromochlorofluoromethane cannot be superimposed on each other. Because the two mirror images of bromochlorofiuoromethane are not superimposable, BrClFCH is chiral.

  31. A molecule of chlorodifluoromethane (ClF2CH), in which two of the atoms attached to carbon are not chiral. Figure shows two molecular models of ClF2CH drawn so as to be mirror images. As is evident from these drawings, it is a simple matter to merge the two models so that all the atoms match. Because mirror-image representations of chlorodifluoromethane are superimposable on each other, ClF2CH is achiral.

  32. Molecules of the general type are chiral when w, x, y, and z are different. In 1996, the IUPAC recommended that a tetrahedral carbon atom that bears four different atoms or groups be called a chirality center, which is the term that we will use. Several earlier terms, including “asymmetric center”, “asymmetric carbon”, “chiral center”, “stereogenic center” and “stereocenter”, are still widely used.

  33. Noting the presence of one (but not more than one) chirality center is a simple, rapid way to determine if a molecule is chiral. For example, the second atom of carbon C-2 is a chirality center in 2-butanol; it bears a hydrogen atom and methyl, ethyl, and hydroxyl groups as its four different substituents. By way of contrast, none of the carbon atoms bear four different groups in the achiral alcohol 2-propanol.

  34. A molecule may have one or more chirality centers. When a molecule contains two chirality centers, as does 2,3-dihydroxybutanoic acid, there are possible several stereoisomers.

  35. Organic chemists use an informal nomenclature system based on Fischer projections to distinguish between diastereomers. When the carbon chain is vertical and like substituents are on the same side of the Fischer projection, the molecule is described as the erythro diastereomer. When like substituents are on opposite sides of the Fischer projection, the molecule is described as the threo diastereomer. Thus, as seen in the Fischer projections of the stereoisomeric 2,3-dihydroxybutanoic acids, compounds I and II are erythro stereoisomers and III and IV are threo.

  36. Because diastereomers are not mirror images of each other, they can have quite different physical and chemical properties. For example, the (2R,3R) stereoisomer of 3-amino-2-butanol is a liquid, but the (2R,3S) diastereomer is a crystalline solid.

  37. The experimental facts that led van't Hoff and Le Bel to propose that molecules having the same constitution could differ in the arrangement of their atoms in space concerned the physical property of optical activity. Optical activity is the ability of a chiral substance to rotate the plane of plane-polarized light and is measured using an instrument called a polarimeter.

  38. Conversely, when one enantiomer is present in excess, a net rotation of the plane of polarization is observed. At the limit, where all the molecules are of the same handedness, we say the substance is optically pure. Optical purity, or percent enantiomeric excess, is defined as:

  39. Rotation of the plane of polarized light in the clockwise sense is taken as positive (+), and rotation in the counterclockwise sense is taken as a negative (-) rotation. Older terms for positive and negative rotations were dextrorotatory and levorotatory, from the Latin prefixes dextro- ("to the right") and levo- ("to the left"), respectively.

  40. The observed rotation  of an optically pure substance depends on how many molecules the light beam encounters. A filled polarimeter tube twice the length of another produces twice the observed rotation, as does a solution twice as concentrated. To account for the effects of path length and concentration, chemists have defined the term specific rotation, given the symbol []. Specific rotation is calculated from the observed rotation according to the expression where c - the concentration of the sample in grams per 100 mL of solution, and l- the length of the polarimeter tube in decimeters.

  41. It is convenient to distinguish between enantiomers by prefixing the sign of rotation to the name of the substance. For example, optically pure (+)-2-butanol has a specific rotation []27D of +13.5; optically pure (-)-2-butanol has an exactly opposite specific rotation []27D of –13.5.Cahn, Ingold, and Prelog first developed their ranking system to deal with the problem of the absolute configuration at a chirality center, and this is the system's major application. The Cahn-Ingold-Prelog system is called the sequence rules; it is used to specify the absolute configuration at the chirality center in (+)-2-butanol.

  42. (+)-2-butanol has the S configuration. Its mirror image is (-)-2-butanol, which has the R configuration. Often, the R or S configuration and the sign of rotation are incorporated into the name of the compound, as in (R)-(-)-2-butanol and (S)-(+)-2-butanol.

  43. Rules of determination of absolute configuration of (+)-2-butanol 1. Identify the substituents at the chirality center, and rank them in order of decreasing precedence according to the Cahn-Ingold-Prelog priority rules following below.

  44. Precedence is determined by atomic number, working outward from the point of attachment at the chirality center. 2. Orient the molecule so that the lowest ranked substituent points away from you. 3. Draw the three highest ranked substituents as they appear to you when the molecule is oriented so that the lowest ranked group points away from you. 4. If the order of decreasing precedence of the three highest ranked substituents appears in a clockwise sense, the absolute configuration is R (Latin rectus, "right," "correct"). If the order of decreasing precedence is counterclockwise, the absolute configuration is S (Latin sinister, "left"). In order of decreasing precedence, the four substituents attached to the chirality center of 2-butanol are

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