Halogenderivatives of the hydrocarbons.

1. Halogenderivatives of the hydrocarbons. Isomeryofthe organiccompounds. Spatial construction of the molecules. Ass. Medvid I.I., ass. Burmas N.I.

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. 1. 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. 2. 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. 3. The medico-biological importance of halogenderivatives of hydrocarbons Because of the atom of halogen is present in the molecule, many halogenderivatives of hydrocarbons are physiologically active. For example: C2H5Cl – ethyl chloride – is the means for the local anaesthetization when there are neuralgia, large superficial cuts, wounds. Because of the fast evaporation from the skin ethyl chloride causes the strong cooling and loss of painful sensitivity; CHCl3 – chloroform – is the means for inhalative narcosis. It is relatively toxic. In the presence of light it can oxidize with forming of HCl and phosgene () – which is very toxic compound; CHJ3 – iodoform – is the antiseptic means. It is crystal compound, it has yellow colour. It is used as powder and ointment; СF3–CHBrCl – fluorotane – (2-bromo-1,1,1-trifluoro-2-chloroethane) – is one of the best means of general narcosis; CCl2=CHCl – trichloroethylene – is the strong narcotic means, especially for short-term narcosis. Because of the presence of halogen atom in the benzene ring the compound is more toxic. Because of the presence of halogen atom in the side carbon chain of the benzene ring the compound is more lachrymatory.

8. 4. Physical properties of halogenderivatives of hydrocarbons Physical state and smell Haloalkanes are colorless, sweet-smelling liquids. The lower members like methyl chloride, methyl bromide and ethyl chloride are colorless gases while members having very high molecular masses are solids. Solubility Haloalkanes are not able to form hydrogen bonds with water and, even though they are polar in nature, they are practically insoluble in water. However, they are soluble in organic solvents like alcohol, ether, benzene, etc. Density Chloroalkanes are lighter than water while bromides and alkyl iodides are heavier. With the increase in the size of the alkyl group, the densities go on decreasing in the order of : fluoride > chloride > bromide > iodide. Boiling points The boiling points of alkyl chlorides, bromides and iodides follow the order RI > RBr > RCl where R is an alkyl group. With the increase in the size of halogen, the magnitude of Van der Waals forces increases and, consequently, the boiling points increase. Also, for the same halogen atom, the boiling points of haloalkanes increase with increase in the size of alkyl groups.

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

10. 5. The methods of extraction of halogenoalkanes 1. Chlorinating and brominating of the saturated hydrocarbons (the reactions of radical substitution (SR). 2. The Finkelshtain reaction. R–Cl + NaJ → R–J + NaCl  3. Hydrohalogenation is the joining HCl, HBr or HJ to ethylene and acethylene hydrocarbons. This reaction runs by Markovnikov rule. 4. The substitution of the functional groups (for example, –ОН) to atom of any halogen by the action of the following reagents: • HCl, HBr, HJ or mixture NaCl + H2SO4(concentrated), KBr + H2SO4(concentrated); b) PCl3, PCl5, PBr3, PBr5or mixture P + J2; c) SOCl2, SO2Cl2.

11. 6. 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

12. 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, butanenitrile is formed. C2H5Br + NaCN → C2H5−C≡N + NaBr 7. Reaction with salts of HNO2 C2H5Br + NaNO2 → C2H5NO2 + NaBr

13. 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

14. 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)

15. hydrocarbons C H - C N R nitrocompounds 2 +NaNO 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

16. O O + NaOH R -CH -C 2 R -CH -C O N a 2 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

17. 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.

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

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

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

22. C6H10Cl2

23. C4H8

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

25. 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.

26. 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.

27. 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.

28. 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.

29. 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.

30. 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.

31. 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.

32. For characteristic of optical isomery the optical activity and chirality are very important. Everything has a mirror image, but not all things are superimposable on their mirror images. Mirror-image superimposability characterizes many objects we use every day. Cups and saucers, forks and spoons, chairs and beds are all identical with their mirror images. Many other objects though — and this is the more interesting case — are not. Your left hand and your right hand, for example, are mirror images of each other but can't be made to coincide point for point, palm to palm, knuckle to knuckle, in three dimensions.

33. In 1894, William Thomson (Lord Kelvin) coined a word for this property. He defined an object as chiral if it is not superimposable on its mirror image. Applying Thomson's term to chemistry, we say that a molecule is chiral if its two mirror-image forms are not superimposable in three dimensions. The word chiral is derived from the Greek word cheir, meaning "hand," and it is entirely appropriate to speak of the "handedness" of molecules. The opposite of chiral is achiral. A molecule that is superimposable on its mirror image is achiral.

34. 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).

35. 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.

38. The mirror images of bromochlorofluoromethane have the same constitution. That is, the atoms are connected in the same order. But they differ in the arrangement of their atoms in space; they are stereoisomers. Stereoisomers that are related as an object and its nonsuperimposable mirror image are classified as enantiomers. The word enantiomer describes a particular relationship between two objects. Just as an object has one, and only one, mirror image, a chiral molecule can have one, and only one, enantiomer.

39. 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.

40. 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.

41. 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.

42. Carbons that are part of a double bond or a triple bond can't be chirality centers.A carbon atom in a ring can be a chirality center if it bears two different substituents and the path traced around the ring from that carbon in one direction is different from that traced in the other. The carbon atom that bears the methyl group in 1,2-epoxypropane, for example, is a chirality center. The sequence of groups is O—CH2 as one proceeds clockwise around the ring from that atom, but is CH2—O in the counter clockwise direction. Similarly, C-4 is a chirality center in limonene.

44. 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.

45. Stereoisomers that are not related as an object and its mirror image are called diastereomers; diastereorners are stereoisomers that are not enantiomers. To convert a molecule with two chirality centers to its enantiomer, the configuration at both centers must be changed. Reversing the configuration at only one chirality center converts it to a diastereomeric structure. Enantiomers must have equal and opposite specific rotations. Diastereomers can have different rotations, with respect to both sign and magnitude.

47. Thus, as figure shows, the (2R,3R) and (2S,3S) enantiomers (I and II) have specific rotations that are equal in magnitude but opposite in sign. The (2R,3S) and (2S,3R) enantiomers (III and IV) likewise have specific rotations that are equal to each other but opposite in sign. The magnitudes of rotation of I and II are different, however, from those of their diastereomers III and IV. In writing Fischer projections of molecules with two chirality centers, the molecule is arranged in an eclipsed conformation for projection onto the page. Horizontal lines in the projection represent bonds coming toward you; vertical bonds point away.

48. 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.

49. 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.

50. 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.