ass. Medvid I.I., ass. Burmas N.I.

1. Reactionary ability of the saturated hydrocarbons (alkanes, cycloalkanes). Reactionary ability of the unsaturated hydrocarbons (alkenes, alkadienes, alkynes). ass. Medvid I.I., ass. Burmas N.I.

2. Outline Concept of alkanes Structure of alkanes Nomenclature of alkanes The isomery of alkanes The methods of extraction of alkanes Physical properties of alkanes Chemical properties of alkanes Structure of cycloalkanes Nomenclature of cycloalkanes Conformation of cycloalkanes The methods of extraction of cycloalkanes Chemical properties of cycloalkanes

3. Concept of alkenes The nomenclature of alkenes The isomery of alkenes The methods of extraction of alkenes Physical properties of alkenes Chemical properties of alkenes The nomenclature of dienes Configurational isomers of dienes The methods of extraction of dienes Chemical properties of dienes The nomenclature and isomery of alkynes The nomenclature and isomery of alkynes The methods of extraction of alkynes Physical properties Chemical properties

4. 1. Concept of Alkanes Alkanes are the hydrocarbons of aliphatic row. Alkanes are hydrocarbons in which all the bonds are single covalent bonds (-bonds). Alkanes are called saturated hydrocarbons. Alkanes have the general molecular formula CnH2n+2. The simplest one, methane (CH4), is also the most abundant. Large amounts are present in our atmosphere, in the ground, and in the oceans. Methane has been found on Jupiter, Saturn, Uranus, Neptune, and Pluto, and even on Halley's Comet.

5. Methane is the first in the homological row of alkanes following below: Methane CH4 Ethane C2H6 Propane C3H8 Butane C4H10 Pentane C5H12 Hexane C6H14 Heptane C7H16 Octane C8H18 Nonane C9H20 Decane C10H22 Undecane C11H24 Dodecane C12H26 Tridecane C13H28 Tetradecane C14H30 Pentadecane C15H32 Alkanes:

6. 2. Structure of Alkanes Alkanes can have either simple (unbranched) or branched Carbon chain. Alkanes with unbranched Carbon chain are called normal or n-alkanes. In the molecules of alkanes all Carbon atoms are in the state of sp3-hybridization. The distance between two Carbon atoms is 0.154 nm, but the distance between two atoms of Carbon and Hydrogen is 0.110 nm. The rotation can take place around C—C bonds. As the result of this rotation the molecule have different conformations (spatial forms).

7. Crystal n-alkanes are zigzag-shaped. This conformation is the most advantageous for the molecule.

8. 3. Nomenclature of Alkanes Some alkanes have trivial names. Methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, and neopentane are trivial names. Other alkanes have IUPAC names in which the number of carbon atoms in the chain is specified by a Latin or Greek prefix preceding the suffix -ane, which identifies the compound as a member of the alkane family. IUPAC Names of Unbranched Alkanes

9. IUPAC Rules: Nomenclature of Branched Alkanes 1. To chose the longest Carbon chain in the molecule. 2. To identify the substituent groups attached to the parent chain.

10. 3. To number the longest chain in the direction that gives the lowest number to the substituent group at the first point of branching. If in molecule there are two and more similar substituents on the equal distance from the ends of the longest chain, it is necessary to begin the numbering from the end of Carbon chain where there are more substituents.

11. When the same substituent appears more than once, use the multiplying prefixes di-, tri-, tetra-, and so on. When two or more different substituents are present, they are listed in alphabetical order in the name. 4-ethyl-3-methyloctane

12. 4. The Isomery of Alkanes In the molecules of organic compounds the atom of Carbon is connected with the atom of Carbon or the atom of Hydrogen. There are the primary, the secondary, the tertiary and the quaternary carbon atoms. The primary carbon atom is the atom which is connected only with one atom of carbon. The secondary carbon atom is the atom which is connected with two atoms of carbon. The tertiary carbon atom is the atom which is connected with three atoms of carbon. The quaternary carbon atom is the atom which is connected with four atoms of carbon. 1,2,3,4,5 – primary; 6 – secondary; 7 – tertiary; 8 – quaternary.

13. Alkanes are characterized by structural and optical isomery. Structural isomery is formed by different sequence of Carbon atom connections (isomery of the Carbon chain). Methane is the only alkane of molecular formula CH4, ethane the only one that is C2H6, and propane the only one that is C3H8. Beginning with C4H10 constitutional isomers are possible; two alkanes have this particular molecular formula. In one, called n-butane, four carbons are joined in a continuous chain. The second isomer has a branched carbon chain and is called isobutane.

14. Methane is the lowest boiling alkane, followed by ethane, then propane. n-butane and isobutane have the same molecular formula but differ in the order in which their atoms are connected. They are constitutional isomers of each other. Because they are different in structure, they can have different properties. Both are gases at room temperature, but n-butane boils almost 10C higher than isobutane and has a melting point that is over 20C higher.

15. The number of isomers increases enormously with the number of carbon atoms in the carbon chain. The Number of Constitutionally Isomeric Alkanes of Particular Molecular Formulas

16. Optical isomery is characteristic for alkanes contain 7 and more carbon atoms.

17. 5. The methods of extraction of alkanes The main natural sources of alkanes are petroleum and gas. Petroleum is the complex mixture of organic compounds; the main components of petroleum are branched and normal alkanes. Gas consists of gaseous alkanes — methane (95%), ethane, propane, butane. For receiving alkanes from petroleum it is necessary to use fractional distillation. As the result several fractions are received: This table lists that each fraction is the mixture of hydrocarbons which have equal points of boiling temperature. Gas is shared to its components by fractional distillation too.

18. The artificial methods of extraction of alkanes 1. Hydration of carbon (II) oxide. The mixture of CO and H2 is heated at temperature 180-300C. In this reaction catalysts are Fe and Co). As the result the mixture of n-alkanes appears. This method is often used in industry for receiving of artificial benzine.

19. 2. Hydration of alkenes and alkynes. In these reactions catalysts are Pt, Pd and Ni.

20. 3. Vurts reaction 4. Allowing of salts of carboxylic acids and alkalis.

21. 6. Physical properties of alkanes The first four alkanes in homological row are gaseous at room temperature. The unbranched alkanes pentane (C5H12) through heptadecane (C17H36) are liquids, whereas higher homologs are solids. The boiling points of unbranched alkanes increase with the number of carbon atoms. Branched alkanes have lower boiling points than their unbranched isomers. Isomers have the same number of atoms and electrons, but a molecule of a branched alkane has a smaller surface area than an unbranched one. The extended shape of an unbranched alkane permits more points of contact for intermolecular associations.

22. Solid alkanes are soft, generally low-melting materials.All alkanes are insoluble in water. Being insoluble, and with densities in the 0.6-0.8 g/mL range, alkanes float on the surface of water. The exclusion of nonpolar molecules, such as alkanes, from water is called the hydrophobic effect. The most alkanes are dissoluble in organic solvents — diethyl ether, CCl4, benzol. Their insolubility increases with the increasing of number of carbon atoms in the molecule.Gaseous and solid alkanes don’t smell. But liquids have “benzine” smell.

23. 7. Chemical properties of alkanes In normal conditions alkanes do not react with acids and alkalis because -bonds in their molecules are very strong. Butalkanes take part in such reactions as: -reactions of the substitution; -reactions of the oxidation; -reactions of the destruction.

24. I. Reactions of the radical substitution 1. Halogenation of alkanes. Alkanes react with halogens (except I2).

26. 3. Nitration of alkanes. 2. Sulfochloration of alkanes.

27. II. Reactions of the oxidation CH4 + 2O2 → CO2 + 2H2O Alkanes can burn if oxygen is present. As the result H2O and CO2 appear.

28. III. Reactions of the destruction CH3−CH3 → CH2=CH2 + H2 CH3−CH2−CH2−CH3 → CH4 + CH2=CH−CH3 CH3−CH3 + CH2=CH2 Cracking is the destroying of ­­some −C−C− and −C−H bonds in the molecule of alkanes at high temperature.

29. 8. Structure of Cycloalkanes Cycloalkanes are hydrocarbons in which all Carbon atoms form the cycle and are in the state of sp3-hybridization. Cycloalkanes are saturated hydrocarbons. Cycloalkanes have the general molecular formula CnH2n.

30. Early chemists observed that cyclic compounds found in nature generally had five- or sixmembered rings. Compounds with three- and fourmembered rings were found much less frequently. This observation suggested that compounds with five- and sixmembered rings were more stable than compounds with three- or fourmembered rings.

31. In 1885, the German chemist Adolf von Baeyer proposed that the instability of three- and fourmembered rings was due to angle strain. We know that, ideally, an sp3-hybridized carbon has bond angles of 109.5°. Baeyer suggested that the stability of a cycloalkane could be predicted by determining how close the bond angle of a planar cycloalkane is to the ideal tetrahedral bond angle of 109.5°. The angles in an equilateral triangle are 60°. The bond angles in cyclopropane, therefore, are compressed from the ideal bond angle of 109.5° to 60°, a 49.5° deviation. This deviation of the bond angle from the ideal bond angle causes strain called angle strain.

32. orbitals in cyclopropane can’t point directly at each other, they have shapes that resemble bananas and, consequently, are often called banana bonds. In addition to possessing angle strain, threemembered rings have torsional strain because all the adjacent −C−H bonds are eclipsed. The angle strain in a three-membered ring can be appreciated by looking at the orbitals that overlap to form the σ-bonds in cyclopropane. Normal σ-bonds are formed by the overlap of two sp3-orbitals that point directly at each other. In cyclopropane, overlapping orbitals cannot point directly at each other. Therefore, the orbital overlap is less effective than in a normal −C−C− bond. The less effective orbital overlap is what causes angle strain, which in turn causes the −C−C− bond to be weaker than a normal −C−C− bond. Because the −C−C− bonding

33. The bond angles in planar cyclobutane would have to be compressed from 109.5° to 90°, the bond angle associated with a planar four-membered ring. Planar cyclobutane would then be expected to have less angle strain than cyclopropane because the bond angles in cyclobutane are only 19.5° away from the ideal bond angle.

34. Baeyer predicted that cyclopentane would be the most stable of the cycloalkanes because its bond angles (108°) are closest to the ideal tetrahedral bond angle. He predicted that cyclohexane, with bond angles of 120°, would be less stable and that as the number of sides in the cycloalkanes increases, their stability would decrease.

35. Contrary to what Baeyer predicted, cyclohexane is more stable than cyclopentane. Furthermore, cyclic compounds do not become less and less stable as the number of sides increases. The mistake Baeyer made was to assume that all cyclic molecules are planar. Because three points define a plane, the carbons of cyclopropane must lie in a plane. The other cycloalkanes, however, are not planar.

36. Cyclic compounds twist and bend in order to attain a structure that minimizes the three different kinds of strain that can destabilize a cyclic compound: Angle strain is the strain induced in a molecule when the bond angles are different from the ideal tetrahedral bond angle of 109.5°. Torsional strain is caused by repulsion between the bonding electrons of one substituent and the bonding electrons of a nearby substituent. Steric strain is caused by atoms or groups of atoms approaching each other too closely.

37. Although planar cyclobutane would have less angle strain than cyclopropane, it could have more torsional strain because it has eight pairs of eclipsed hydrogens, compared with the six pairs of cyclopropane. So cyclobutane is not a planar molecule—it is a bent molecule. One of its methylene groups is bent at an angle of about 25° from the plane defined by the other three carbon atoms. This increases the angle strain, but the increase is more than compensated for by the decreased torsional strain as a result of the adjacent hydrogens not being as eclipsed, as they would be in a planar ring.

38. If cyclopentane were planar, as Baeyer had predicted, it would have essentially no angle strain, but its 10 pairs of eclipsed hydrogens would be subject to considerable torsional strain. So cyclopentane puckers, allowing the hydrogens to become nearly staggered. In the process, however, it acquires some angle strain. The puckered form of cyclopentane is called the envelope conformation because the shape resembles a squarish envelope with the flap up.

39. The classification of cycloalkanes

41. 9. Nomenclature of Cycloalkanes Cycloalkanes are almost always written as skeletal structures. Skeletal structures show the carbon–carbon bonds as lines, but do not show the carbons or the hydrogens bonded to carbons. Atoms other than carbon and hydrogens bonded to atoms other than carbon are shown. Each vertex in a skeletal structure represents a carbon. It is understood that each carbon is bonded to the appropriate number of hydrogens to give the carbon four bonds.

42. The rules for naming cycloalkanes resemble the rules for naming acyclic alkanes: In the case of a cycloalkane with an attached alkyl substituent, the ring is the parent hydrocarbon unless the substituent has more carbon atoms than the ring. In that case, the substituent is the parent hydrocarbon and the ring is named as a substituent. There is no need to number the position of a single substituent on a ring.

43. If the ring has two different substituents, they are cited in alphabetical order and the number 1 position is given to the substituent cited first.

44. If there are more than two substituents on the ring, they are cited in alphabetical order. The substituent given the number 1 position is the one that results in a second substituent getting as low a number as possible. If two substituents have the same low number, the ring is numbered—either clockwise or counterclockwise—in the direction that gives the third substituent the lowest possible number. For example, the correct name of the following compound is 4-ethyl-2-methyl-1-propylcyclohexane, not 5-ethyl-1-methyl-2-propylcyclohexane:

45. 10. Conformation of cycloalkanes The cyclic compounds most commonly found in nature contain sixmembered rings because such rings can exist in a conformation that is almost completely free of strain. This conformation is called the chair conformation. In the chair conformer of cyclohexane, all the bond angles are 111°, which is very close to the ideal tetrahedral bond angle of 109.5°, and all the adjacent bonds are staggered.

46. Cyclohexane can also exist in a boat conformation. Like the chair conformer, the boat conformer is free of angle strain. However, the boat conformer is not as stable as the chair conformer because some of the bonds in the boat conformer are eclipsed, giving it torsional strain. The boat conformer is further destabilized by the close proximity of the flagpole hydrogens (the hydrogens at the “bow” and “stern” of the boat), which causes steric strain.

47. When the carbon is pulled down just a little, the twist-boat (or skew-boat) conformer is obtained. The twist-boat conformer is more stable than the boat conformer because there is less eclipsing and, consequently, less torsional strain and the flagpole hydrogens have moved away from each other, thus relieving some of the steric strain.

48. When the carbon is pulled down to the point where it is in the same plane as the sides of the boat, the very unstable half-chair conformer is obtained. Pulling the carbon down farther produces the chair conformer. The graph in figure shows the energy of a cyclohexane molecule as it interconverts from one chair conformer to the other; the energy barrier for interconversion is 12.1 kcal/mol (50.6 kJ/mol). From this value, it can be calculated that cyclohexane undergoes 10 ring flips per second at room temperature. In other words, the two chair conformers are in rapid equilibrium.

50. Because the chair conformers are the most stable of the conformers, at any instant more molecules of cyclohexane are in chair conformations than in any other conformation. It has been calculated that, for every thousand molecules of cyclohexane in a chair conformation, no more than two molecules are in the next most stable conformation—the twist-boat.