Hydrocarbons 1 st stage Wrea Mohammed

1. Hydrocarbons 1st stage Wrea Mohammed

2. Classification of Hydrocarbon

3. Hydrocarbons: • Are compounds made up of only the elements carbon and hydrogen. • They may be aliphatic or aromatic. • [1] Aliphatic hydrocarbons. The word aliphatic is derived from the Greek word aleiphasmeaning fat. Aliphatic compounds have physical properties similar to fats. • Aliphatic hydrocarbons can be divided into three subgroups. • Alkaneshave only C – C σ bonds and no functional group. Methane, CH4, is a simple alkane. • Alkeneshave a C = C double bond as a functional group. Ethylene, CH2 = CH2, is a simple alkene.

4. Alkyneshave a C ≡ C triple bond as a functional group. Acetylene, HC ≡ CH, is a simple alkyne. • [2]Aromatic hydrocarbons (Arenes) • The simplest aromatic hydrocarbon is benzene. The six-membered ring and three π bonds of benzene comprise a single functional group. Benzene is a component of the BTX mixture (B for benzene, T for toluene and X for xylene) added to gasoline to boost octane ratings.

6. alkanes • alkanes are aliphatic hydrocarbons having only C–C and C–H σ bonds. Because their carbon atoms can be joined together in chains or rings. • They can be categorized as acyclic or cyclic. • Acyclic alkanes have the molecular formula ( CnH2n+2 )(where n = an integer) and contain only linear and branched chains of carbon atoms. They are also called saturated hydrocarbons because they have the maximum number of hydrogen atoms per carbon. Like methane, ethane, propane…..etc.

7. Methane, CH4, has a single carbon atom, and ethane, CH3CH3, has two. All C atoms in an alkane are surrounded by four groups, making them sp3 hybridized and tetrahedral, and all bond angles are 109.5°.

8. The three-carbon alkane CH3CH2CH3, called propane, has molecular formula C3H8. Each carbon in the three-dimensional drawing has two bonds in the plane (solid lines), one bond in front (triangle shape), and one bond behind the plane (on a dashed line). • In propaneand higher molecular weight alkanes, the carbon skeleton can be drawn in a variety of different ways and still represent the same molecule.

9. Structural formulas • Structural formulas show the arrangement of atoms in an organic compound. • In expanded structural formulas, all the individual bonds are drawn. • In condensedstructural formulas, each carbon is written with the H atoms connected to it. • The geometrical arrangement of carbon atoms is not a straight line. • H H • || • H — C — = CH3 — — C — = — CH2 — • | | • H H Condensed structure Condensed structure Geometrical arrangement Expanded structure Expanded structure

10. Acyclic alkanes have a general formula of CnH2n +2. C Atoms H Atoms Formula Name 12x1 + 2 = 4 CH4 Methane 32x3 + 2 = 8 C3H8 Propane 62x6 + 2 = 14 C6H14 Hexane 8 2x8 + 2 = 18 C8H18Octane 10 2x10 + 2 = 22 C10H22 Decane

11. Classification of Carbon Atoms • Carbon atoms in alkanes and other organic compounds are classified by the number of other carbons directly bonded to them.

12. Classification of Hydrogen Atoms • Hydrogen atoms are classified as primary (1°), secondary (2°), or tertiary (3°) depending on the type of carbon atom to which they are bonded.

13. Homologous series • A group of compounds that differ by only a CH2group • A CH2group is called a methylene group.

14. Constitutionalor structuralIsomers • Two different compounds with the same molecular formula. • Constitutional isomers differ in the way the atoms are connected to each other. • Example 1: There are two different ways to arrange four carbons, giving two compounds with molecular formula C4H10, named butane and isobutane.

15. Example 2: There are three constitutional isomers for the five-carbon alkane, each having molecular formula C5H12pentane, isopentane (or 2-methylbutane), and neopentane (or 2,2-dimethylpropane).

16. Example 3 : There are two acceptable arrangements of atoms for the molecular formula C2H6O. • Ethanol and dimethyl ether are constitutional isomers because they have the same molecular formula, but the connectivity of their atoms is different. For example, ethanol has one C – C bond and one O – H bond, whereas dimethyl ether has two C – O bonds.

17. Stereo or Geometric isomers • Different compounds with the same molecular formula, but they represent the second major class of isomers. • Stereoisomers are isomers that differ only in the way the atoms are oriented in space. • The prefixes (cis) and (trans)are used to distinguish these stereoisomers. • The cis isomer has two groups on the same side. • The trans isomer has two groups on opposite sides.

18. There are two different 1,2-dimethylcyclopentanes—one having two CH3groups on the same side of the ring and one having them on opposite sides of the ring.

19. Cis- and trans-1,2-dimethylcyclopentane can also be drawn as if the plane of the ring goes through the plane of the page. Each carbon in the ring then has one bond that points above the ring and one that points below.

20. Naming Substituents • Carbon substituents bonded to a long carbon chain are called alkyl groups (R). • An alkyl group is formed by removing one hydrogen from an alkane. • To name an alkyl group, change the -ane ending of the parent alkane to -yl. Thus, methane (CH4) becomes methyl (CH3 – ) and ethane (CH3CH3) becomes ethyl (CH3CH2 – ). Rdenotes a general carbon group bonded to a functional group. R thus denotes any alkyl group.

21. Example 1 : For example, propane has both 1° and 2° H atoms, and removal of each of these H atoms forms a different alkyl group with a different name, propyl or isopropyl.

22. Example 2 : There are two different butane isomers to begin with, each having two different kinds of H atoms, there are four possible alkyl groups containing four carbon atoms, each having a different name: butyl, sec-butyl, isobutyl, and tert-butyl.

23. Naming Alkanes • In order to give compounds a name, certain rules must be followed. When naming organic compounds, the IUPAC (International Union of Pure and Applied Chemistry) nomenclature is used. • The name of every organic molecule has three parts.

24. Step [1] Find the parent carbon chain and add the suffix. • Find the longest continuous carbon chain, and name the molecule by using the parent name for that number of carbons, To the name of the parent, add the suffix -ane for an alkane. Each functional group has its own characteristic suffix.

25. It does not matter if the chain is straight or has bends. All of the following representations are equivalent.

26. If there are two chains of equal length, select the chain with more substituents. In the following example, two different chains in the same alkane contain 7 C’s, but the compound on the left has two alkyl groups attached to its long chain, whereas the compound to the right has only one.

27. Step [2] Number the atoms in the carbon chain. • Number the longest chain to give the first substituent the lower number.

28. Step [3] Name and number the substituents. • Name the substituents as alkyl groups, and use the numbers from (Step 2) to designate their location.

29. When two or more branched chains are identical, indicate this by the use of the prefixes ‘di-’, ‘tri-’, ‘tetra-’, and so on.

30. Step [4] Combine substituent names and numbers + parent + suffix. • Separate numbers by commas (,) and separate numbers from letters by hyphens (-). The name of an alkane is a single word, with no spaces after hyphens or commas.

31. Sample Problem Give the IUPAC name for the following compound. ethyl at C5 methyl at C2 CH3 CH3 CH3CH2 CH3CH2 H CH3 CH2CH2 C C C CH2CH3 H H CH3 CH3 methyl at C6 1 2 5 6 longest chain is 8 C’s = octane 5-ethyl-2,6-dimethyloctane

33. Give the IUPAC name for each compound. • A- CH3CH2CH(CH3)CH2CH3B- (CH3)3CCH2CH(CH2CH3)2 • C- CH3(CH2)3CH(CH2CH2CH3)CH(CH3)2 • D- 3-methylhexane E- 3,5,5-trimethyloctane E- 3-ethyl-5-isobutylnonane • F- 3,3-dimethylpentane G- 3-ethyl-4-methylhexane