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Organic Chemistry

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  1. Organic Chemistry

  2. Outline • Introduction • Special nature of carbon • Classification of Organic Chemistry • Homologous Series & General Characteristics • Separation of Petroleum & Cracking • Types of formula • Isomerism • I.U.P.A.C Nomenclature • Compounds of different functional groups

  3. Introduction • Organic chemistry is the study of carbon compounds. There are around 6 millions compounds of C already known. • Not all C-compounds are organic • CO, CO2 considered inorganic • Organic compounds covalently bonded compounds containing carbon, excluding carbonates and oxides

  4. Special nature of carbon • Carbon can join with other carbon atoms to form • Long chain carbon atoms • Branch chain carbon atoms • Rings of carbons • Multiple bonds between carbon atoms and atoms of other elements Why is it possible for carbon to do so?

  5. SPECIAL NATURE OF CARBON - CATENATION CATENATION is the ability to form bonds between atoms of the same element. Carbon forms chains and rings, with single, double and triple covalent bonds, becauseit is able toFORM STRONG COVALENT BONDS WITH OTHER CARBON ATOMS Carbon forms a vast number of carbon compounds because of the strength of the C-C covalent bond. Other Group IV elements can do it but their chemistry is limited due to the weaker bond strength. BOND ATOMIC RADIUS BOND ENTHALPY C-C 0.077 nm +348 kJmol-1 Si-Si 0.117 nm +176 kJmol-1 The larger the atoms, the weaker the bond. Shielding due to filled inner orbitals and greater distance from the nucleus means that the shared electron pair is held less strongly.

  6. THE SPECIAL NATURE OF CARBON CHAINSANDRINGS CARBON ATOMS CAN BE ARRANGED IN STRAIGHT CHAINS BRANCHED CHAINS andRINGS You can also get a combination of rings and chains

  7. THE SPECIAL NATURE OF CARBON MULTIPLE BONDING AND SUBSTITUENTS CARBON-CARBON COVALENT BONDS CAN BE SINGLE, DOUBLE OR TRIPLE

  8. THE SPECIAL NATURE OF CARBON MULTIPLE BONDING AND SUBSTITUENTS CARBON-CARBON COVALENT BONDS CAN BE SINGLE, DOUBLE OR TRIPLE DIFFERENT ATOMS / GROUPS OF ATOMS CAN BE PLACED ON THE CARBONS The basic atom is HYDROGEN but groups containing OXYGEN, NITROGEN, HALOGENS and SULPHUR are very common. CARBON SKELETON FUNCTIONAL CARBON SKELETON FUNCTIONAL GROUP GROUP The chemistry of an organic compound is determined by its FUNCTIONAL GROUP

  9. THE SPECIAL NATURE OF CARBON MULTIPLE BONDING AND SUBSTITUENTS ATOMS/GROUPS CAN BE PLACED IN DIFFERENT POSITIONS ON A CARBON SKELETON THE C=C DOUBLE BOND IS IN A DIFFERENT POSITION PENT-1-ENE PENT-2-ENE THE CHLORINE ATOM IS IN A DIFFERENT POSITION 1-CHLOROBUTANE 2-CHLOROBUTANE

  10. Classification of Organic Compounds • Hydrocarbons : Compounds containing carbon and hydrogen only • Non-hydrocarbons : Compounds that may also contain other elements such as nitrogen, sulphur, halogen or oxygen atoms besides hydrogen and carbon.

  11. Homologous Series • A series of compounds with the same general formula (e.g. Alkanes CnH2n+2)and functional group (e.g. C=C, OH) • Each member differs from the next by CH2 • Members have the same chemical properties. • Members show a gradation in physical properties.

  12. Some functional groups

  13. alkene alcohol ketone ester carboxylic acid

  14. carboxylic acid ester aldehyde ether amine nitrile Page 425

  15. Influence of functional groups • bonding and shape • type and strength of intermolecular forces • physical properties • nomenclature • chemical reactivity

  16. Isomerism • Structural Isomers are 2 or more compounds with the same molecular formula but different structural formula. Example : Isomers of butane 1st isomer 2nd isomer Condensed CH3CH2CH2CH3 CH3CH(CH3)CH3 formula (has a branched chain)

  17. Pentane has 3 isomers: 1st isomer 2nd isomer 3rd isomer Condensed formula

  18. Some isomers of C5H12O -OH attached to C-1 • OH attached to C-2 • OH attached to C-3 Many more isomers of alcohol. Some are not alcohol. E.g. ether containing C-O-C as a fn’al group. CH3CH2CH2OCH2CH2CH3 Page 428 Practice Qns

  19. Physical Properties of Alkanes • First 4 members are gases at room temperature & pressure (r.t.p.) • All members are insoluble in water but soluble in organic solvent. Reasons: • Made up of covalent molecules held by weak intermolecular forces, so less energy is required to overcome the forces to separate the molecules. • Like dissolve like Do you expect isomers to have similar physical properties?

  20. Isomers have different physical properties e.g. boiling point or melting point because the different structures will affect the physical properties. Isomers have the same chemical properties because there are the same number and kind of atoms in each isomer.

  21. I.U.P.A.C. NOMENCLATURE A systematic name has two main parts. STEMnumber of carbon atoms in longest chain bearing the functional group + a prefix showing the position and identity of any side-chain substituents. Prefix C atoms Alkane meth- 1 methane eth- 2 ethane prop- 3 propane but- 4 butane pent- 5 pentane hex- 6 hexane hept- 7 heptane oct- 8 octane non- 9 nonane dec- 10 decane Apart from the first four, which have trivial names, the number of carbons atoms is indicated by a prefix derived from the Greek numbering system. The list of alkanes demonstrate the use of prefixes. The ending -ane is the same as they are all alkanes. Working out which is the longest chain can pose a problem with larger molecules.

  22. CH3 CH3 CH2 CH2 CH2 CH3 CH3 CH2 CH3 CH2 CH2 CH3 CH2 CH2 CH2 CH3 CH2 CH2 CH2 CH3 I.U.P.A.C. NOMENCLATURE How long is a chain? Because organic molecules are three dimensional and paper is two dimensional it can be confusing when comparing molecules. This is because... 1. it is too complicated to draw molecules with the correct bond angles 2. single covalent bonds are free to rotate All the following written structures are of the same molecule - PENTANE C5H12 A simple way to check is to run a finger along the chain and see how many carbon atoms can be covered without reversing direction or taking the finger off the page. In all the above there are... FIVE CARBON ATOMS IN A LINE.

  23. CH3 CH3 CH3 CH2 CH2 CH2 CH CH3 CH2 CH3 CH CH2 CH3 CH3 CH3 CH3 CH2 CH CH2 CH CH3 I.U.P.A.C. NOMENCLATURE How long is the longest chain? Look at the structures and work out how many carbon atoms are in the longest chain. THE ANSWERS ARE ON THE NEXT SLIDE

  24. CH3 CH3 CH3 CH2 CH2 CH2 CH CH3 CH2 CH3 CH CH2 CH3 CH3 CH3 CH3 CH2 CH CH2 CH CH3 I.U.P.A.C. NOMENCLATURE How long is the longest chain? Look at the structures and work out how many carbon atoms are in the longest chain. LONGEST CHAIN = 5 LONGEST CHAIN = 6 LONGEST CHAIN = 6

  25. I.U.P.A.C. NOMENCLATURE A systematic name has two main parts. SUFFIXAn ending that tells you which functional group is present See if any functional groups are present. Add relevant ending to the basic stem. In many cases the position of the functional group must be given to avoid any ambiguity Functional group Suffix ALKANE - ANE ALKENE - ENE ALKYNE - YNE ALCOHOL - OL ALDEHYDE - AL KETONE - ONE ACID - OIC ACID 1-CHLOROBUTANE 2-CHLOROBUTANE SUBSTITUENTSMany compounds have substituents (additional atoms, or groups) attached to the chain. Their position is numbered.

  26. I.U.P.A.C. NOMENCLATURE SIDE-CHAINcarbon based substituents are named before the chain name. they have the prefix -yl added to the basic stem (e.g. CH3 is methyl). Number the principal chain from one end to give the lowest numbers. Side-chain names appear in alphabetical order butyl, ethyl, methyl, propyl Eachside-chain is given its own number. If identical side-chains appear more than once, prefix with di, tri, tetra, penta, hexa Numbers are separated from names by a HYPHEN e.g. 2-methylheptane Numbers are separated from numbers by a COMMA e.g. 2,3-dimethylbutane Alkyl radicals methyl CH3 - CH3 ethyl CH3- CH2- C2H5 propyl CH3- CH2- CH2- C3H7

  27. CH3 CH3 CH CH3 CH2 CH2 CH2 CH3 CH CH2 CH3 CH2 CH2 CH I.U.P.A.C. NOMENCLATURE SIDE-CHAINcarbon based substituents are named before the chain name. they have the prefix -yl added to the basic stem (e.g. CH3 is methyl). Number the principal chain from one end to give the lowest numbers. Side-chain names appear in alphabetical order butyl, ethyl, methyl, propyl Eachside-chain is given its own number. If identical side-chains appear more than once, prefix with di, tri, tetra, penta, hexa Numbers are separated from names by a HYPHEN e.g. 2-methylheptane Numbers are separated from numbers by a COMMA e.g. 2,3-dimethylbutane Example longest chain 8 (it is an octane) 3,4,6 are the numbers NOT 3,5,6 order is ethyl, methyl, propyl 3-ethyl-5-methyl-4-propyloctane Alkyl radicals methyl CH3 - CH3 ethyl CH3- CH2- C2H5 propyl CH3- CH2- CH2- C3H7

  28. CH3 CH3 CH3 CH2 CH2 CH2 CH CH3 CH2 CH3 CH CH2 CH3 CH3 CH3 CH3 CH2 CH CH2 CH CH3 I.U.P.A.C. NOMENCLATURE Apply the rules and name these alkanes THE ANSWERS ARE ON THE NEXT SLIDE

  29. CH3 CH3 CH3 CH2 CH2 CH2 CH CH3 CH2 CH3 CH CH2 CH3 CH3 CH3 CH3 CH2 CH CH2 CH CH3 I.U.P.A.C. NOMENCLATURE I.U.P.A.C. NOMENCLATURE Apply the rules and name these alkanes

  30. CH3 CH3 CH3 CH2 CH2 CH2 CH CH3 CH2 CH3 CH CH2 CH3 CH3 CH3 CH3 CH2 CH CH2 CH CH3 I.U.P.A.C. NOMENCLATURE I.U.P.A.C. NOMENCLATURE Apply the rules and name these alkanes Longest chain = 5 so it is a pentane A CH3, methyl, group is attached to the third carbon from one end... 3-methylpentane

  31. CH3 CH3 CH3 CH2 CH2 CH2 CH CH3 CH2 CH3 CH CH2 CH3 CH3 CH3 CH3 CH2 CH CH2 CH CH3 I.U.P.A.C. NOMENCLATURE I.U.P.A.C. NOMENCLATURE Apply the rules and name these alkanes Longest chain = 5 so it is a pentane A CH3, methyl, group is attached to the third carbon from one end... 3-methylpentane Longest chain = 6 so it is a hexane A CH3, methyl, group is attached to the second carbon from one end... 2-methylhexane

  32. CH3 CH3 CH3 CH2 CH2 CH2 CH CH3 CH2 CH3 CH CH2 CH3 CH3 CH3 CH3 CH2 CH CH2 CH CH3 I.U.P.A.C. NOMENCLATURE I.U.P.A.C. NOMENCLATURE Apply the rules and name these alkanes Longest chain = 5 so it is a pentane A CH3, methyl, group is attached to the third carbon from one end... 3-methylpentane Longest chain = 6 so it is a hexane A CH3, methyl, group is attached to the second carbon from one end... 2-methylhexane Longest chain = 6 so it is a hexane CH3, methyl, groups are attached to the third and fourth carbon atoms (whichever end you count from). 3,4-dimethylhexane Discuss examples Page 430

  33. Name the following hydrocarbons: • C(CH3)4 • CH3CH(C2H5)CH3 • CH3CH2CH(C2H5)CH2CH3

  34. Alkanes • Belongs to the homologous series of saturated hydrocarbons • Contain only single covalent bonds between atoms in molecules. • Contain only hydrogen and carbon atoms

  35. Alkanes • Alkanes hydrocarbons that contain only single bonds • Each one different from previous by 1 C and 2 H

  36. General Characteristics • Can be represented by a general formula. • Physical property changes gradually as the number of CH2 group increases. • Have similar chemical properties (since they have the same functional groups)

  37. For alkanes with 3 or less C atoms, only 1 molecular structure possible • In alkanes with more than 3, chains can be straight or branched • So, alkanes with 4 or more C have structural isomers

  38. Alkanes Name ends with –ane and has a general molecular formula CnH2n+2

  39. Physical states • Alkanes with lowest molecular mass (1-4 C atoms) are gases • Natural gasfossil fuel made primarily of alkanes containing 1-4 C atoms • C-H bonds are nonpolar • Only forces of attraction between nonpolar molecules are weak intermolecular forces

  40. The strength of the forces is related to the no. of electrons involved in the structure and the surface area of the molecules over which the interactions can be spread. • Increasing the chain length of the molecules increase both these features and so the strength of the van der Waals’ forces increases with the increasing molecuar size. • Physical properties dependent on these interactions, such as mpt, bpt and enthalpy of vaporisation will also increase with the length of chain.

  41. Larger alkanes are liquid • Gasoline, kerosene made mostly of liquid alkanes • Stronger forces hold together enough to form liquids • Alkanes with very high molecular mass are solid • Paraffin wax contains solid alkanes (candles)

  42. Boiling points • Increase with increasing molecular mass • As the strength of the van der Waals’ forces increases, more energy (heat) required to break them • This property used in separation of petroleum (major source of alkanes) • Petroleum complex mixture of different hydrocarbons that varies greatly in composition

  43. Separation of Petroleum Petroleum is a mixture of hydrocarbon molecules from 1 to more than 50 C atoms is heated in a furnace. Oil vaporizes and passes up the fractionating column. The different fractions come out of the column at different heights depending on their boiling points. Substances with low boiling points are collected near the top of the column A hydrocarbon with a long chain has __________________than one with a shorter carbon chain higher boiling point

  44. General Properties • As the no. of C atoms • increases, • boiling point increases • liquids are more viscous • liquids burn less easily

  45. Cracking • To meet the demands for fractions like petrol and kerosene, a process called cracking is carried out. • This involves the use of high temperature, pressure and catalyst to split the larger molecules (of higher boiling points) into smaller ones (of lower boiling points) • Example C10H2  C10H22 +C10H22

  46. Alkenes • Belongs to the homologous series of unsaturated hydrocarbons. • Contains double covalent bonds between C atoms in molecules. • Contain only H and C atoms. Draw the dot and cross diagram of ethene

  47. Alkenes Important plant hormone – induces flowering and ripening of fruit

  48. Isomerism Butene has 3 isomers: 1st isomer 2nd isomer 3rd isomer Condensed formula

  49. Draw all the isomers of C5H10 and write their condensed formulae. Page 440