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Chemical Ideas 12 Organic chemistry frameworks

Chemical Ideas 12 Organic chemistry frameworks. 12.1 Alkanes. Many carbon compounds are found in living organisms, this why their study is named organic chemistry. Carbon is unique About 7 million compounds containing carbon and hydrogen are known to chemists

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Chemical Ideas 12 Organic chemistry frameworks

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  1. Chemical Ideas 12Organic chemistry frameworks 12.1 Alkanes

  2. Many carbon compounds are found in living organisms, this why their study is named organic chemistry

  3. Carbon is unique About 7 million compounds containing carbon and hydrogen are known to chemists This is far more than the number of compounds from all the other elements put together

  4. Electron structure makes it the first member of Gp 4 in the centre of the periodic table – this is responsible for its special properties Carbon atom has 4 electrons in its outer shell – too many to lose or gain – the ions would have +4 or -4 (too highly charged) All carbon compounds are covalent rather than ionic Methane(CH4) C shares 4 electrons with 4 H atoms Carbon forms strong covalent bonds with itself to form rings and chains this is called catenation Each C atom can form 4 covalent bonds- chains may be straight or branched and can have other atoms or groups substituted on to them Why carbon? H   H  C  H   H

  5. Hydrocarbons • Only contain carbon and hydrogen • General formula CXHY Methane –CH4 is an alkane Ethene C2H4 is an alkene Benzene C6H6 is an arene H l H - C - H l H

  6. Alkanes • Saturated hydrocarbons • Contain C and H only • Contain single bonds C-C • Have 4 bonds to every carbon (C) atom • Are non polar • General formula CnH2n+2 • Physical properties such as m.pt,b.pt and density change as the number of carbon atoms in the molecule increase

  7. Alkanes Names of all alkanes end in -ane shortened Name # carbons Structural Formula Methane 1 CH4 Ethane 2 CH3CH3 Propane 3 CH3CH2CH3 Butane 4 CH3CH2CH2CH3 Pentane 5 CH3CH2CH2CH2CH3

  8. Alkanes Names of all alkanes end in -ane shortened Name # carbons Structural Formula Hexane 6 CH3CH2CH2CH2CH2CH3 Heptane 7 CH3CH2CH2CH2CH2CH2CH3 Octane 8 CH3CH2CH2CH2CH2CH2CH2CH3 Nonane 9 CH3 CH2 CH2CH2CH2CH2CH2CH2CH3 Decane 10 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3 A series of compounds which are related in this way are called ahomologous series

  9. Finding the formula of alkanes Molecular formula = m x empirical formula Where m is 1,2,3,…… • For hydrocarbons , composition of mass is easily found by burning a known mass in oxygen, measuring the amounts of CO2 and H2O this is called combustion analysis

  10. Finding the formula of alkanes Example 0.100g of hydrocarbon X on complete combustion gave 0.309g CO2 and H2O 0.142g calculate the empirical formula of X Answer 1st calc the masses of C and H in 0.100g 44g CO2 contains 12g of C mass of C in 0.100g X = (12/44) x 0.309g = 0.0843g 18g H2O contains 2g H mass of H in 0.100g X = (2/18) x 0.142g = 0.0158g

  11. Finding the formula of alkanes C H Ratio by mass 0.0843 : 0.0158 Ratio by moles 0.00703 : 0.0158 Simplest by ratio(÷ by smaller) 1 : 2.25 Whole number ratio 4 : 9 Empirical formula = C4H9

  12. Finding the formula of alkanes Example Relative molecular mass of X was found to be 114 by using a mass spectrometer Answer Empirical formula of X is C4H9 but MrC4H9 = 57 this is ½ of 114. So the molecular formula of X must be (C4H9)2 = C8H18

  13. Structure of alkanes • Full structural formula of methane Shows all atoms and bonds • Propane • Shortened structural formula for propane • Further shortened to

  14. Structure of alkanes

  15. Alkyl Groups Branches on carbon chains H H C CH3 methyl H H H H C C CH3CH2 ethyl H H

  16. Naming organics – nomenclature Ref. P136 Organic Chemistry Solomons and Fryhle 2002 International Union of Pure and Applied Chemistry – IUPAC – has an internationally agreed and accepted method for giving evey organic molecule a unique name using a method - you are going to be examined on your ability to use this methodology. It is worth spending time learning and practicing this skill. Very useful indeed. The method is fairly easy and stepwise as follows:

  17. Naming organics – nomenclature Ref. P136 Organic Chemistry Solomons and Fryhle 2002 1. Locate the longest continuous chain of carbon atoms; this chain determines the parent name for the alkane – this may not always be obvious since they go around corners!

  18. Naming organics - nomenclature 2. Number the longest chain beginning with the end of the chain nearer the substituent

  19. Naming organics - nomenclature 3. Use the numbers obtained from rule 2 to designate the location of the substituent group

  20. Naming organics - nomenclature 4. When there are more than one group on different parts of the chain – number from the longest chain for example we call this “4-ethyl-2-methylhexane”

  21. Naming organics - nomenclature 5. When two substituents are on the same carbon atom, use that number twice for example, this is 3-ethyl-3methylhexane

  22. Naming organics - nomenclature 6. When two or more substituents are identical, indicate this by the use of the prefixes di-, tri-, tetra-, and so on. Make sure every substituent has a number. Commas separate numbers from each other. 2,3-dimethylbutane

  23. Naming organics - nomenclature 7. Classification of hydrogen atoms 2-methyl butane has primary (1o), secondary (2o) and tertiary (3o) hydrogens

  24. Naming organics - nomenclature 8. If there is a halide group – p140 – number from the first substituent attached to it regardless of whether it is halo or alkyl. If they are equal distance, then go alphabetically.

  25. Naming alkenes - nomenclature 1. For alkenes, determine the parent by selecting the longest chain that contains the double bond and change the ending of the name from “–ane” to “-ene”

  26. Naming alkenes - nomenclature 2. Number the chain so as to include both carbon atoms of the double bond and begin naming numbering at the end of the chain nearest the location of the double bond

  27. Naming alkenes - nomenclature 3. Number the other substituents as we have already learned.

  28. Naming alcohols – nomenclature (p141) In what is called IUPAC substitutive nomenclature a name may have as many as 4 features! Locant, prefix, parent compound and one suffix….(continuted)

  29. Naming alcohols – nomenclature …For the alcohols, you add “-ol” to the suffix, in general, numbering of the chain always begins at the end nearer the group named as a suffix.

  30. Naming alcohols – nomenclature (p141) 1. Select the longest chain again to which the hydroxyl (OH) group is attached. Change the name of the alkane corresponding to this chain by dropping the “e” and adding the suffix “ol”

  31. Naming alcohols – nomenclature (p141) 2. Number the longest continuous chain so as to give the carbon atom bearing the hydroxyl group the lower number.

  32. Naming Summary 1. Count the C’s in the longest chain 2. Name each attached group 3 Count the longest carbon chain to give the first attached group the smallest number 4. Name and locate each group

  33. Naming Branched Alkanes CH3 methyl branch CH3CH2CH2CHCH2CH3 6 5 4 3 2 1 Count 3-Methylhexane on third C CH3 six carbon chain group

  34. Branched alkanes -Isomers • Same molecular formula • Same number and types of atoms • Different arrangement of atoms

  35. Cycloalkanes • The is a group of alkanes that have a cyclic structure. • These cycloalkanes contain a carbon chain that is in a ring. • Each cycloalkane has a formula that is 2C less than the corresponding alkane. • For example, propane is C3H8 whereas cyclopropane ic C3H6. Butane is C4H10 and cyclobutane is C4H10. • The names of the cyclic structures use the prefix cyclo in from of the alkane name for the carbon chain Cyclopropane CH2 CH2 CH2 Cyclobutane CH2 CH2 CH2 CH2

  36. More Cycloalkanes Cyclopentane CH2 CH2 CH2 CH2 CH2 Cyclohexane CH2 CH2 CH2 CH2 CH2 CH2

  37. Shapes of alkanes Pairs of electrons in the bonds repel each other so in all covalent compounds the bonds are as far away from each other as possible. The bond angle for H-C-H is 109 represents a bond in the plane of the paper represents a bond in a direction behind the plane of the paper represents a bond in a direction in front of the plane of the paper

  38. Shapes of alkanes Ethane Each carbon atom is at the centre at of a tetrahedral arrangement a simpler way of drawing ethane which shows the shape less accurately

  39. Shapes of alkanes Hydrocarbon chains are not really straight but a zig-zag of carbon atoms. All bond angles are 109◦

  40. Reaction of alkanes • Oxidation are v. unreactive unaffected by acids and alkalis and oxidising agents • When they do react it is usually in the gas phase and energy needs to be supplied to get the reaction started

  41. Reaction of alkanes Combustion alkane + O2 CO2 + H2O + heat C6H14 + 9 1/2 O2 6CO2 + 7H2O + heat • If air supply is limited combustion in incomplete and products include CO and C (soot) along with partially oxidised hydrocarbons

  42. Action of heat on alkanes • When alkanes fractions are heated under different conditions,3 different reactions can occur, isomerisation, reforming and cracking

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