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Unit 3 Organic Chemistry. Chapter 8. STSE. The Medicine Hunter p 307. Homework. Review p 308, questions 1-25. Organic compounds.
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Unit 3 OrganicChemistry Chapter 8
STSE • The Medicine Hunter p 307
Homework • Review p 308, questions 1-25
Organic compounds • “What we normally think of as ‘life’ is based on chains of carbon atoms, with a few other atoms, such as nitrogen or phosphorous. One can speculate that one might have life with some other chemical basis…. But carbon seems the most favourable case, because it has the richest chemistry” – Stephen Hawkins
Alkanes • Historically, organic and inorganic was distinguished by the living origin. • It is now the study of carbon compounds. • Only a few carbon compounds are inorganic such as carbon monoxide, CO, carbon dioxide, CO2, and hydrogen cyanide, HCN. • Many complex carbon-based molecules are involves in complex tasks: DNA, cell membranes etc.
Alkanes • Carbon has 4 valence electrons and tends to form 4 covalent bonds, often with hydrogen but also with oxygen, nitrogen, sulfur and the halogens. • Carbon can also bind with itself in single, double and triple bonds. • Most fuels are hydrocarbons, which consist only of carbon atoms and hydrogen atoms connected by covalent bonds.
Alkanes • Alkanes are saturated hydrocarbons, molecules in which all bonds between carbon atoms are single bonds. • The simplest is methane, CH4.
Straight chain hydrocarbons • Alkanes in which the carbon atoms form long chains are called straight-chain alkanes. • The angle between two successive carbons is 109.5o, creating a zigzag configuration. • The general formula of alkanes is CnH2n+2.
Cyclicalkanes • Not all alkanes are based on a straight chain, carbon atoms can also join to form a ring. Cyclopropane is the simplest cyclic alkane, a triangle with 60o angles. The general formula of cycloalkanes is CnH2n.
Structural isomerism • Some hydrocarbons contain one or more hydrocarbon chain called alkyl group. • Those alkyl groups are types of substituent groups, which replace hydrogen in an organic molecule. • Structural isomerism happens when 2 molecules have the same number and types of atoms but they are bonded in a different way.
Mini investigation • Arrangingcarbonatoms p 314
Namingalkanes • Prefix + root + suffix • The prefix gives the position and name of any substituents • The root indicates the number of carbon atoms in the longest continuous chain of carbon atoms • The suffix indicates the type of organic molecule
Namingalkanes • Steps: • Identify the root • Identify the suffix (-ane for alkanes) • Identify the prefix (-yl for alkyls), use the smallest possible numbers, order alphabetically, separate numbers with comas, number/letters with hyphens
Naming cycling alkanes • Steps: • Identify the root, add cyclo • Identify the suffix (-ane for cycloalkanes) • Identify the prefix (-yl for alkyls), no starting point, use the numbering that leads to the lowest number
Drawingalkanes • 4-ethyl-3,5-dimethylnonane
Drawingalkanes • 7-ethyl-2-methyl-4-propyldecane
Drawingalkanes • 1-ethyl-2-propylcyclobutane
Homework • Practice p 320 questions 1, 2
Properties of alkanes • Carbon and hydrogen have similar electronegativity, which means that the molecules are very close to being non-polar. • Van der Walls forces are the main forces in hydrocarbon, resulting in low boiling and melting points. • The boiling points tends to be related to the length of the carbon chain, the longer the chain, the higher the boiling point.
Refining and using organic compounds • Many synthetic materials are made from organic compounds whose main source is petroleum. • Petroleum is a complex mixture of hydrocarbons that require conversion at oil refineries. • The first step involves fractional distillation, based on the different boiling points of each fraction.
Reaction of alkanes • Petrochemicals are formed through reactions called cracking and reforming. • In cracking, the hydrocarbon is heated under pressure in the absence of air, resulting in smaller molecules. • Reforming uses heat, very high pressure and catalysts to convert straight chain alkanes into longer chains.
Reaction of alkanes • In general, alkanes are fairly unreactive, which makes them valuable as lubricating materials and as the backbone for structural materials such as plastics. • Alkanes are used as fuel because their complete combustion releases a lot of energy.
Reaction of alkanes • While carbon dioxide is naturally occurring, too much carbon dioxide contributes to global warming. • If the supply of oxygen is too low, incomplete combustion occurs. • This reaction produces carbon (soot) and carbon monoxide in addition to carbon dioxide and water.
Reaction of alkanes • Alkanes can also undergo a substitution reaction, which produces a halogen containing hydrocarbon derivative.
Homework • Questions 1-10 p 323
Alkene and alkynes • Hydrocarbon containing double and triple bonds are called unsaturated because each carbon contains less than the maximum number of bonds. • A hydrocarbon that contains at least one double bond is called an alkene. • Their general formula is CnH2n. • Hydrocarbons with one or more triple bonds are called alkynes and have the general formula CnH2n-2.
Naming alkenes and alkynes • Steps: • Identify the parent chain or ring that contains the multiple bond • Identify weather it is a double (-ene) or a triple (-yne) bond • Number the carbon atoms so that the multiple bond has the lowest number. Write this number before the suffix. For cyclic hydrocarbons, it is always between 1 and 2 and is not included. • Number and name the substituents the same as for alkanes. If the double/triple bond is in the middle of a chain, start numbering from the nearer end to the substituent group.
Naming alkenes and alkynes • draw the following: • 2-methylpent-1-ene • 4,5-dimethylhept-2-yne
Homework • Practice p 326, questions 1, 2 • Mini investigation: Isomers of pentene
Reactions of alkenes and alkynes • The double and triple bonds are functional groups, meaning that they affect the properties of the molecule. • Multiple bond molecules are more likely to undergo reactions because the bonds are less stable than single bonds.
Reactions of alkenes and alkynes • One common type of reaction of multiple bond molecules is addition reaction, in which two molecules react to form one. • In the case of alkenes and alkynes, the addition of hydrogen (hydrogenation)
Homework • Questions 2-8 p 328
Aromatic hydrocarbons • An aromatic is an unsaturated hydrocarbon that has a ring structure and a bonding arrangement that causes it to be chemically stable. • Benzene, C6H6, is a flat 6-carbon ring with one hydrogen bonded to each carbon. • Structural formulas often show benzene with alternating single and double bonds.
Aromatic hydrocarbons • In reality, all the bonds are equal, the bonds alternating between carbons. • These are called resonance structures. • A benzene ring is usually represented as an hexagon with a circle inside.
Naming aromatic compounds • The benzene ring is considered the parent molecule. • One substituent doesn’t get numbered. • More than one will be numbered using the first in alphabetical order and then going around in the direction that gives the smallest numbers.
