The University of Trinidad and Tobago THE NATURE OF PROPERTIES OF INORGANIC AND ORGANIC COMPOUNDS

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1 The University of Trinidad and Tobago Course: CCCH 110D Course Instructors: Balram Mahabir Centre for Biomedical Engineering Point Lisas Campus. Ph: 642-8UTT (8888) ext.: or THE NATURE OF PROPERTIES OF INORGANIC AND ORGANIC COMPOUNDS ORGANIC VS. INORGANIC Organic compounds came from living things vs. Inorganic compounds came from the earth. Sugar from Cane vs. Salt from oceans Organic compounds can be easily decomposed vs. Inorganic Compounds are not easily decomposed. Burning of Sugar to form CO2 and H2O vs. Extremely high temperatures required to decompose salt. Organic compounds difficult to synthesize in the laboratory vs. inorganic compounds could be easily synthesized. Organic molecules usually are carbon-containing molecules vs. Inorganic molecules may not contain carbon. NaCl vs. CH4. WHY C? Carbon, with its 4 valence electrons, can form 4 covalent bonds When drawing organic compounds remember Carbon always form 4 bonds. Carbon, more than any other element can bond to itself to form chain, branched and ring structures. This versatility allows carbon to be the backbone of millions of different chemical compounds- just what is needed for life to exist. ALIPHATIC VS. AROMATIC HYDROCARBONS Hydrocarbons are organic molecules that consist exclusively, or primarily, of carbon and hydrogen atoms. There are two (2) types: Aliphatic compounds which consists of linear chains of carbon atoms and Aromatic compounds which consists of closed rings of carbon atoms. B. Mahabir CCCH110D 1

2 HYDROCARBONS Hydrocarbons are the simplest organic compounds. Containing only carbon and hydrogen, they can be straight-chain, branched chain, or cyclic molecules. Carbon tends to form four bonds in a tetrahedral geometry. Hydrocarbon derivatives are formed when there is a substitution of a functional group at one or more of these positions. AROMATIC HYDROCARBONS The building block of aromatic hydrocarbons is the benzene ring. The arrangement of atoms is shown below. The version in the center is often used to simplify diagrams of molecular structures. The three double bonds are not restricted to the positions shown but are free to pass around the ring. This is sometimes indicated by drawing the benzene ring as it is on the far right. Some examples of biological molecules that incorporate the benzene ring: the amino acids tyrosine and phenylalanine cholesterol and its various derivatives, such as the sex hormones o estrogens o testosterone the herbicide, 2,4-D B. Mahabir CCCH110D 2

3 ALIPHATIC HYDROCARBONS The simplest is methane, CH4. Next is ethane, C2H6. The fatty acids in fats are aliphatic hydrocarbons. If chain holds all the hydrogen atoms it can (i.e. 4 single bonds on all C atoms in the molecule), the molecule is said to be saturated. If two adjacent carbon atoms each lose a hydrogen atom, a double bond forms between them. Such a molecule is said to be unsaturated. Ethene is an example. H2C=CH2 NAMES AND FORMULAS OF SOME ORGANIC COMPOUNDS: Alkanes Alkenes Alkynes CnH2n+2 CnH2n CnH2n-2 Where n = Number of carbon atoms These formulas only apply to open-chain (non-cyclical) hydrocarbons. There are two skills that have to be developed in this area: You need to be able to translate the name of an organic compound into its structural formula. You need to be able to name a compound from its given formula. The first of these is more important (and also easier!) than the second. In an exam, if you can't write a formula for a given compound, you aren't going to know what the examiner is talking about and could lose lots of marks. However, you might only be asked to write a name for a given formula once in a whole exam - in which case you only risk 1 mark. B. Mahabir CCCH110D 3

4 So, we're going to look mainly at how you decode names and turn them into formulae. In the process you will also pick up tips about how to produce names yourself. In the early stages of an organic chemistry course people frequently get confused and daunted by the names because they try to do too much at once. Just go as far as the compounds you are interested in at the moment and ignore the rest. Come back to them as they arise during the natural flow of your course. CRACKING THE CODE A modern organic name is simply a code. Each part of the name gives you some useful information about the compound. For example, to understand the name 2-methylpropan-1-ol you need to take the name to pieces. The prop in the middle tells you how many carbon atoms there are in the longest chain (in this case, 3). The an which follows the "prop" tells you that there aren't any carbon-carbon double bonds. The other two parts of the name tell you about interesting things which are happening on the first and second carbon atom in the chain. Any name you are likely to come across can be broken up in this same way. COUNTING THE CARBON ATOMS You will need to remember the codes for the number of carbon atoms in a chain up to 6 carbons. There is no easy way around this - you have got to learn them. If you don't do this properly, you won't be able to name anything! code no of carbons meth 1 Eth 2 prop 3 but 4 pent 5 hex 6 Also Hept 7; Oct 8; Non 9; Dec 10 IUPAC Rule (International Union for Pure and Applied Chemistry) in this system, the longest continuous chain of carbon atoms called the Base Chain determines the base name of the compound. B. Mahabir CCCH110D 4

5 Groups of carbon atoms branching off the base chain are called alkyl groups and are names as substituents. A substituent is simply an atom or group of atoms that has been substituted for a Hydrogen atom on an organic compound. Common alkyl groups are shown below: Condensed Structural Formula Name - CH3 Methyl - CH2CH3 Ethyl - CH2CH2CH3 Propyl - CH2CH2CH2CH3 Butyl Refer to Table 18.3 TYPES OF CARBON-CARBON BONDS Whether or not the compound contains a carbon-carbon double bond is shown by the two letters immediately after the code for the chain length. code an en Means only carbon-carbon single bonds contains a carbon-carbon double bond For example, butane means four carbons in a chain with no double bond. Propene means three carbons in a chain with a double bond between two of the carbons. Alkyl groups Compounds like methane, CH4, and ethane, CH3CH3, are members of a family of compounds called alkanes. If you remove a hydrogen atom from one of these you get an alkyl group. For example: A methyl group is CH3. An ethyl group is CH3CH2. These groups must, of course, always be attached to something else. B. Mahabir CCCH110D 5

6 ISOMERS: What are isomers? Isomers are molecules that have the same molecular formula, but have a different arrangement of the atoms in space. That excludes any different arrangements which are simply due to the molecule rotating as a whole, or rotating about particular bonds. What is Structural Isomerism? Types of Structural Isomerism: 1. Chain isomerism These isomers arise because of the possibility of branching in carbon chains. For example, there are two isomers of butane, C4H10. In one of them, the carbon atoms lie in a "straight chain" whereas in the other the chain is branched.. Be careful not to draw "false" isomers which are just twisted versions of the original molecule. For example, this structure is just the straight chain version of butane rotated about the central carbon-carbon bond. 2. Position isomerism In position isomerism, the basic carbon skeleton remains unchanged, but important groups are moved around on that skeleton. For example, there are two structural isomers with the molecular formula C3H7Br. In one of them the bromine atom is on the end of the chain, whereas in the other it's attached in the middle. B. Mahabir CCCH110D 6

7 If you made a model, there is no way that you could twist one molecule to turn it into the other one. You would have to break the bromine off the end and re-attach it in the middle. At the same time, you would have to move a hydrogen from the middle to the end. Another similar example occurs in alcohols such as C4H9OH These are the only two possibilities provided you keep to a four carbon chain, but there is no reason why you should do that. You can easily have a mixture of chain isomerism and position isomerism - you aren't restricted to one or the other. So two other isomers of butanol are: 3. Functional group isomerism In this variety of structural isomerism, the isomers contain different functional groups - that is, they belong to different families of compounds (different homologous series). For example, a molecular formula C3H6O could be either propanal (an aldehyde) or propanone (a ketone). There are other possibilities as well for this same molecular formula - for example, you could have a carbon-carbon double bond (an alkene) and an -OH group (an alcohol) in the same molecule. Another common example is illustrated by the molecular formula C3H6O2. Amongst the several structural isomers of this are propanoic acid (a carboxylic acid) and methyl ethanoate (an ester). B. Mahabir CCCH110D 7

8 Some common functional groups are given in the table below. Common Functional Groups Functional Group Name Example Alkane CH3CH2CH3 (propane) Alkene CH3CH=CH2 (propene) Alkyne CH3CCH (propyne) F, Cl, Br, or I Alkyl halide CH3Br (methyl bromide) Alcohol CH3CH2OH (ethanol) Ether CH3OCH3 (dimethyl ether) Amine CH3NH2 (methyl amine) The C=O group plays a particularly important role in organic chemistry. This group is called a carbonyl and some of the functional groups based on a carbonyl are shown in the table below. Functional Groups That Contain a Carbonyl Functional Group Name Aldehyde Example CH3CHO (acetaldehyde) Ketone CH3COCH3 (acetone) B. Mahabir CCCH110D 8

9 Acyl chloride CH3COCl (acetyl chloride) Carboxylic acid CH3CO2H (acetic acid) Ester CH3CO2CH3 (methyl acetate) Amide CH3NH2 (acetamide) HYDROCARBON REACTIONS: 1. Combustion Reactions: Hydrocarbons (alkanes, alkenes and alkynes) all undergo Combustion. In a combustion reaction, the hydrocarbon reacts with oxygen to form carbon dioxide and water. Refer to examples in Chapter 18. Hydrocarbon combustion reactions are highly exothermic they emit large amounts of heat. This heat can be used to warm homes and buildings etc. 2. Substitution Reactions: Alkanes undergo substitution reactions, in which one or more hydrogen atoms on an alkane are replaced by one or more other atoms. For example halogen (F, Cl, Br, I) substitution. Refer to examples in Chapter Addition Reactions : Alkenes and Alkynes undergo addition reactions in which atoms add across the multiple bonds. For example the addition of chlorine converts the carbon carbon double bond into a single bond because each carbon atom now has a new bond to a chlorine atom. Alkenes and Alkynes can also add hydrogen in hydrogenation reactions in the presence of an appropriate catalyst. Refer to examples in Chapter 18. TO SUMMARIZE: All hydrocarbons undergo combustion reactions. Alkanes undergo substitution reactions. Alkenes and Alkynes undergo addition reactions. 4. Elimination : 5. Esterification : B. Mahabir CCCH110D 9

10 Alcohols react with carboxylic acids in the presence of catalytic amounts of a strong inorganic acid, such as H2SO4 or HCl, to give esters and water, a process called esterification. Eg acetic acid (ethanoic acid) and ethanol to give ethyl acetate and water (draw out structures) MONOMERS, POLYMERS AND POLYMERIZATION. Polymers are long chainlike molecules composed of repeating units. The individual repeating units are called monomers. Naturally occurring polymers include starches, proteins and Deoxyribonucleic Acid (DNA) while Synthetic polymers compose many frequently-encountered plastic products such as PVC tubing, Styrofoam products, nylon and plexiglass. Addition polymer polymer in which the monomers simply link together without the elimination of any atoms (e.g. polyethylene), Condensation polymer polymer that eliminate an atom or a small group of atoms during polymerization. HYDROCARBON CRACKING VS. HYDROCARBON REFORMING Hydrocarbon Cracking : Breaking an alkane down into smaller fragments is known as Cracking. When a mixture of alkanes from the gas oil (C12 and higher) fraction are heated at very high temperatures ( approx 500 degrees Celsius) in the presence of a variety of catalysts, the molecules break apart and rearrange to smaller, more highly branched alkanes containing 5 to 10 carbons. This process is called catalytic cracking. Cracking can also be done in the absence of a catalyst called thermal cracking but in this process the products tend to have unbranched chains, and alkanes with unbranched chains have a very low octane rating. Such processes are important in the oil refining industry for the production of gasoline and other liquid fuels from petroleum. Reforming : Another process converts alkanes into aromatic hydrocarbons with approx. the same number of carbon atoms. The aromatics are highly efficient fuels and are used as feedstocks for the chemical industry. Because the process reforms a new hydrocarbon from an old one, it is referred to as Reforming. An example of reforming is the conversion of heptane into methylbenzene (toluene). B. Mahabir CCCH110D 10

11 TYPICAL FRACTIONS OBTAINED BY DISTILLATION OF PETROLEUM. Boiling range of fraction Number of carbon atoms per Uses (degrees Celsius) molecule Below 20 degrees C1 C4 Natural gas, bottled gas, petrochemicals degrees C5 C6 Petroleum ether, solvents degrees C6 C7 Ligroin, solvents degrees C5 C10 Straight run Gasoline degrees C12 C18 Kerosene and Jet fuel degrees C12 and higher Gas oil, fuel oil and diesel oil Nonvolatile liquids C20 and higher Refined mineral oil, lubricating oil and grease. Nonvolatile solids C20 and higher Paraffin wax, asphalt and tar Reference: Tro, N. J (2004). Introductory Chemistry. (H. K. P., Ed.) USA: Pearson Education, Inc: Chapter 18. B. Mahabir CCCH110D 11