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.: 25096 or 374-8104 Email: [email protected]

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.

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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

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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

CnH2n+2

Alkenes

CnH2n

Alkynes

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.

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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.

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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

Means

an

only carbon-carbon single bonds

en

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.

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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.

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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).

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Some common functional groups are given in the table below. Common Functional Groups Functional Group Name

F, Cl, Br, or I

Example

Alkane

CH3CH2CH3 (propane)

Alkene Alkyne Alkyl halide Alcohol Ether Amine

CH3CH=CH2 (propene) CH3CCH (propyne) CH3Br (methyl bromide) CH3CH2OH (ethanol) CH3OCH3 (dimethyl ether) 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

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Example

Aldehyde

CH3CHO (acetaldehyde)

Ketone

CH3COCH3 (acetone)

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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 18. 3. 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 :

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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).

______________________________________________________________________________

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TYPICAL FRACTIONS OBTAINED BY DISTILLATION OF PETROLEUM. Boiling range of fraction (degrees Celsius) Below 20 degrees 20 – 60 degrees

Number of carbon atoms per Uses molecule C1 – C4 Natural gas, bottled gas, petrochemicals. C5 – C6 Petroleum ether, solvents

60 – 100 degrees

C6 – C7

Ligroin, solvents

40 – 200 degrees

C5 – C10

Straight – run Gasoline.

175 – 325 degrees

C12 – C18

Kerosene and Jet fuel.

250 – 400 degrees

C12 and higher

Gas oil, fuel oil and diesel oil

Nonvolatile liquids

C20 and higher

Nonvolatile solids

C20 and higher

Refined mineral oil, lubricating oil and grease. Paraffin wax, asphalt and tar

Reference: Tro, N. J (2004). Introductory Chemistry. (H. K. P., Ed.) USA: Pearson Education, Inc: Chapter 18.

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