Carbon Compounds

1. Carbon Compounds John Leaver

2. Organic Chemistry • The vast majority of the compounds of the element carbon are called ‘Organic Compounds’ and their study is known as ‘Organic Chemistry’. • Their large number is a consequence of the ability of carbon atoms to link together to form ‘chains’ and ‘rings’

3. Why ‘organic’ compounds? • These substances are frequently found in living, or once living, matter – hence the name organic. • It was once thought that they could only be created by ‘organic’ processes (i.e. from living material).

4. Note on Nomenclature • The naming of organic compounds is an extensive subject with its own literature. • This presentation is concerned more with giving an impression of the variety of organic compounds • No attempt will be made in this session to teach the rules for naming organic compounds in a systematic way • Although you are likely to ‘pick up’ some aspects of the topic

5. Hydrocarbons • The least complicated organic compounds, with respect to their chemical behaviour, are those that contain only carbon and hydrogen atoms. These are called ‘hydrocarbons’. • There are several classes of hydrocarbon – they differ with respect to the bonding present between carbon atoms.

6. Alkanes (old name ‘paraffins’) • In alkanes there are only single bonds between carbon atoms. • Each carbon atom is able to form four bonds in total • In alkanes all ‘spare’ bonds are to hydrogen atoms

7. Alkanes – Example: Butane A chain of Four carbon atoms joined by single bonds All remaining bonds have hydrogen atoms attached, each carbon atom having four bonds in total Butane C4H10 or CH3CH2CH2CH3 is a gas used as a fuel

8. Note on the Representation of Organic Molecules • It is important to be aware that in all but the most introductory of text books it is usual to assume the presence of most of the carbon and hydrogen atoms when depicting organic molecules • Hence butane is more commonly shown as:

9. Representation of molecules - 2 You may also see 3D representations of molecules in ‘ball and stick’ form:

10. Representation of molecules - 3 • You may also encounter ‘space filling’ views that give an indication of the ‘surface’ of the molecule

11. General formula for Alkanes • The molecular formulae of the series of straight chain alkanes may be represented by the following formula: CnH2n+2 • The first fifteen are named on the next slide (notice that after the first four the name tells you how many carbon atoms are present).

12. Names of Alkanes • Nonane (n=9) • Decane (n=10) • Undecane (n=11) • Dodecane (n=12) • Tridecane (n=13) • Tetradecane (n=14) • Pentadecane (n=15) • Methane (n=1) • Ethane (n=2) • Propane (n=3) • Butane (n=4) • Pentane (n=5) • Hexane (n=6) • Heptane (n=7) • Octane (n=8) As chain length increases physical properties change: e.g. at room temp n=(1-4) gases, n=(5-16) liquids, n>16 solids

13. More complex alkane chains • It is also possible to have branched alkane chains such as: 8-butyl-5,11-diethyl- pentadecane This should help to indicate the enormous possibilities with respect to both size and complexity for alkane molecules

14. Alkenes (old name ‘olefins’) • Alkenes contain at least one example of a double bond between carbon atoms. • As with alkanes, the remaining (non Carbon to Carbon) bonds are to hydrogen atoms. • Alkenes are said to be ‘unsaturated’ i.e. there is scope for the addition of other atoms or radicals. • They are therefore more chemically reactive than the ‘saturated’ alkanes.

15. Alkenes – Example: But-2-ene The ‘2’ indicates the position of the bond NB Alkenes have a higher percentage of carbon than do alkanes – they therefore burn with a smokier flame Double bond

16. But-2-ene: other representations The double bond on the ball and stick structure is represented by being shorter than the single bonds (more electrons are involved in forming the bond so the carbon atoms are pulled closer together)

17. More complex alkenes • Obviously hydrocarbon molecules may contain more than one double bond • They are then ‘poly-unsaturated’:

18. Alkynes (old name ‘acetylenes’) • Alkynes are hydrocarbons containing at least one ‘triple bond’ between carbon atoms. They are rather reactive compounds. • The simplest example is ethyne:

19. Cyclic hydrocarbons • As well as chains of carbon atoms it is also possible to have rings • These are called cyclic compounds • The three sorts of hydrocarbon we have seen so far can exist in rings and these are called cycloalkanes, cycloalkenes and cycloalkynes respectively (the latter are not commonly encountered)

20. Cycloalkanes and Cycloalkenes • Some examples: Cyclohexane Methylcyclopropane Cyclopenta-1,3-diene

21. Aromatic compounds • It might be supposed that a compound with this structure would be named cyclohexa-1,3,5-triene and would behave as though it had alternate single and double bonds • However, when a ring of six carbon atoms, each attached to one hydrogen atom is made, it behaves as though all the carbon-carbon bonds are equivalent

22. Benzene • In such a ring structure as on the previous slide the bonding electrons are able to spread around the ring (or ‘delocalise’) and the C6H6 ring is actually called benzene • Compounds containing this structure are called ‘aromatic’ compounds

23. Representing benzene • Sometimes it is convenient to represent benzene rings with alternate single and double bonds, like this: • Alternatively they may also be represented by a hexagon containing a circle to indicate the delocalised electrons:

24. Other aromatic hydrocarbons • It is possible for several benzene rings to join together to make larger molecules, such as: anthracene phenanthrene

25. Heterocyclic Compounds • It is also possible for one or more of the carbon atoms in a ring system to be replaced by another sort of atom (for example oxygen or nitrogen) • Such compounds are called ‘heterocyclic’ • Many important biological molecules are heterocyclic (e.g. see sugars later)

26. Example of a Heterocyclic Compound Deoxy-ribose

27. Functional Groups • Organic chemicals often display characteristic properties as a consequence of the functional groups that they contain • Functional groups are small groups of atoms that allow the molecule to react with other molecules in specific ways. • Some examples will be found on the following few slides

28. Some Important Functional Groups

29. Functional Groups in more detail • In the next few slides we will look at each of the functional groups from the table • In particular we will consider: • Alternative names • Properties • Biological examples

30. Alcohols – the hydroxy group, -OH • Alcohols contain the hydroxy group, OH. • E.g. CH3CH2OH ethanol or ethyl alcohol (a familiar compound to many) Phenol cyclohexanol The aromatic alcohols are known as phenols

31. Alcohols - 2 • Alcohols sometimes have a pleasant odour although the longer chain alcohols can have a rather ‘sickly’ smell. Aromatic alcohols have a sharper smell. • Many alcohols are flammable. • Some liquid alcohols (those with shorter chains and smaller rings) are also used as solvents and are miscible to some extent with water.

32. Alcohols - 3 • The hydroxy group is common in biological molecules and pharmaceutical compounds: Dopamine (a neural transmitter and sympathomimetic drug) -D–glucose (a sugar)

33. Aldehydes -CHO • The simplest aldehyde is ‘formaldehyde’HCHO (proper name, methanal,) used to preserve biological specimens. • The aldehyde structure contains a ‘carbonyl’ group (C=O) Ethanal (old name, Acetaldehyde)

34. Aldehydes - 2 • Aldehydes are often rather pungent. Benzaldehyde – is the constituent of almonds that gives them their characteristic ‘marzipan’ smell

35. Aldehydes - 3 • The carbonyl group in aldehydes makes them somewhat reactive • Under the right conditions aldehydes may be ‘reduced’ to alcohols or ‘oxidized’ to carboxylic acids

36. Aldehydes - 4 • Examples of the aldehyde group in biological/medicinal compounds Cinnamaldehyde Vanillin

37. Amines – the amino group NH2 • Simple examples are: CH3NH2 methylamine or aminomethane aminobenzene or aniline cyclohexylamine or aminocyclohexane

38. Amines - 2 • Amines often have a ‘fishy’ odour and are associated with decomposition: “Putrescine” (butane-1,4-diamine) “Cadaverine” (pentane-1,5-diamine) Both compounds are found in decomposing corpses!

39. Amines - 3 • Examples of the amino group in biological/medicinal compounds Adenine – one of the five nucleic acid bases Amphetamine – a CNS stimulant etc

40. Carboxylic acids -COOH • Common example: Ethanoic acid (CH3COOH) – commonly known as ‘acetic acid’. The active ingredient of vinegar. It forms when ethanol is oxidised, causing the vinegary taste of stale wine.

41. Carboxylic acids - 2 • The smaller carboxylic acids tend to be pungent, corrosive liquids: ‘Formic acid’ or methanoic acid (HCOOH) – a corrosive substance sprayed by ants ‘Butyric acid’ or butanoic acid occurs in rancid butter and stale sweat

42. Carboxylic acids - 3 • Biological/medicinal examples of compounds containing -COOH Citric acid – gives citrus fruits their sharp flavour Kainic acid – an anthelmintic

43. Esters –COOC- • Esters form when carboxylic acids react with alcohols. They often have fruity odours: For example: Pineapples smell of ethyl propanoate CH3CH2COOCH2CH3 and other esters ‘Ester linkage’

44. Esters - 2 • Biological/medicinal examples benzocaine – a local anaesthetic Dimethy phthalate (‘DIMP’) an insect repellent

45. Ethers: -O- • Ethers contain carbon atoms linked by an oxygen atom • The oxygen atom may link chains or rings, or be within a ring (cyclic ethers). diethyl ether or ethoxyethane commonly just called ‘ether’ A ‘crown’ ether – this one is 18-crown-6

46. Ethers - 2 • The smaller ethers are liquids with low boiling points, flammable and immiscible with water • They are used as solvents • Ethers are generally rather un-reactive • Diethyl ether has been used as an anaesthetic • Larger ethers with many ether links may be water miscible

47. Ethers - 3 • Biological/medicinal examples Cineole (1,3,3-trimethyl-2- oxabicyclo[2.2.2]octane) a constituent of eucalyptus oil Myristicin – a psychotropic constituent of Nutmeg

48. Halogen compounds: -X • The halogens fluorine (F), chlorine (Cl), bromine (Br) and iodine (I) may bind to carbon atoms in organic compounds • The properties of these compounds are rather diverse as a consequence of the differences between the chemical properties of the halogens • Some examples will be found on the next slide

49. Halogen compounds - 2 trichloromethane or ‘chloroform’ a solvent and anaesthetic ‘Circladin’ an anticoagulant ‘Capacin, a thyroid inhibitor Myelotrast a radio-opaque agent

50. Ketones: C=O • Ketones contain a carbonyl group, C=O • Smaller ketone molecules are liquids and are often good solvents for other organic compounds • Acetone (propan-2-one) is a commonly used solvent: