Chemistry 11. Unit 10 Organic Chemistry Part IV Functional Groups

Transcription

1 Chemistry 11 Unit 10 Organic Chemistry Part IV Functional Groups

2 2 1. Introduction to functional groups So far we have introduced a big family of compounds called hydrocarbons in which all members are made of carbon and hydrogen. These compounds show a variety of structural features such as orders of bonds, ring conformation, and cis-trans isomerism. From chemistry perspective, however, the usage and properties of these organic compounds are rather limited. Fortunately, pure hydrocarbons (i.e., alkanes, alkenes, alkynes and aromatics) only make up a small portion of the realm of organic chemistry.

3 3 The majority of organic compounds consists of those containing not only carbon and hydrogen, but also other elements (called heteroatoms) such as oxygen, nitrogen, sulfur and halogens. It is observed that some specific groups of atoms are usually present in compounds and they give the compounds specific properties and reactivity. These groups of atoms are called functional groups. Functional groups: defined as a specific atom or group of atoms in a molecule to which specific physical and chemical properties of the molecule are attributed to.

4 4 Many functional groups have been identified in organic chemistry, and each one has a unique structure and specific chemical reactivity. In chemistry 11, we would focus on the functional groups which contain one or more oxygen atoms, plus a number of functional groups having a nitrogen atom.

5 5 The naming of compounds with functional groups is done according to the following rules: (1) Identify the longest continuous carbon chain containing the functional group. This will determine the parent name. (2) Change the ending of the parent name to the ending specific to the functional group. (3) Number the carbon atoms starting from the end closest to the functional group, and label side chain accordingly. (4) Name side chains in the alphabetical order.

6 6 2. Alcohol When a hydrogen atom in an hydrocarbon is replaced by a OH group, the compound is converted to an alcohol. The functional group OH is also called a hydroxyl group. Alcohols have the general formula of C n H 2n+1 OH.

7 7 The naming of alcohols is similar to branched alkanes except that the ending e is replaced by ol. For example: 4-carbon chain OH group at carbon #2 Name: 2-butanol 6-carbon chain OH group on carbon #2 Methyl group on carbon #5 Name: 5-methyl-2-hexanol

8 8 Practice: Name the following alcohols.

9 9 When the OH group is attached to a benzene ring, the resulting compound is called a phenol. The naming of phenol compounds is similar to substituted benzenes except that the carbon on which OH group is attached is labeled carbon 1. Phenol 2-nitrophenol 4-bromophenol

10 10 Some properties of alcohols (1) The boiling point of an alcohol is higher than the corresponding alkane with the same length of the carbon chain. The reason is due to the formation of hydrogen bonds between the alcohol molecules.

11 11 (2) All alcohols are poisonous!

12 12 (3) The solubility of an alcohol depends on the residue attached to the OH group. Despite the polar nature of OH, the non-polar hydrocarbon chain in alcohol will dominate the molecular polarity and make the alcohol insoluble in water if it gets large.

13 13 3. Ether When an oxygen atom is inserted between two carbon atoms in a hydrocarbon molecules, an ether is formed. Ether shares the general molecular formula of C n H 2n+2 O, which is similar to that for alcohols. Because of the different connectivity, ethers behave in very different ways from alcohols. In general, ethers are non-polar and relatively unreactive. The latter property causes ethers to be good organic solvents in chemical synthesis.

14 14 The naming rule for ethers is straightforward: Name the two substituents on the linking O atom separately according to the alphabetical order, and then follow by ether. Dimethyl ether Ethyl methyl ether Ethyl propyl ether Butyl propyl ether

15 15 If additional side chains are present on the two substituents, these groups will be named in the same way as they are named for substituted hydrocarbons, with the numbering starting from the carbon bonded to the O atom. For example, the following compound is named ethyl 2-chloropropyl ether. Ethyl substituent Propyl substituent Chloro group at second carbon of the propyl substituent

16 16 The naming method just introduced is commonly used in literature. There exists another more updated and systematic way of naming ethers. In this approach, the longer group attached to the O atom in ether is considered as the parent compound, and the shorter one with the O atom is considered as a functional group called alkoxy. Parental chain: ethane Function group: methoxy This compound is therefore called methoxyethane.

17 17 Example: Give systematic names to the following compounds.

18 18 Some properties and applications of ethers: (1) Ethers are volatile and flammable! (2) Ethers are good organic solvents. (3) Low ethers can be used as anaesthetics, refrigerants and perfumery. (4) Some (e.g. anisole) are essential oils and artificial flavors.

19 19 4. Aldehyde When carbon and oxygen atoms are connected by a double bond, a carbonyl group is formed. There are a vast number of compounds possessing the carbonyl functional group. Depending on the substituents attached to the carbonyl, many types of compounds can be generated such as aldehyde, ketone, acid, ester, and amide.

20 20 When the carbonyl is bonded to a hydrogen on one side, and alkyl group on the other side, an aldehyde is formed. For example:

21 21 To name an aldehyde: (1) The longest chain containing the carbonyl group is considered as the parent compound. (2) The carbonyl carbon is always the #1 position. (3) Label other side chains accordingly. (4) Finish the name with an ending al. The longest chain has 3 carbons; therefore the parent compound is propane No other side chain is present The name of the compound is propanal.

22 22 The longest chain has 5 carbons; hence the parent compound is pentane. One methyl on C2 and one ethyl on C3. The name of the compound is 3- ethyl-2-methylpentanal The longest chain has 8 carbons; hence the parent compound is octane. One chloro group on C3, one methyl on C4 and one hydroxyl on C6. The name of the compound is 3- chloro-6-hydroxy-4-methyloctanal

23 23 Practice: Name the following compounds.

24 24 Some interesting facts about aldehydes: (1) Small aldehydes are soluble in water, while the heavier ones are not. (2) Aldehydes are volatile with pungent smell. Some of them can be found in the essential oil extracts of plants such as cinnamaldehyde (in cinnamon), cilantro (in Chinese parsley) and vanillin (in vanilla bean) cinnamon Vanilla bean

25 25 (3) The smallest aldehyde, methanal or formaldehyde, is an irritating, water-soluble gas which shows a broad range of applications such as the precursors to synthesize resins and plastics, the disinfectant that kills bacteria and parasites, and the formalin solution which preserves cells and tissues.

26 26 (4) Aldehydes participate in the Tollen s test (also known as silver mirror test) in which aldehyde reduces Ag + ion from silver nitrate to metallic silver which deposits on the inner surface of the reaction container.

27 27 5. Ketone If the carbonyl carbon is attached to two carbon atoms (i.e., two alkyl groups), the functional group will become a ketone. Because of this constraint, ketone can never appear at the terminal positions of a carbon chain. The two groups attached to ketone could be purely alkyls, substituted alkyls, or aromatic.

28 28 To name a ketone, the following rules are used. (1) The longest continuous chain containing the ketone group is considered as the parent compound. The ending e is replaced by one. (2) The chain carbons are numbered in such a way that the ketone group has the smallest number possible. This number has to be indicated as a prefix in the name. (3) Other side chains or substituents are labelled according to the numbering of the carbon chain.

29 29 Example: Name the following compounds. The longest chain has 4 carbon atoms; so the parent compound is butane The ketone group is at C2 The name of the compound is 2- butanone The longest chain has 6 carbon atoms; so the parent compound is hexane The ketone is at C3 A methyl group on C5 The name of the compound is 5-methyl- 3-hexanone

30 30 If there are two or more ketone groups in a compound, they should be labeled separately. For example: The longest chain has 9 carbon atoms; so the parent compound is nonane. Counting from the left, the ketone groups are at C3 and C6 respectively. Cl at C2, propyl at C5 and Br at C7 The name: 7-bromo-2-chloro-5-propyl-3,6-nonanedione

31 31 Some applications of ketones: (1) They are widely used as solvents in organic chemistry. For example, acetone (propanone) was produced at a scale of 6.7 million tonnes per year in (2) Ketones are also used as precursors to polymer synthesis. (3) Acetone is used for chemical peeling and nail polish removers in cosmetics, or as food additives.

32 32 6. Carboxylic acid When a carbonyl exists at a terminal position and is attached on one side to a hydroxyl group, the functional group is called a carboxylic acid. Carboxylic acids have the general formula C n H 2n+1 COOH.

33 33 The naming rules for carboxylic acids are similar to those for aldehydes: (1) The longest chain containing the carboxylic acid is the parent compound. The carboxylic carbon is labeled 1. (2) All other side chains are named based on the positions of the carbons on which they are attached. Follow the alphabetical order. (3) The ending of the parent compound e is replaced by oic acid.

34 34 Example: Name the following compounds. The longest chain has 4 carbon atoms; so the parent is butane. The name of the compound is butanoic acid. The longest chain contains 7 carbon atoms; so the parent is heptane. Chloro at C2, ethyl at C3, phenyl at C5 The name of the compound is 2- chloro-3-ethyl-5-phenyl heptanoic acid.

35 35 Practice: Name the following compound.

36 36 Some interesting facts of carboxylic acids: (1) The melting points and boiling points of carboxylic acids are generally high because of the formation of hydrogen bonds.

37 37 They are weak acids. Many of them can be found in nature. Erucic acid (found in canola oil) Citric acid (found in lemon) Oxalic acid (found in spinach)

38 38

39 39 7. Esters Ester is a functional group consisting of a carbonyl and an oxygen attached to the carbon. Symbolically, it is a COO- group that joins two hydrocarbon chains together. Simple esters have a general formula: C n H 2n+2 COO For example:

40 40 Naming of esters is a little bit different from that for other functional groups. Since each ester consists of two hydrocarbon groups as show below: we have to label them one by one. The R1 group is named as a typical substituent, and the R2 group plus the carbonyl C form the parent compound. Since acid group always appears at the terminal position, the carbonyl C is numbered C1.

41 41 When you need to name an ester, change the ending of the parent compound e by oate. For example: The R1 group is propyl The R2 group has 1 carbon; therefore the parent compound is ethane The name of the compound is propyl ethanoate The R1 group is ethyl The R2 group has 5 carbons; therefore the parent is pentane Ethyl at C2 and Cl at C4 The name of the compound is ethyl 4-chloro-2-ethylpentanoate

42 42 Practice: Name the following compound.

43 43 Some properties of esters: (1) Esters have very pleasant smells and they are responsible for the odors of many fruits and foods.

44 44 (2) Ester is formed in the process called esterification in which a carboxylic acid reacts with an alcohol to produce an ester and water. RCOOH + R OH RCOOR + H 2 O In the presence of acid or base, the esterification can be reversed. The reaction, called hydrolysis, breaks an ester into the corresponding acid and alcohol. Note, however, that the process is reversible in acidic medium but irreversible if a base is present.

45 45 (3) The basic hydrolysis of ester is also called saponification which is the process of making soap from ester. When triglycerides (which are esters of fatty acids) in fat or oil react with NaOH or KOH, they are converted to soap and alcohol.

46 46 8. Amide Amide derives from a carboxylic acid in which its OH group is replaced by an amino group NH 2. Therefore, it has a general formula: C n H 2n+1 CONH 2. Some representative amides are shown below.

47 47 The nitrogen in simple amide is bonded to a carbonyl and two hydrogen atoms. The two hydrogen atoms can be substituted by other alkyl groups, and they can either identical or different. Depending on the substituents on the N atom, amides can be classified into three types: Type of amide Structural feature Primary -CONH 2 Secondary Tertiary -CONHR -CONRR

48 48 The naming rules for amides: (1) Identify the longest continuous carbon chain containing the carbonyl group. This chain will be the parent compound. Since amide group is always at the end of the chain, it is not necessary to label its position. (2) Other substituents are labelled according to their positions on the chain. (3) For secondary and tertiary amides, the substituents on N are labelled with the position N. (4) All side chains appear in the compound name following the alphabetical order. The ending of the parent is changed from e to amide.

49 49 Example: Name the following compounds. The longest chain has 5 carbon atoms; so the parent is pentane. One methyl group on C3. The name is 3-methylpentanamide. The longest chain has 4 carbon atoms; so the parent is butane. One chloro on C3 and one chloro on C4. An ethyl group on N. The name is 3,4-dichloro-Nethylbutanamide.

50 50 Practice: Name the following compound.

51 51 Some properties of amides: (1) Amide is a materials commonly used in making synthetic polymers such as nylon (6,6). (2) Amides and related compounds are potent drugs and pharmaceuticals. Penicillin LSD

52 52 (3) Amide forms the backbone of proteins called peptide linkage, and the availability of hydrogen bond formation by amide groups allows the folding of protein molecules in three dimensions. Glycine Alanine Valine Serine

53 53 9. Amine Another common functional group that contains N atom is called amine. Amine refers to molecules having a NH 2 group. This group is not attached to a carbonyl group. Simple amines share a general formula of C n H 2n+1 NH 2. Simply speaking, an amine can be considered as an alkane with one of its hydrogen replaced by an amino group. Amines can be classified as primary, secondary or tertiary depending upon how many substituents are attached to the N atom.

54 54 There are 2 ways of naming amines. (a) The systematic way: (1) Find the longest continuous chain containing NH 2 group and treat it as the parent. (2) Label other side chains as usual. (3) Change the ending, -e, of the parent to amine. (4) Specify the position of NH 2. 1-propanamine 2-pentanamine

55 55 (b) The common way: (1) Choose the longest chain and treat it as the parent compound. (2) Label side chains as usual. (3) Label NH 2 group as a side chain and specify its position. The longest chain has 8 carbon atoms; so the parent is octane. Ketone group at C3, and amino group at C5. The name is 5-amino-3-octanone.

56 56 Practice: Name the following compounds.

57 57 Some properties of amines: (1) They are organic bases commonly used in organic synthesis. (2) Usually amines have relatively high melting points and boiling points because of the presence of hydrogen bonds. (3) Amines are useful in making drugs, dyes and gas treatment in oil refinery. (4) Amines have unpleasant smell in general (like fish). Heroin

58 Multi-functional group molecules While most of the examples mentioned previously contain only one or two functional groups, in reality the majority of the organic compounds found in nature possesses many functional groups. The naming of these compounds is very complicated and extremely tedious. For example: Vitamin B2 IUPAC name: 7,8-Dimethyl-10- [(2S,3S,4R)-2,3,4,5- tetrahydroxypentyl]benzo[g]pte ridine-2,4-dione

59 59 An extreme example: Paclitaxel a chemotherapy medication that treats a number of cancers such as ovarian cancer, breast cancer and lung cancer. The IUPAC name: (2α,4α,5β,7β,10β,13α)-4,10- Bis(acetyloxy)-13-{[(2R,3S)- 3-(benzoylamino)-2- hydroxy-3- phenylpropanoyl]oxy}-1,7- dihydroxy-9-oxo-5,20- epoxytax-11-en-2-yl benzoate

60 60 If there is more than one functional group present in a molecule, we will have to decide which one should be chosen as the parent compound according to the hierarchical order.

61 61 Let s try some examples. (1) Vanillin: the compound responsible for the aroma and flavor of vanilla.

62 62 (2) Capsaicin: An active compound in chilli peppers. It is irritating to human, causing a feeling of burning in any tissue when in direct contact.

63 63 In Chemistry 11, we won t go deep into the organic nomenclatures. Despite this, we should be equipped with the skills of identifying various functional groups in any given compound, as it serves as the first step of the designed synthesis of an organic compound of desired physical, chemical or biological interest. Have a close look into the following compounds, and try to identify as many functional groups as you can.

64 64 (1) Ciprofloxacin: An antibiotic for treating bacterial infections such as bone and joint infections.

65 65 (2) Morphine: A pain medication that interacts directly with CNS to reduce the feeling of pain.

66 66 (3) Homoharringtonine: A pharmaceutical drug that treats chronical myeloid leukemia (CML).

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