ORGANIC CHEMISTRY

1. ORGANIC CHEMISTRY http://www.foresight.org/conferences/MNT7/Papers/Hersam/Fig3.gif

2. ORGANIC MOLECULES General information - Organic chemistry refers to the chemistry of CARBON compounds - The carbon atom can form a maximum of 4 covalent bonds - It can bond to other carbon atoms, to form single, double or triple bonds - Can bond to other carbon atoms to form long chains, branches or ring structures - Can bond with other atoms (eg. Hydrogen, oxygen. Nitrogen, halogens, etc.) Functional groups - Organic molecules can be separated into families according to their chemical and physical properties - The structural property that enables us to classify the compound according to its reactivity is known as the FUNCTIONAL GROUP - The functional group is an atom or group of atoms that are characteristic of a group of compounds that form a homologous series and are responsible for the specific property of that group Homologous series - Organic molecules corresponding to the same family form a homologous series - Compounds in a homologous series have the same functional group and can be described using the same general formula. (Eg. Alkanes CnH2n=+2)

3. Representing organic molecules - Different types of formula can be used to represent organic molecules - Molecular formula (indicates the amount of atoms in the molecule) C4H10 (Butane) - Condensed structural formula (shows how the atoms are bonded – but no bonds) CH3CH2CH2CH3 (Butane) - Structural formula (Shows all atoms including their associated bonds) • Line structure (lines represent bonds, ends of lines represent carbon atoms) • Three dimensional formula (wedges to indicate bonds into and out of page)

4. Classification of organic compounds • Isomers • - Molecules that have the same molecular formula, but different structures • - Only consider structural isomers (though you get geometric and stereo isomers) • - Example: C4H10

5. Alkanes • Saturated hydrocarbons (only contain single bonded carbon atoms) • Homologous series: Cn H2n+2 • Naming Alkanes… • IUPAC system of naming… • Involves the use of a prefix, root and suffix • PREFIX : Explains where, and which functional groups are present • ROOT : Number of carbon atoms • SUFFIX : Family or homologous series - The following are used to indicate the number of carbons present in the molecule:

6. Some molecules contain branches (where a hydrogen has been replaced with carbon chains) – The carbon chain is called an ALKYL group • These are represented with an R- in the structural formula • These alkyl groups are named as follows… Procedure for naming: 1) Find the LONGEST continuous carbon chain in the molecule (becomes root) 2) Identify the attached alkyl groups 3) To indicate the positions of the branches, number the carbon atoms in the longest chain, starting from the side closest to a branch! 4) To write down the name, start by writing down the position and name of all the attached groups in alphabetical order. (if there is more than 1 of a particular alkyl group, use the prefixes: Mono, di, tri and tetra to indicate the number of groups Note: the name is written as 1 WORD, with numbers and words separated by dashes (-)

7. Cycloalkanes • - Carbon atoms can bond to each other to form rings (consider cyclohexane C6H12) • Homologous series: Cn H2n • Naming Cycloalkanes… • If substituents are present, the Carbon atoms in the ring are numbered in such a way • that the substituent is on the lowest number • 2) Arrange the substituents in alphabetical order and use di, tri and tetra to indicate the • number of like substituents • 3) If the ring contains 2 different alkyl groups, number the C atoms in the ring so that • the alkyl group that is first in the alphabet receives the lowest number Note: - Alkanes are our most import fuels (fossil fuels) - Combustion of alkanes (oxidation) is HIGHLY EXOTHERMIC and produces carbon dioxide and water as products (along with energy) ALKANE + O2H2O + O2 + ENERGY!!! ∆H < 0

8. Structural and physical properties of alkanes • 1) Phases (at room temperature) • - C1 to C4 alkanes gases • - C5 to C17 alkanes liquids • - C18+ solids (plastic – PET) • - The intermolecular forces between alkane molecules increases as the • molecule increases in size (increased molecular mass) • 2) Densities • - less dense than water • - density inceases as size increases (also explained by intermolecular forces) • 3) Volatility and vapour pressure • - volatility is the measure at which a liquid changes to a vapour • - Alkane volatility decreases as size increases (stronger forces, less volatile) • - Vapour pressure refers to the pressure caused by the vapour formed • - Thus less volatility, less vapour pressure • 4) Viscosity • - viscosity is refers to the degree of fluidity (or flow) of a liquid • - Viscosity increases with intermolecular force strength

9. 5) Solubility - The ability to dissolve in another substance (solvent) - Alkanes are non-polar, thus they will dissolve in non-polar solvents (organic solvents and not in a polar solvent such as water 6) Melting and boiling points - Consider the table of melting and boiling points - van der waals forces (intermolecular forces) increases as the molecule size increases. The stronger the forces, the more energy is required to break the forces, resulting in a higher boiling point - Similarily with melting points, as the size of the molecule increases so does the melting point - It can be seen in the graph that the increase is not smooth (as is the case with boiling). This is because alkanes with an even number of carbon atoms pack together very well in the solid phase, and thus more energy is required to overcome the intermolecular forces

10. Alkenes • Unsaturated hydrocarbons (covalent double bonds between carbon atoms) • The double bond is a centre of high reactivity (high electron density) • Homologous series: Cn H2n • The simplest alkene is ethene… • Procedure for naming: • Find the longest chain containing the double bond. (This becomes the root) • Add the suffix “ene” to the root • Number the chain starting from the end closest to the double bond • The position of the double bond is indicated by the number on the first carbon atom • of the double bond • 5) When the root chain contains branched substituents, the same rules used for naming • alkanes is followed • Note: The position of the double bond can be indicated in two ways… 3,3 – dimethyl – 1 – butene OR 3,3 – dimethylbut – 1 – ene

11. Cycloalkenes • - The number of carbon atoms in the ring determines the root • - Number the ring in such a way so that the double bond is between C1 and C2 • - As well as allowing for the lowest numbers on the substituents • - If there is only one double bond present, The carbon on which it starts doesn’t have • to be indicated in the name (as it will always start on C1) • - If there are 2 double bonds, the molecule is known as a DIENE • In this situation, the suffix “diene” is used, and the position of the double bonds • must be indicated • - When there are two sets of double bonds connected to a single carbon atom, the • molecule is known as a CUMULATED DIENE Note: Consider the following molecule… • This is an example of a compound with CONJUGATED double bonds • A conjugated double bonds system is a system where single and double bonds follow one another in a carbon chain • These are very interesting molecules when it comes to reactivity because the electrons in the double bonds are DELOCALISED over the whole molecule!

12. Structural and physical properties of alkenes • Phases (at room temperature) • - C2 to C4 gases • - C5 to C15 liquids • - C16+ solids (plastic – PET) • Alkenes are NON – POLAR • - Thus weak van der waals forces exist between molecules • - alkenes insoluble in water (polar) • - Soluble in organic solvents (non-polar) • Melting and boiling points • - Consider the table of melting and boiling points • - These can be explained by the van der waals forces • - strength of forces increases as the molecule size increases

13. Alkynes • - Unsaturated hydrocarbons (covalent TRIPLE bonds between carbon atoms) • - The triple bond is a centre of high reactivity (high electron density) • - Homologous series: CnH2n-2 • Procedure for naming: • The same rules apply as for the naming of alkenes, but the suffix –yne is used • Structural and physical properties of alkynes • - The phase of the alkynes also depends on the molecular mass (size) of the molecule • Phases (at room temperature) • - C2 to C4 gases • - C5 to C17 liquids • - C18+ solids (plastic – PET) • Alkynes are NON – POLAR • - Thus weak van der waals forces exist between molecules • - alkynes are insoluble in water (polar), but Soluble in organic solvents (non-polar) • - Alkynes are less dense than water • Melting and boiling points • - Can be explained by the van der waals forces • - strength of forces increases as the molecule size increases

14. Structural and physical properties of alkynes • - Consider the two types of van der waals forces… • - Van der waals dispersion (or London) forces • - When 2 NON-polar molecules approach each other, attraction as well as repulsion, • between the nuclei can cause an unequal distribution of charge • - This causes, TEMPORARY dipoles to be produced • - These temporary dipoles induce temporary dipoles in adjacent molecules • - This results in a weak force of attraction between molecules • - Van der waals dipole-dipole forces • - When atoms of different electronegativities bond with each other to form a molecule, • the molecule that is formed has an unequal distribution of charge • - This unsymmetrical charge distribution results in the formation of a POLAR • molecule (dipoles – one side slightly negative, the other slightly positive) • - When polar molecules are close together they exert forces on each other

15. Alkyl halides - Alkane where one of the hydrogen atoms has been replaced with a halogen - R-X, where: X = F, Cl, I, Br Homologous series: CnH2n+1X Procedure for naming: - Determine length of longest chain (root name) - Start numbering from side closest to the first substituent (regardless of what it is) - If more than one type of halogen present, indicate the number using di, tri or tetra - If there are two different types of halogens in the molecule, each one present must receive its own number and be arranged in alphabetical order - Should the numbering of the root chain, from both sides, give the same smallest number, alphabetical preference is given to the one side

16. Structural and physical properties of alkyl halides 1) Alkyl halides have higher melting points and boiling points than alkanes with the same number of carbon atoms… - with alkane molecules, there are only London forces involved - with alkyl halides there are dipole-dipole forces involved too - the dipole-dipole forces are stronger and thus more energy is needed to separate the molecules 2) Melting points and boiling points of alkyl halides increases as the number of carbon atoms increases in the molecule… - As before, the greater the molecular mass of the molecules, the stronger the forces involved 3) Melting points and boiling points of alkyl halides increases as the size of the halogen atom increases (F < Cl < Br)… - The larger the group, the more surface area 4) Melting points and boiling points of alkyl halides decreases with an increase in the number of branches and unsaturated bonds - moving the halogen atom closer to the centre of the chain causes the molecule to become more circular and thus reduces the surface area

17. Reactions of organic molecules

18. Combustion (oxidation) • Reaction of alkanes with oxygen • Forms H2O and CO2 or CO • In the presence of sufficient oxygen… • In the absence of sufficient oxygen… • Consider: n = 1, 2, 3, 4

19. Substitution (halogenation) • Alkanes react with halogens (F2, Cl2, Br2) when heated or in the presence of light • Heated indicated with: D and light indicated: hf hf D • Examples: methane reacting with chlorine ethane reacting with bromine pentane reacting with flourine • Substitution in alkanes occurs when one or more hydrogen atoms in an alkane molecule are substituted by another atom or group of atoms. Energy in the form of sunlight or heat is necessary for the reaction to occur • Note: - The product that is formed is known as an alkyl halide or haloalkane - The reaction is often difficult to control, and further substitution can occur, replacing all the hydrogen atoms with halogen atoms

20. Elimination • Elimination reactions involve the removal of a smaller molecule out of a larger molecule • An important example of the this type of reaction is “CRACKING” • This involves the division of a larger hydrocarbon chain into smaller chains Pt 800OC • Depending on the length of the chain, multiple cracking sequences can occur • Consider the cracking of butane (3 possible products) • Not all products will produce the same yield

21. Addition reactions of the alkenes • An addition reaction is a chemical reaction where a molecule attaches to a double or triple bond of a second molecule to form a single molecule. During the reaction the multiple bond is broken and new atoms are added to the molecule to form a more saturated product • Examples of addition reactions… 1) Hydrogenation (adding two hydrogen atoms) - The catalyst (Pt, Ni, Pd) lowers the activation energy of the reaction by providing an area where the reactants can come into closer contact with one another 2) Halogenation (adding two halogen atoms) Note: The halogenation reaction where Br2 is added is the test for unsaturated hydrocarbons - A solution containing a saturated hydrocarbon will discolour with the addition of bromine water

22. 3) Hydrohalogenation (addition of hydrogen halides to alkenes) Note: Markovnikov’s rule… - When a polar molecule (eg. H-F, H-Cl, H-Br, H-I, H-OH) is added to a hydrocarbon double bond, the hydrogen atom is added to the carbon atom with the most H- atoms while the negative part of the molecule (F, Cl, Br, etc) is added to the carbon atom with the most alkyl substituents Note: In practice, 2-bromopropane

23. Hydration (addition of water to alkenes) - In the presence of a catalyst (H2SO4), water is added to an alkene to form an alcohol - One of the hydrogen atoms in the water molecule (H-OH) will bond to the carbon atom of the double bond (obeying the Markovnikov rule) Examples: - hydration of 2-methylpropene - hydration of 1-methyl-1-cyclohexene

24. Addition reactions of the alkynes • Just like alkenes, alkynes can also undergo addition reactions (result of unsaturated nature) 1) Hydrogenation (addition of hydrogen) - 2 possible products - The reaction can be stopped at the intermediate product (alkene) - Or it can convert the alkyne all the way to the saturated alkane

25. (2) Halogenation (addition of halogens) - 2 step process - The solution changes from orange-brown to colourless (3) Hydrohalogenation (addition of halogen and hydrogen) - 2 step process - The markovnikov rule applies

26. Alkyl halides are easily converted to other functional groups • The halogen atom, together with its bonding electron pair (halogens more electron negative than carbon) can leave the alkyl molecule to form a stable halide ion • We say that the halide is a good “LEAVING GROUP” • Note: Nu- is a Nucleophile (nucleus loving species) • Reaction with potassium/sodium hydroxide (alcohol formation) • - Alkyl halides don’t mix with water, so before treating them with the strong base (KOH or NaOH), they must be mixed in ethanol Substitution reactions with alkyl halides

27. Reaction with water - hydrolysis (alcohol formation) - Alkyl halides don’t mix with water, therefore they must be mixed in ethanol • Reaction with ammonia (amine formation) - Alkyl halides don’t mix with water, therefore they must be mixed in ethanol - This reaction takes place under high pressure conditions

28. Elimination reactions with alkyl halides • During an elimination reaction of alkyl halides, the halogen atom and the hydrogen atom of the adjacent carbon atom are removed from the molecule • Reaction with potassium/sodium hydroxide (alkene formation) - This reaction is known as a “Dehydrohalogenation” reaction - It can only occur if the alkyl halide is heated in the presence of the strong base Note: Some alkyl halides (more than 3 carbon atoms) can produce 2 different alkenes as products of elimination…

29. Note: One product is more favoured than the other (follows Zeitzev’s rule) “If more than one product is possible during elimination, the main product will be the alkene with the highest substituted double bond” Note: Substitution and elimination reactions compete with each other under the conditions of strong base (KOH or NaOH) addition… the preferred product formed depends on whether a PRIMARY, SECONDARY or TERTIARY halide is involved! Primary Secondary Tertiary Primary Halides - Substitution Secondary halides - Substitution / elimination Tertiary halides - Substitution / elimination

30. Aromatic hydrocarbons Aromatic compounds contain one or more benzene rings Benzene (C6H6) – simplest aromatic hydrocarbon The electrons in the double bond in benzene are able to move around in the ring The electrons are “delocalised” Thus the double bonds are able to move around the ring Naming aromatic compounds… All compounds based on a benzene ring have their names ending with “benzene” The naming of substituents work the same as in any other orgainc molecule Many single substituted rings have common names, Examples:

32. Benzene doesn’t undergo addition reactions (even though there is a high measure of unsaturation) as any addition reaction will result in the very stable conjugation of the double bonds being disrupted! • It undergoes substitution reactions, where one of the hydrogen atoms are replaced with a different atom (example: halogen atom)

33. FUNCTIONAL GROUPS CONTAINING OXYGEN • ALCOHOLS AND ETHERS • Homologous series: CnH2n+1OH • Shortened notation: ROH • Naming compounds containing alcohol groups - The name is derived from the alkane (longest chain) with the suffix “-ol” - The position of the –OH group is indicated according to the regular numbering system used with molecules containing other functional groups - Compounds that contain more than 1 –OH group are called (di, triols) • Physical properties of alcohols - Alcohols have a polar –OH group as well as a non-polar hydrocarbon part - Thus we have two types of bonding present: 1) Hydrogen bonding (between –OH groups) 2) Van der Waals forces (between alkyl groups)

34. But… is an alcohol molecule polar or non-polar? • It depends on the size of the non-polar alkyl group! • The larger the alkyl group gets, the more significant it becomes in the molecule and thus the compound becomes less soluble in water (ie: more non-polar) • Rule: When there are 4/more carbon atoms in the dominant part of the molecule, the molecule is considered non-polar (thus insoluble in water) • But… alcohols with branched alkyl groups are more soluble in water than those without branches! Because the branch decreases the contact surface of the non-polar part of the molecule! • Boiling and melting points - Consider the table of boiling points on page 76 - The presence of strong hydrogen bonding between alcohol molecules increases the boiling points of alcohols (compared to alkanes – van der waals forces) - It can also be seen that the boiling points of the alcohols increases as the number of carbon atoms in the molecule increases – this is due to van der waals forces

35. Chemical properties of alcohols - Alcohols are prepared by the ADDITION of WATER to an ALKENE (hydration) or through SUBSTITUTION of a HALOGEN (hydrolysis) - The following reactions are important to know… Oxidation of alcohols - Note: When Primary, secondary and tertiary alcohols undergo oxidation reactions, they form different products (functional groups) - Oxidation of PRIMARY alcohols - Acidified potassium dichromate (K2Cr2O7) or potassium permanganate (KMnO4) are excellent oxidizing agents - Primary alcohols react to form ALDEHYDES (R-CHO) and if heated further form CARBOXYLIC ACIDS (R-COOH) - When an orange potassium dichromate solution is used, green chromium ions will be formed, and when a purple KMnO4 solution is used it will form, a colourless solution of manganese ions

36. Oxidation of SECONDARY alcohols - Secondary alcohols react to form KETONES (ROR’) when heated in an acidified solution containing a powerful oxidizing agent - Tertiary alcohols do not react with acidified KMnO4 solutions (why not?) • Substitution reactions of alcohols - Alcohols react with anhydrous halides (HI, HCl and HBr) to form alkyl halides - This substitution reaction is the reverse of the hydrolysis (forming alcohols)

37. Elimination of alcohols - Alcohols undergo the removal of water (dehydration) to form alkenes - When an alcohol is heated with sulfuric acid (H2SO4) or Phosphoric acid (H3PO4) as catalysts, the alcohol loses the –OH group and an –H atom from the adjacent carbon to form an alkene! - Question: Can Methanol undergo elimination?! - Note: Some alcohols can produce 2 different alkene products (Zaitsev’s rule) Consider the summary of reactions on page 78 • ETHERS - Ethers are compounds that have an oxygen atom between 2 carbon atoms - General formula: R – O – R’ - When studying ethers, it can be seen that they are similar to alcohols, except that an alkyl group (R) is in the place of one of the hydrogen atoms!

38. Naming ethers - Ethers are named by giving the name of each alkyl group attached on either side of the oxygen atom, followed by the word “ether” - The alkyl groups are named in alphabetical order - Example: consider the molecule R – O – R’ where… • Physical and chemical properties - The boiling points of ethers are much lower than those of the alcohols - The boiling points are quite similar to those of the corresponding alkanes with a similar molecular mass - Question: What does this say about the forces between ether molecules?!

39. ALDEHYDES AND KETONES Aldehydes and ketones are compounds that have a CARBONYL group A carbonyl group is a group containing an oxygen atom that is bonded with a double bond to a carbon atom Aldehydes - contains a carbonyl group with at least one H-atom attached to it - the second group attached to the carbon can be another hydrogen (methanal) or it can be an alkyl group - Naming Aldehydes - aldehyde names end with “al” - The root name must contain the carbonyl group - numbering begins at the carbonyl group Ketones - Contains a carbonyl group that is bonded to two carbon atoms - Naming ketones - ketone names end with “one” - The root name must contain the carbonyl group - numbering begins at the end closest to the carbonyl group

40. Physical properties - aldehyde and ketone molecules cannot form hydrogen bonds, so it is expected that their boiling points be lower compared to the corresponding alcohols - Aldehydes and ketones are polar molecules because of the polar carbonyl functional group. Therefore, van der Waals dipole-dipole forces can exist between molecules. These forces are the reason that aldehydes and ketones have higher boiling points than non-polar alkenes or less polar ethers (consider table pg 92) - Aldehydes and ketones can form hydrogen bonds with water! - Thus they are soluble in water to a point. As with alcohols and ethers, the small molecules are soluble, but as the size of the alkyl group increases, the more Insoluble they become

41. CARBOXYLIC ACIDS • A carboxylic acid contains a carboxylic group, -COOH (carboxyl = carbonyl + Hydroxide) • General formula: CnH2n+1COOH • Naming carboxylic acids • - Carboxylic acids names end in “-oic acids” • - The root chain must contain the carboxylic group (numbering begins here) • - Number substituents according to position and arrange alphabetically • Preparing carboxylic acids • - Oxidation of an aldehyde (seen already) • Physical properties of carboxylic acids • - Very polar molecules (because the functional group is made up of two polar groups) • - ie. The hydroxyl group (-OH) and carbonyl group (C=O) • - The carboxylic acid molecules can form bonds with water and other carboxylic acids

42. Boiling points - Carboxylic acids have higher boiling points than ketones and aldehydes - Carboxylic acids have higher boiling points than alcohols even! - This is due to the fact that 2 hydrogen bonds form between 2 carboxylic acid molecules compared to the 1 between 2 alcohol molecules • Solubility - Due to the polar nature of carboxylic acids, they are soluble in water - The solubility decreases as the size of the molecule increases - Molecules with… - up to 4 carbons = very soluble - up to 10 carbons = slightly soluble - more than 10 = insoluble • Chemical properties - carboxylic acids are weak acids (vinegar) and thus partly ionize in water CH3COOH + H2O  H3O+ + CH3CO-

43. ESTERS • Esters are derived from carboxylic acids • They contain a carboxylic group of which the hydrogen atom (of the hydroxyl group) has been replaced by an alkyl group (R’) • Esterification (formation of esters) - When a carboxylic acid (RCOOH) and an alcohol (R’OH) are heated in the presence of a catalyst (H2SO4) an ester (RCOOR’) is formed! And water eliminated (H2O – is obtained by removing OH and H from the reactants)

44. Naming Esters - Naming esters consists of two parts - The first part is derived from the root alcohol (R’OH) and the second part is derived from the carboxylic acid (RCOOH) - The name has the suffix “-oate” Consider the following… - Divide the ester between the C-atom of the carbonyl group and the O-atom bonded to the alkyl group - Name alcohol first according to the number of C-atoms (methyl) - name acid part according to number of C-atoms and add “-oate” - Thus… methylethanoate

45. - When there are substituents present – they get the number of the carbon atom to which they are bonded (numbering starts at C-atom closest to carbonyl group) - substituents on the alcohol part are the prefixes for the alcohol part of the name, while the substituents on the carboxyl part are the prefixes for the carboxyl part of the name! • Boiling points - Don’t form hydrogen bonds - Do form van der waals dipole-dipole forces - Thus have boiling points similar to aldehydes and ketones • Solubility - Small esters soluble in water (dipole-dipole) - But larger ones insoluble

46. AMINES AND AMIDES AMINES - Amines are seen as alkyl derivatives from ammonia (NH3) where 1, 2 or 3 hydrogen atoms are displaced by alkyl groups - amines have the general formula: RNH2 (primary), R2NH (secondary) or R3N (Tertiary) - Amines can also be ARYL substituted - example: phenylamine (aniline) - Naming amines (IUPAC) - General: - Longest chain must contain the N-atom - Numbering starts from side closest to amine group - secondary amines - The other (shorter) alkyl group bonded to N-atom is named as an N-alkyl substituent - Tertiary amines - The other (shorter) alkyl group bonded to N-atom is named as an N, N-alkyl substituent - Physical properties - Amines are polar molecules - Primary and secondary amines from intermolecular Hydrogen bonds - Thus primary and secondary amines have high boiling points - But, not as high as the alcohols (since Nitrogen is less electronegative than oxygen) - Thus the H --- N hydrogen bond is not as strong as the H --- O hydrogen bond

47. - It is not possible for tertiary amines to form hydrogen bonds as there are no more H-atoms bonded to the Nitrogen atom - Thus their boiling points are lower than the primary and secondary amines - Solubility - Smaller amines are soluble in water (because they can H-bond) - But… Amines with more than 5 carbons have their H-bonding reduced and thus their solubility decreases! • AMIDES - Amides are derivatives of carboxylic acids, they are formed by substituting the –OH group with an amine group - COOH becomes CONH2 - general formula: RCONH2 - Naming amines (IUPAC) - Amides are named as alkane amides - The suffix “–amide” is used - An alkyl group attached to an N-atom gets “N-alkyl” at the beginning of the amide • - Physical properties - Primary amides can form several bonds between molecules (high boiling point) - Boiling points of secondary amides lower (and tertiary much lower) - amides with 1 to 5 Carbons = soluble (but more then 5 insoluble)