Organic Chemistry HL2Topics 10 and 20

IB Chemistry Gr 12

Review Objectives (Topic 10)

• 10.1.1 Describe the features of a homologous series.• 10.1.2 Predict and explain the trends in boiling points of members

of a homologous series.• 10.1.3 Distinguish between empirical, molecular and structural

formulas.• 10.1.4 Describe structural isomers as compounds with the same

molecular formula but with different arrangements of atoms.

10.1.1 Describe the features of a homologous series.• Homologous series have the same general formula

with the neighboring members of the differing by a -CH2- unit.

• Members of a homologous series have similar chemical properties and show a gradual change in physical properties – as mass changes so do van der Waals forces and sometimes the polarity of the molecules.

10.1.2 Predict and explain the trends in boiling points of members of homologous series.

Alkane Boiling Point °C

Methane, CH4 -164

Ethane, C2H6 -89

Propane, C3H8 -42

Butane, C4H10 -0.5

Pentane, C5H12 36

Hexane, C6H14 69

Heptane, C7H16 98

Octane, C8H18 125

• Note the trend in b.p. is predictable due to increase in van der Waals’ forces with mass but it is not linear – the increase in chain length is proportionally greater for the small chains.

• Other physical properties that vary predictably are density and viscosity.

Properties • Most organic compounds tend to be non-polar and will

just have van der Waals forces and be insoluble in water.

• Some functional groups contain oxygen and nitrogen and will give rise to dipole-dipole interactions and/or hydrogen bonding.

• Some functional groups will also interact with water like acids or bases so they will affect the pH.

• The longer the non-polar hydrocarbon chain, the less likely a molecule will mix with polar solvents like water.

10.1.3 Distinguish between empirical, molecular and structural formulas.

• Empirical: simplest ratio of atoms ex. C2H4O• Molecular: actual number of atoms ex. C4H8O2

• Structural (condensed): shows overall structure ex. CH3CH2CH2COOH

• Full structural (displayed): shows every bond and atom ex.

http://www.youtube.com/watch?v=WkeOPe-Ia0U&feature=em-subs_digest-vrecs

Review Objectives• 10.1.4 Describe structural isomers, same molecular formula

but different structureshttp://www.youtube.com/watch?v=Wp7v6D8BgyQ

• 10.1.5 Deduce structural formulas for the isomers of the non-cyclic alkanes up to C6.

http://www.youtube.com/watch?v=JvLyQC_FNxg

• 10.1.6 Apply IUPAC rules for naming the isomers of the non-cyclic alkanes up to C6.

http://www.youtube.com/watch?v=nS9I_c9lYYA

Review Objectives• 10.1.7 Deduce structural formulas for the isomers of the straight

chain alkenes up to C6.

http://www.youtube.com/watch?v=WBzG5iOD6H4

• 10.1.8 Apply IUPAC rules for naming the isomers of the straight chain alkenes up to C6.

http://www.youtube.com/watch?v=LI5Zmh_naqU

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Classification of Hydrocarbons

Hydrocarbons are made up of only hydrogen and carbon.

Alkanes, Alkenes, Alkynes, • Alkanes are SATURATED as they only have single

bonds.• Alkenes and alkynes are UNSATURATED as they contain

multiple bonds. These bonds are stronger and mean that the molecules can react more.

• Alkenes contain a C=C bond.• Alkynes contain a C=C triple bond.• Alkenes are very important in the petrochemical

industry as they are the starting substances to make many other compounds, such as polymers (plastic).

How to name organic compounds

1. Identify the longest carbon chain. Ex. pent- for 5 Cs in the longest chain.

2. Identify the type of bonding in the chain or ring.3. Identify the functional group joined to the chain or

ring. This may come at the beginning or the end. Ex. Ethanol (alcohol)

4. Numbers are used to give the position of groups or bonds in the chain.

ex. But-1-ene

Objectives• 10.1.9 Deduce structural formulas for compounds containing

up to six carbon atoms with one of the following functional groups: alcohol, aldehyde, ketone, carboxylic acid and halide.

• 10.1.10 Apply IUPAC rules for naming compounds containing up to six carbon atoms with one of the following functional groups: alcohol, aldehyde, ketone, carboxylic acid and halide.

http://www.youtube.com/watch?v=sd3YfPbPTgY

• 10.1.11 Identify the following functional groups when present in structural formulas: amino (NH2), benzene ring, and esters (RCOOR).http://www.youtube.com/watch?v=2sRNlhaYZDQ

Objectives• 10.1.12 Identify primary, secondary and tertiary carbon atoms in alcohols

and halogenoalkanes.• 10.1.13 Discuss the volatility and solubility in water of compounds

containing the functional groups listed in 10.1.9.• http://www.youtube.com/watch?v=pH51q_YOluE

• 20.1.1 Deduce the structural formulas for compounds containing up to six carbon atoms with one of the following functional groups: amine, amide, ester and nitrile.

• 20.1.2 Apply IUPAC rules for naming compounds containing up to six carbon atoms with one of the following functional groups: amine, amide, ester, and nitrile.

• http://www.youtube.com/watch?v=0BHrXS9Zvt4

Functional GroupsName Functional Group Prefix/suffix Example

Alkane None -ane CH4, methane

Alkene C=C -ene CH2=CH2, ethene

Alkyne C=C -yne CH=CH, ethyne

Alcohol -OH -anol (or hydroxy) CH3OH, methanol

Aldehyde -CHO -anal CH3CHO, ethanal

Ketone -CO -anone CH3COCH3, propanone

Carboxylic Acid -COOH -anoic acid CH3COOH, ethanoic acid

Halogenoalkane -X (F, Cl, Br or I) Halogeno- (fluoro ) CH3CH2Cl, chloroethane

Amine -NH2 -ylamine (or amino) CH3CH2NH2, ethylamine

Amide -CONH2 -anamide CH3CONH2, ethanamide

Ester R-CO-O-R’ Alkyl -alkanoate CH3COOCH3, methyl ethanoate

Nitrile -CN -anenitrile (or cyano-)

CH3-CN, ethanenitrile (cyanomethane)

10.1.13 Discuss the volatility and solubility in water of compounds containing the functional groups listed in 10.1.9 (alcohol, aldehyde, ketone, carboxylic acid and halide.)

• Volatility is a measure of how easily a substance changes into gaseous state. High volatility means that a compound has a low boiling point.

• Effect on volatility of the different functional groups is summarized as:haloalkane>aldehyde> ketone> alcohol> carboxylic acid

• Solubility in water is increased by the presence of functional groups like alcohols, carboxylic acids and amines as these can all form hydrogen bonds.

• Aldehydes, ketones, amides and esters have polar bonds so will be soluble in water.http://www.youtube.com/watch?v=pH51q_YOluE

10.2 ALKANES

• 10.2.1 Explain the low reactivity of alkanes in terms of bond enthalpies and bond polarity.

Relatively strong bonds mean that the molecule needs a lot of energy added in order to start any reaction = low reactivity.

The molecule also has many non-polar or low polarity bonds so electrophiles (seeking negative places to react) and neucleophiles (positive places) will not be attracted to it.

Complete Combustion

CH4 (g) + 2O2 (g) CO2 (g) + 2H2O (l) H0 = -890.4 kJ/mo

10.2.2 Describe, using equations, the complete and incomplete combustion of alkanes

Do NOW

Write an equation for the incomplete combustion of methane.

Reactions of Methane and Ethane

• 10.2.3 Describe, using equations, the reactions of methane and ethane with chlorine and bromine.

http://www.youtube.com/watch?v=7sEfRaXdh5A

• 10.2.4 Explain the reactions of methane and ethane with chlorine and bromine in terms of a free-radical mechanism.

http://www.youtube.com/watch?v=ukxOtG7d3OA

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CH4 (g) + Cl2 (g) CH3Cl (g) + HCl (g)UV

Cl2 + energy Cl• + Cl• free radical formation

Cl• + C HH

H

H

C H

H

H

• + HCl

CH

H

H

• + Cl Cl C ClH

H

H

+ Cl•

10.2.3 Describe, using equations, the reactions of methane and ethane with chlorine and bromine.

10.2.4 Explain the reactions of methane and ethane with chlorine and bromine in terms of a free-radical mechanism.

• http://www.youtube.com/watch?v=ukxOtG7d3OA

• The reaction mixture is stable in the dark, but UV light will initiate the reaction. The halogen bond is broken by the UV light in homolytic fission. The chlorine radicals produced are very reactive. The reaction moves through propagation and termination.

10.3.1 Describe, using equations, the reactions of alkenes with hydrogen and halogens.Alkenes can be turned into alkanes by adding hydrogen (using heat and a nickel catalyst). Halogens can also be added to alkenes to make dihaloalkanes. BUT the halogens add onto each side of the C=C bond -- there is not enough room for the halogens to comfortably fit on only one carbon. These are both ADDITION reactions.http://www.youtube.com/watch?v=VtQRO4MFfmM

10.3.2 Describe, using equations, the reactions of symmetrical alkenes with hydrogen halides and water.Hydrating alkenes produces alcohols and hydrogenhalonating (nobody really uses this word) alkenes produces haloalkanes. Just add the small molecule across the C=C bond.http://www.youtube.com/watch?v=5z7seQ7IBsQ

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Markovnikov’s rule: in addition of unsymmetrical (that is, polar) reagents to alkenes, the positive portion of the reagent (usually hydrogen) adds to the carbon atom that already has the most hydrogen atoms.

and/or

• 10.3.3 Distinguish between alkanes and alkenes using bromine water.

http://www.youtube.com/watch?v=6FaBN70E2tM

ALKENES, C=C will decolorize bromine water (which is red). The double bond in the alkene breaks and a bromine atom bonds to the C on each side. ALKANES do not react -- so the red of the bromine persists.

• 10.3.4 Outline the polymerization of alkenes.http://www.youtube.com/watch?v=LYZP9LQd-doAlkenes behave as monomers (simple building blocks) that can be

joined together to form long chains called polymers. Ethene can make polyethene, propene can make polypropene etc. These are addition polymers - the reaction completely uses all the monomer, no extra small molecule is also produced like in condensation polymers.

10.3.5 Outline the economic importance of the reactions of alkenes

• Alkenes in vegetable oil can be removed by hydrogenation to make spreadable margarine -- and a profit. Ethene can also be hydrated to form the fuel ethanol. Alkenes are polymerized to make plastics such as polyethene or polypropene, with multiple uses as packaging, clothing etc.

Alkenes and Steam If superheated steam, H2O(g), is added to an alkene at 300°C and 7

atm, a reversible reaction occurs which produces ETHANOL.This is an important industrial process as ethanol is used in large

quantities as a solvent and an intermediate to make other compounds.

At 1 atm the eqm lies to the left and alkenes are formed by the dehydration of alcohols.

Catalyst used in both directions is concentrated H2SO4.

10.4 Alcohols

• 10.4.1 Describe, using equations, the complete combustion of alcohols.

• 10.4.2 Describe, using equations, the oxidation reactions of alcohols.

• 10.4.3 Determine the products formed by the oxidation of primary and secondary alcohols.

Alcohols• Their general formula is CnH2n+1OH.

• The -OH is polar which increases the volatility and the solubility in water compared to alkanes of similar mass.

• The best known alcohol is ethanol, C2H5OH,which dissolves readily in water and is present in alcoholic drinks.

• Ethanol for use in drinks is produced through fermentation of sugars like glucose – this is a slow process that requires warm anaerobic conditions.

• 3 Classes of Alcohols:1. primary: – has –OH attached to a terminal C.

2. secondary: has –OH attached to a middle C. 3. tertiary: has –OH attached to a C connected to 3 other Cs.

Oxidation of Alcohols• The H atoms attached to the C with the –OH

group are readily oxidized so these 3 classes of alcohols behave in different ways.

• A common oxidizing agent is acidified potassium dichromate(VI). H2SO4 is commonly used as the acid.

• Tertiary alcohols do not have any reactive H atoms and are not readily oxidized.

• Secondary alcohols have one reactive H and undergo oxidation to form ketones.

Oxidation of AlcoholsPrimary alcohols aldehydes carboxylic acids.• Both aldehydes and alcohols are polar but alcohols can participate in

hydrogen bonding in addition to dipole-dipole forces so they have higher boiling points. Aldehydes only have dipole-dipole forces.

• To obtain the aldehyde in the lab the alcohol is added to the boiling oxidizing agent so that as soon as the more volatile aldehyde is formed it distills off.

• To obtain the carboxylic acid rather than the aldehyde a more concentrated solution of the oxidizing agent is added and the mixture is refluxed so that the aldehyde cannot escape.

• Heating under reflux allows us to carry out a reaction at the boiling point of the solvent without any loss of the solvent.

• The vapor of the boiling solvent turns back to liquid in a vertical condenser and drips back into the flask.

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• Generally weak acids• React with alcohols to form esters

• Neutralization

•Production of acid halides (intermediates in syntheses)

Properties and Reactions of Carboxylic Acids

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Amines

Amines are organic bases with the general formula R3N.

CH3NH2 + H2O RNH3+ + OH-

CH3CH2NH2 + HCl CH3CH2NH3+Cl-

Neutralization

20.2 Nucleophilic Substitution

• 20.2.1 Explain why the hydroxide ion is a better nucleophile than water.

http://www.youtube.com/watch?v=Do8ugMm-vMs• 20.2.3 Explain how the rate of Sn1/Sn2 in halogenoalkanes by OH-

depends on if the halogenoalkane is primary, secondary or tertiary. – Sn2 reactions have higher activation energy (and an unstable reaction

intermediate) and so are slower than Sn1 reactions. (Sn1 is a 2 step process with tertiary haloalkanes – FAST)

http://www.youtube.com/watch?v=UJJAyJrv1o0• 20.2.4 Describe the substitution reactions of halogenoalkanes

with NH3 and KCN http://www.youtube.com/watch?v=z0ryePkDfrg

Nucleophilic Substitution

• 20.2.5 Explain the Sn2 reactions of primary halogenoalkanes with NH3 and KCNhttp://www.youtube.com/watch?v=aV_EH65e5G0

• 20.2.6 Describe the reduction of nitriles using H2 and Ni catalyst

• http://www.youtube.com/watch?v=khgVZp-1OcM

Elimination Reactions• 20.3.1 Describe, using equations, the elimination of HBr from

bromoalkanes

Warm OH-(aq) reacts with bromoalkanes by substitution (Sn1 or Sn2) BUT if hot OH-(ethanol) is used then an "elimination" reaction will occur and ethene will be the product. This shows that the same reactants but a different solvent can cause a different chemical reaction.

• http://www.youtube.com/watch?v=vK03vp3m2cA

• 20.3.2 Describe/explain the mechanism for elimination of HBr from bromoalkanes.

• http://www.youtube.com/watch?v=b9bHbtehQdQ

• No-one is quite sure how much detail the IB want here (text books disagree) -- so this video contain the most you need to know.

Condensation Reactions• 20.4.1 Reactions of alcohols with carboxylic acids to form esters.

State uses of esters.

Reacting an alcohol with a carboxylic acid in warm sulfuric acid produces an ester and water. This is a condensation reaction (a small extra molecule is produced -- in this case water). The sulfuric acid acts as a catalyst. The equation is in equilibrium.

Esters have a "fruity" smell (mostly), and are found in fruit. They also make good solvents due to their intermediate polarity (not polar -- not really non-polar!). They are also highly flammable.

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Esters

Esters have the general formula R′COOR, where R is a hydrocarbon group.

Hydrolysis

Alkaline hydrolysis (saponification)

Characteristic odors and flavors

Reaction Pathways

• 10.6.1 Deduce reaction pathways given the starting materials and the product.

• http://www.youtube.com/watch?v=2SabU1POXoQ

• 20.5.1 Deduce reaction pathways given the starting materials and the product. http://www.youtube.com/watch?v=0ujVlabZHT4

Condensation Reactions• 20.4.2 Describe, using equations, the reactions of amines with

carboxylic acids.Amines react with carboxylic acids to produce an amide

and a water molecule. This is a condensation reaction (the products include a small molecule and a larger product)http://www.youtube.com/watch?v=PEROYlrufqI

• 20.4.3 Deduce structures of the polymers formed by alcohols and carboxylic acidshttp://www.youtube.com/watch?v=gNAqy4eAbMU

• 20.4.4 Deduce the structures of the polymers formed by amines with carboxylic acids.http://www.youtube.com/watch?v=PobsIm1KeFg

Stereoisomerism

• 20.6.1 Stereoisomers-same structural formula, different spacial arrangement of atomshttp:http://www.youtube.com/watch?v=gpBjkp5HnkY

• 20.6.2 Geometric Isomerism in Alkenes• http://www.youtube.com/watch?v=twBagonrMLQ

Stereoisomerism• 20.6.3 Describe/explain geometrical isomerism in C3,C4

cycloalkaneshttp://www.youtube.com/watch?v=L_ZEXjYO8s8

• 20.6.4 Explain the difference in physical/chemical properties of geometrical isomers

http://www.youtube.com/watch?v=4E91aVgFodM• 20.6.5 Describe and explain optical isomerism in simple organic

molecules.• If a carbon atom in a molecule has 4 different atoms or groups attached it is

known as being "chiral" or "asymmetric". Such chiral carbons produce chiral molecules. A chiral molecule and the molecule that is its reflection are called "enantiomers". A 50:50 mixture of enantiomers is called "racemic". Butan-2-ol and 2-bromo butane are both chiral molecules.

http://www.youtube.com/watch?v=ujOgXeT-11A