Organic Chemistry HL2 Topics 10 and 20

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Organic Chemistry HL2Topics 10 and 20

• IB Chemistry Gr 12

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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.

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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.

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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.

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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.

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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?vWkeOPe-Ia0Ufeature
em-subs_digest-vrecs
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Review Objectives

• 10.1.4 Describe structural isomers, same
  molecular formula but different structures
• http//www.youtube.com/watch?vWp7v6D8BgyQ
• 10.1.5 Deduce structural formulas for the isomers
  of the non-cyclic alkanes up to C6.
• http//www.youtube.com/watch?vJvLyQC_FNxg
• 10.1.6 Apply IUPAC rules for naming the isomers
  of the non-cyclic alkanes up to C6.
• http//www.youtube.com/watch?vnS9I_c9lYYA

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Review Objectives

• 10.1.7 Deduce structural formulas for the isomers
  of the straight chain alkenes up to C6.
• http//www.youtube.com/watch?vWBzG5iOD6H4
• 10.1.8 Apply IUPAC rules for naming the isomers
  of the straight chain alkenes up to C6.
• http//www.youtube.com/watch?vLI5Zmh_naqU

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Classification of Hydrocarbons
Hydrocarbons are made up of only hydrogen and
carbon.
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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 CC bond.
• Alkynes contain a CC 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).

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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

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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?vsd3YfPbPTgY
• 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?v2sRNlhaYZDQ

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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?vpH51q_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?v0BHrXS9Zvt4

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Functional Groups
Name Functional Group Prefix/suffix Example
Alkane None -ane CH4, methane
Alkene CC -ene CH2CH2, ethene
Alkyne CC -yne CHCH, 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)
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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
• haloalkanegtaldehydegt ketonegt alcoholgt 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?vpH51q_YOluE

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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.

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

• Complete Combustion
• CH4 (g) 2O2 (g) ? CO2 (g) 2H2O (l)
  DH0 -890.4 kJ/mo

Do NOW Write an equation for the incomplete
combustion of methane.
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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?v7sEfRaXdh5A
• 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?vukxOtG7d3OA

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

HCl
Cl
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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?vukxOtG7d3OA
• 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.

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• 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 CC 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?vVtQRO4MFfmM
• 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 CC bond.
• http//www.youtube.com/watch?v5z7seQ7IBsQ

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and/or
Markovnikovs 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.
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• 10.3.3 Distinguish between alkanes and alkenes
  using bromine water.
• http//www.youtube.com/watch?v6FaBN70E2tM
• ALKENES, CC 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?vLYZP9LQd-do
• Alkenes 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.

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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.

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Alkenes and Steam

• If superheated steam, H2O(g), is added to an
  alkene at 300C 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.

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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.

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Alcohols

• Their general formula is CnH2n1OH.
• 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.

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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.

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Oxidation of Alcohols

• Primary 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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Properties and Reactions of Carboxylic Acids

• Generally weak acids
• React with alcohols to form esters
• Neutralization
• Production of acid halides (intermediates in
  syntheses)

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Amines
Amines are organic bases with the general formula
R3N.
Neutralization
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20.2 Nucleophilic Substitution

• 20.2.1 Explain why the hydroxide ion is a better
  nucleophile than water.
• http//www.youtube.com/watch?vDo8ugMm-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?vUJJAyJrv1o0
• 20.2.4 Describe the substitution reactions of
  halogenoalkanes with NH3 and KCN
• http//www.youtube.com/watch?vz0ryePkDfrg

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Nucleophilic Substitution

• 20.2.5 Explain the Sn2 reactions of primary
  halogenoalkanes with NH3 and KCN
• http//www.youtube.com/watch?vaV_EH65e5G0
• 20.2.6 Describe the reduction of nitriles using
  H2 and Ni catalyst
• http//www.youtube.com/watch?vkhgVZp-1OcM

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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?vvK03vp3m2cA

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• 20.3.2 Describe/explain the mechanism for
  elimination of HBr from bromoalkanes.
• http//www.youtube.com/watch?vb9bHbtehQdQ
• 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.

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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.
Characteristic odors and flavors
Hydrolysis
Alkaline hydrolysis (saponification)
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Reaction Pathways

• 10.6.1 Deduce reaction pathways given the
  starting materials and the product.
• http//www.youtube.com/watch?v2SabU1POXoQ
• 20.5.1 Deduce reaction pathways given the
  starting materials and the product.
• http//www.youtube.com/watch?v0ujVlabZHT4

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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?vPEROYlrufqI
• 20.4.3 Deduce structures of the polymers formed
  by alcohols and carboxylic acids
• http//www.youtube.com/watch?vgNAqy4eAbMU
• 20.4.4 Deduce the structures of the polymers
  formed by amines with carboxylic acids.
• http//www.youtube.com/watch?vPobsIm1KeFg

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Stereoisomerism

• 20.6.1 Stereoisomers-same structural formula,
  different spacial arrangement of atomshttp
• http//www.youtube.com/watch?vgpBjkp5HnkY
• 20.6.2 Geometric Isomerism in Alkenes
• http//www.youtube.com/watch?vtwBagonrMLQ

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Stereoisomerism

• 20.6.3 Describe/explain geometrical isomerism in
  C3,C4 cycloalkanes
• http//www.youtube.com/watch?vL_ZEXjYO8s8
• 20.6.4 Explain the difference in
  physical/chemical properties of geometrical
  isomers
• http//www.youtube.com/watch?v4E91aVgFodM
• 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 5050 mixture of enantiomers is
  called "racemic". Butan-2-ol and 2-bromo butane
  are both chiral molecules.
• http//www.youtube.com/watch?vujOgXeT-11A