Transcript IB Chemistry

Organic Chemistry HL2
Topics 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 structures
http://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
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 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 Groups
Name
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.
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.
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
10.2.3 Describe, using equations, the reactions of methane
and ethane with chlorine and bromine.
CH4 (g) + Cl2 (g)
UV
CH3Cl (g) + HCl (g)
Cl• + Cl• free radical formation
Cl2 + energy
H
Cl• +
H
C
H
H
H
H
H
H
C • + Cl
H
H + HCl
•C
H
Cl
H
C
H
Cl + 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?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
and/or
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.
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• 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-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.
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 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.
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.
CH3NH2 + H2O
RNH3+ + OH-
Neutralization
CH3CH2NH2 + HCl
CH3CH2NH3+Cl-
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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?v=Do8ugMm-vMs
• 20.2.3 Explain how the rate of Sn1/Sn2 in halogenoalkanes by OHdepends 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 KCN
http://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.
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?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 acids
http://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
cycloalkanes
http://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