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REVIEWTOPIC 10/20: ORGANIC CHEMISTRY
A. KEY DEFINITIONS (MEMORIZE!)
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No explicit stating of definitions required in this unit.
B. YOU SHOULD KNOW:
 Two major features of a homologous series are that each member of the series differ from the previous one by
CH2, and they have the same functional group and thus similar chemical properties
 Also they have the same general formula and their physical properties gradually change with increasing chain
length as London forces increase
 Molecules with the same molecular formula such as C4H10 may be arranged in space in different ways, for example
CH3CH2CH2CH3 or CH3CH(CH3)CH3, and these are called structural isomers
 How to use the IUPAC rules for naming compounds containing up to six carbon atoms
 The terms primary, secondary and tertiary to describe carbon atoms (esp. in alcohols, halogenoalkanes and
amines)
 Alkanes are generally unreactive, because both the C-C and C-H bonds are strong and also non-polar
 Alkanes have very similar electronegativities
 Alkanes undergo combustion – they burn very exothermically in oxygen to produce carbon dioxide CO2 and water
H2O (this is complete combustion), for example CH4(g) + 2O2(g)  CO2(g) + 2H2O(g) or if oxygen is limited they can
produce poisonous carbon monoxide, CO, and/or soot (black carbon, C) also
 Alkanes react with chlorine and bromine in the presence of ultraviolet light (sunlight) via a free-radical substitution
reaction.
 The general formula of alkenes is C2H2n
 Alkenes are hydrocarbons containing a double bond between carbons that makes them more reactive than alkanes
 Alkenes undergo addition reactions with hydrogen, halogens, hydrogen halides and water via electrophilic addition
and adhere to Markovnikov’s Rule. (*Tertiary carbocations intermediates are more stable than secondary
carbocations which are more stable than primary carbocations.)
 Alkenes (monomers) can join to each other by addition polymerization to give long chain molecules (polymers).
 All alcohols contain the OH functional group and so can hydrogen bond with water and each other
 Alcohols will combust in oxygen and are good fuels
 Alcohols can undergo oxidation if they are reacted with acidified potassium dichromate(VI).
 That halogenoalkanes react with sodium hydroxide to produce alcohols via nucleophilic substitution
 SN1 = nucleophilic substitution with unimolecular, first-order kinetics
 SN2 = nucleophilic substitution with bimolecular, second-order kinetics
 Aldehydes and carboxylic acids can undergo reduction in the presence of a suitable reducing agent.
 Esters are formed when alcohols react with carboxylic acids via a condensation reaction – water is the inorganic
product of the reaction
 Nitrobenzene is synthesized via electrophilic substitution in the presence of nitric and sulfuric acid
 Phenylamine (analine) can be synthesized via the reduction of nitrobenzene
 Some important reaction pathways include:
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Stereoisomers have the same molecular formula and structural formula and, but their atoms are arranged
differently in space
Cis/trans isomers can occur when there is an alkene ore a cycloalkane, because it is not possible for the atoms to
rotate around without breaking a bond, so they are fixed in space next to each other (cis) or opposite each other
(trans)
Cis/trans isomers might have different physical or chemical properties, maybe because one is polar and the other
is not (for example, cis-1,2-dichloroethane is polar but trans-1,2-dichloroethane is non-polar, because the dipoles
cancel out)
The E/Z system is based on a set of priority rules
Conformational isomerism is a form of stereoisomerism in which the isomers can be interconverted exclusively by
rotation about single bonds
Optical isomers form when a carbon atom is chiral, which means that it is attached to four different groups
Optical isomers are mirror images of each other, and the only property that is different is their ability to rotate a
plane of polarized light in opposite directions
Optical isomers are described as l (rotate to the left) or d (rotate to the right)
C. YOU SHOULD BE ABLE TO:
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Predict and explain the trends in the boiling points of members of a homologous series
Represent the structural formula of a molecule using either a condensed or a complete formula – for example,
butane C4H10 could be represented:
CH3CH2CH2CH3
(condensed formula)
(complete structure)
Distinguish between the empirical formula, which is a ratio of elements, and the molecular formula, which gives
the actual number of atoms of each element – for example, the molecular formula of but is C4H10 but its empirical
formula is C2H5.
Deduce the structural formula of the isomers of compounds containing up to six carbons and the following
functional groups: alcohol, aldehyde, ketone, carboxylic acid and halide
Relate the volatility (boiling point) and solubility in water to the structure of the organic molecule and the
intermolecular forces holding the molecules together – for example, ethanol has an –OH functional group, which
can hydrogen bond to water, making it soluble in water, and it can hydrogen bond to other alcohol molecules,
giving it a relatively high boiling point
Describe the free-radical substitution mechanism using the terms initiation, propagation and termination
Describe initiation in terms of hemolytic fission, which leads to the formation of free radicals, which are denoted
using a black dot (e.g., Cl•….represents a chlorine free radical)
Distinguish between alkenes and alkanes using bromine water – alkenes decolourize it and alkanes do not
Outline the polymerization of alkenes to form polyethene, polypropene and PVC (polychloroethene).
Write equations for the combustion of alcohols
Describe the conditions needed during oxidation to produce an aldehyde (by distilling off the product as it forms)
and a carboxylic acid (by heating the alcohol under reflux).
Explain the process of nucleophilic substitution with equations and mechanisms
Show that SN1 occurs with tertiary halogenoalkanes and SN2 occurs in primary halogenoalkanes – secondary
halogenoalkanes can react via both mechanisms.
Explain why hydroxide is a better nucleophile than water
Describe/explain the factors that affect the rate of nucleophilic substitution
Suggest how to form a molecule if given a starting product (up to four steps)
Identify when cis/trans isomerism is taking place and be able to draw the cis and trans isomers and suggest how
their properties might vary
Identify the chiral carbon atom in a molecule and draw optical isomers in three dimensions as mirror images of
each other
Describe how a polarimeter works by shining a plane of polarized light through an isomer and measuring how
much this plane of light has been rotated
Provide evidence that supports the delocalized model/structure of benzene.
D. BE PREPARED
 You must learn the following names and structures.
NAME
MOLECULAR
EMPIRICAL
STRUCTURAL
FORMULA
FORMULA
FORMULA
Methane
CH4
CH4
CH4
Ethane
C2H6
CH3
CH3CH3
Propane
C3H8
C3H8
CH3CH2CH3
Butane
C4H10
C2H5
CH3(CH2)2CH3
Pentane
C5H12
C5H12
CH3(CH2)3CH3
Hexane
C6H14
C3H7
CH3(CH2)4CH3
GENERAL
FORMULA
CnH2n+2
CnH2n+2
CnH2n+2
CnH2n+2
CnH2n+2
CnH2n+2
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You must learn the following functional groups (names and structures).
NAME
FUNCTIONAL GROUP FORMULA EXAMPLE OF FORMULA
Alcohol
-OH
CH3CH2OH
Aldehyde
-CHO
CH3CHO
Ether
-OCH3-O-CH2CH3
Ketone
-CO
CH3COCH3
Carboxylic acid
-COOH
CH3COOH
Halide
-Cl, -Br, -I or -F
CH3CH2Cl
Alkene
-C=CCH2CH2
Amine
-NH2
CH3CH2NH2
*Benzene ring
C6H6 or
C6H5CH3
Ester
-COOHCOOCH3
Amide
-CONHCH3CONH2
Nitrile
-CN
CH3CN
*Not required to name benzene compounds (i.e., aromatics)
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EXAMPLE OF NAME
Ethanol
Ethanal
methoxyethane
Propanone
Ethanoic acid
Chloroethane
Ethene
Ethanamine
Methylbenzene
Methyl methanoate
Ethanamide
Ethanenitrile
Be able to write equations for the complete and incomplete combustion of alkanes.
Learn the following free-radical substitution mechanism:
Cl2  2Cl•
CH4 + Cl•  CH3• + HCl
CH3• + Cl2  CH3Cl + Cl•
Termination
Cl• + Cl• Cl2 or CH3• + CH3•  C2H6 or CH3• + Cl•  CH3Cl
Alkenes are very important as they form the basis of the plastics industry.
Also, hydration of ethane forms ethanol industrially, and unsaturated fats are hydrogenated to make margarine.
Primary alcohols are oxidized to aldehydes and then to carboxylic acids.
Secondary alcohols are oxidized to ketones.
Tertiary alcohols cannot be oxidized.
You must be able to draw mechanisms for SN1 and SN2 using curly arrows to show the movement of pairs of
electrons, as shown below.
SN2:
Initiation (in UV light)
Propagation
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During nucleophilic substitution, heterolytic fission occurs, because when a bond breaks both the electrons in a
covalent bond are transferred to one atom.
You must make sure that the positions of your curly arrows are very exact when drawing mechanism, because they
show the movement of the electron pair
You must be able to draw mechanisms for electrophilic addition and electrophilic substitution using curly arrows
to show the movement of pairs of electrons
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Esters are used as perfumes.
If a substance with a chiral carbon does not rotate the plane of polarized light, then it is a racemic mixture – there
is 50% of the l isomer and 50% of the d isomer.
Plane-polarized light is light where all the waves are in the same phase – it is like a 2-dimensional sheet of light.
You should be able to make three-dimensional drawings of chiral molecules (i.e., a pair of enantiomers) like the
following:
PROBLEM SET #10 (TOPIC 10/20)
*Reaction Pathways…sample questions from past exams:
1. Suggest how but-2-ene could be converted to butanone in two steps. Include the reagents and conditions needed and
write equations to describe each step.
2. Suggest how methane could be converted to methanol in two steps. Include the reagents and conditions needed and
write equations to describe each step.
*Stereoisomerism:
3. (a) Compounds of formula C4H7Cl exhibit both geometrical and optical isomerism.
(i) Explain why C4H7Cl shows geometrical isomerism.
(ii) Draw the cis and trans isomers of C4H7Cl.
(iii) Draw the structural formula of C4H7Cl that shows only optical isomerism. Indicate the chiral carbon using an asterisk.
b) Explain why 1,2-dichlorocyclopropane has cis and trans isomers. Draw the structural formulas of the two isomers.