Module 4 - Organic and Analytical Chemistry Flashcards
What makes carbon so special?
Carbon can bond to other carbon atoms to form long chains. Each atom can form 4 covalent bonds. Can form single, double, and triple bonds.
Define hydrocarbon.
Hydrocarbon - compound containing carbon and hydrogen only.
Define homologous series.
Homologous series - series of organic compounds having the same functional group but with each successive member differing by CH2.
Define functional group.
Functional group - group of atoms responsible for the characteristic reactions of a compound.
Define aliphatic.
Alicyclic - compound containing carbon and hydrogen joined together in straight chains, branched chains, or non-aromatic rings.
Define alicyclic.
Alicyclic - aliphatic compound arranged in non-aromatic rings with or without side chains.
Define aromatic.
Aromatic - compound containing a benzene ring.
Define saturated.
Saturated - containing single carbon-carbon bonds only.
Define unsaturated.
Unsaturated - presence of carbon-carbon multiple bonds.
What is an alkyl group?
Alkyl group - hydrogen removed from an alkane parent chain.
What are the rules for naming organic compounds?
Nomenclature: * Identify parent chain * Name stem of the parent chain * Identify alkyl chains and place the group names as prefixes * Identify functional groups and use the name for the prefix or suffix * Group together alkyl chains or functional groups that are the same (using di/tri/tetra) * Number every alkyl group and functional group to show their positions on the parent chain, consistently in the direction that would give the lowest number for the functional group that is named as the suffix * Order the prefixes in alphabetical order.
What is molecular formula?
Molecular formula - shows number and type of atoms of each element present in a molecule. Does not show how the atoms are joined.
What is empirical formula?
Empirical formula - simplest whole-number ratio of atoms of each element present in a compound.
What is general formula?
General formula - simplest algebraic formula for any member of a homologous series.
What is displayed formula?
Displayed formula - relative positioning of all atoms in a molecule and the bonds between them.
What is structural formula?
Structural formula - smallest amount of detail necessary to show arrangement of atoms in a molecule.
What is skeletal formula?
Skeletal formula - simplified displayed formula where you remove: * All carbon and hydrogen labels from carbon chains * Any bonds to hydrogens. In it: * A line represents a single bond * Intersection of two lines represents a carbon atom * End of a line represents a -CH3 group.
What are structural isomers?
Structural isomers - compounds with the same molecular formula but different structural formulae.
What is homolytic fission?
Homolytic fission - each bonded atom receives one of the shared pair of electrons from the bond.
What is heterolytic fission?
Heterolytic fission - one of the bonded atoms receives both of the electrons from the bond.
What is a radical?
Radical - species with an unpaired electron.
What are alkanes?
Alkanes - homologous series of saturated hydrocarbons. The single bonds are σ bonds.
What are σ bonds?
Sigma bonds - result of the direct overlap of two orbitals, one from each bonding atom. Sigma bonds can rotate.
Explain the tetrahedral shape of carbon atoms in alkanes.
Shape of alkanes: * There are 4 bonded pairs and 0 lone pairs around each carbon atom * Electron pairs repel each other as far apart as possible * Results in 109.5 bond angles - tetrahedral shape.
Explain the zigzag shape of alkanes.
Due to the 109.5 bond angles around each carbon atom, there cannot be a true straight line arrangement.
What are the factors affecting BP/MP of alkanes?
Factors affecting BP/MP of alkanes: * Chain length * Branching.
How does chain length affect BP/MP of alkanes?
Longer chain - more atoms - more electrons. More electrons - stronger London forces. Stronger forces holding molecules together - more energy is required to break the intermolecular bonds and separate molecules to move them apart and change state. So longer chain - higher MP/BP.
How does branching affect MP/BP of alkanes?
Higher branching - smaller contact area between molecules. London forces are weaker - less energy required to break IMF bonds - lower MP/BP.
Explain why alkanes are unreactive.
Contain only C-C and C-H sigma bonds that are strong & hard to break. C-C bonds are non-polar. C-H bonds have very small electronegativity difference - non-polar.
Why are alkanes used as fuel?
Readily available, easy to transport, burn in plentiful supply of oxygen without releasing toxic products.
What are the products of incomplete combustion?
Incomplete combustion: * Water * Carbon dioxide * Carbon monoxide * Soot (C). Can be any combination of the products but must have water.
What are the dangers of carbon monoxide?
Odorless, colorless and highly toxic. Forms carboxyhaemoglobin irreversibly preventing haemoglobin transport of oxygen around body.
Describe halogenation of alkanes, what type of reaction is it?
In presence of UV, alkanes react with halogens to form haloalkanes and hydrogen halides. Radical substitution reaction.
What are the steps of radical substitution of alkanes?
Steps of radical substitution: * Initiation * Propagation * Termination.
Describe the initiation stage.
Covalent bond in halogen molecule broken by UV radiation by homolytic fission. Each atom takes 1 electron from the bonded pair forming two radicals.
Why is halogenation of alkanes a substitution?
Example of a substitution because one of the Hs in the alkane has been replaced by a halogen molecule.
Describe the propagation stage.
Chain reaction: * First step: halogen radical reacts with C-H bond in alkane forming alkyl radical and a molecule of hydrogen halide. * Second step: each alkyl radical reacts with another halogen molecule forming a haloalkane and a new halogen radical, cycle repeats.
Describe the termination stage.
Two radicals collide forming a molecule with all electrons paired, stopping the chain reaction. Number of possible steps with different radicals.
What are the limitations of radical substitution in synthesis?
Limitations: * Further substitution can occur * Another halide radical can collide with a haloalkane molecule substituting a further hydrogen atom to a halogen * Substitution can occur at different positions on the carbon chain * Longer chain molecules can form isomers of the haloalkane - halogen radical attacks hydrogen on different carbon * Carbon chain may change in length * Two alkyl radicals can combine to form longer alkane.
What are alkenes?
Alkenes - unsaturated hydrocarbons containing a C=C bond.
Give the general formula for a non-cyclic alkene containing a C=C bond.
CnH2n.
Give the general formula of an alkane that contains additional C=C bonds.
CnH(2n-2x) where x - number of additional double bonds.
Explain how a sigma bond is formed from atomic orbitals.
Sigma bond - forms from direct overlap of orbitals.
Explain how a pi bond is formed from atomic orbitals.
Pi bond - sideways overlap of two adjacent p-orbitals above and below the bonding atoms.
Describe the structure of the double bond in alkenes.
Double bond: * 3 out of 4 electrons are used in three sigma bonds * 1 electron from each carbon atom is shared in the sideways overlap of two p-orbitals - the π bond. π bond electron density is concentrated above and below the joining nuclei of the bonding atoms. π bond locks the two atoms in place, preventing them from rotating around the double bond.
Explain the shape around a double bond.
Trigonal planar shape because: * Three regions of electron density around each of the carbon atoms, no lone pairs * They repel each other as far apart as possible - bond angle will be 120° * All the atoms are in the same plane.
Define stereoisomers.
Stereoisomers - molecules with the same structural formula but a different arrangement of atoms in 3D space.
What are the conditions for E/Z isomerism?
E/Z isomerism requirements: * C=C double bond * Different groups attached to each carbon atom of the double bond.
Why does E/Z isomerism occur?
Occurs because the π bond’s electron density above and below the plane of the sigma bond prevents the atoms from rotating around the bond.
What is cis-trans isomerism?
Cis-trans: Special case of E/Z isomerism in which one of the groups attached to each carbon of the double bond is the same. If they are on the same side of the double bond - cis, if on opposite side - trans.
What are the CIP priority rules for identifying E and Z stereoisomers?
Why are alkenes more reactive than alkanes?
Reactivity of alkenes: Presence of the π-bond in the C=C bond. π bond electron density is concentrated above and below the sigma bond. Because it is outside of the double bond - they are more exposed than the sigma bond electrons & π bond breaks relatively easily - requires less energy to break and undergo addition.
What are the conditions required for the addition of hydrogen to alkenes?
Ni catalyst at 150°C.
What are the conditions required for the addition of halogens to alkenes?
RTP and pressure.
What are the conditions for addition of hydrogen halide to alkenes?
RTP and pressure.
What are the conditions for the addition of water to alkenes?
Water as steam - (g) H3PO4 catalyst.
Define electrophile.
Electrophile - electron pair acceptor. Atom/group of atoms that is attracted to an electron-rich center. Usually cation or molecule containing a δ+ charge.
What causes bromine molecule to form a dipole?
A dipole is induced by the high electron density of the C=C.
What does a curly arrow represent in a reaction mechanism?
Curly arrow - movement of electrons.
What is the structural feature that allows species to act as nucleophiles?
Lone pair that can be donated to form a new covalent bond.
Define hydrolysis.
Hydrolysis - chemical reaction involving water or aqueous solution of a hydroxide that causes the breaking of a bond in a molecule.
What are haloalkanes?
Haloalkanes - compounds containing carbon, hydrogen and at least one halogen atom.
How are haloalkanes classified?
Explain how haloalkanes react.
Reactivity of haloalkanes: The halogen is more electronegative than the carbon atom - electrons closer to the halogen - polar bond. Carbon is slightly +ve and can attract a lone pair of electrons (a nucleophile). When a haloalkane reacts with a nucleophile, it replaces the halogen in a substitution reaction in nucleophilic substitution.
What is a nucleophile?
Nucleophile - an electron pair donor. Attracted to +ve charge.
Give examples of nucleophiles.
Why are haloalkanes generally more reactive than alkanes?
C-X bonds are weaker than C-H bonds & require less energy to be broken in order to react.
Why are fluoroalkanes less reactive than alkanes?
C-F has higher bond enthalpy.
Define electronegativity.
Electronegativity - ability of an atom to attract the shared pair of electrons in a covalent bond.
Draw the mechanism for hydrolysis of bromoethane.
Draw and label a reflux apparatus.
Define reflux.
Reflux - continual boiling and condensing of a reaction mixture back to the original container.
What is hydrolysis?
Chemical reaction involving water or aqueous solution of a hydroxide that causes the breaking of a bond in a molecule.
What does a curly arrow represent in a reaction mechanism?
Movement of electrons.
Define reflux.
Continual boiling and condensing of a reaction mixture back to the original container to ensure that the reaction takes place without the contents of the flask boiling dry.
How does reflux apparatus work?
As mixture boils, vapor rising will be condensed back down by water-cooled condenser without escaping through the top.
Why do organic compounds often require heating under reflux?
Organic compounds have simple molecular structures, so have relatively low boiling points, compared to ionic compounds such as salts.
How are alcohols prepared from haloalkanes?
Hydrolysis: Aqueous NaOH added and reaction heated under reflux.
What is the order of rate of hydrolysis of chloro-, bromo-, and iodoalkanes?
C-I > C-Br > C-Cl.
Explain the trend in rates of hydrolysis of primary haloalkanes.
In terms of bond enthalpy: C-Cl > C-Br > C-I. C-I bond is weaker than C-Br bond, which is weaker than C-Cl. Less energy required to break the C-I bond than other carbon-hydrogen bonds.
Describe how you would measure the rate of hydrolysis of primary haloalkanes.
Set up three test tubes with equal volume of ethanol and 2 drops of each haloalkane. Stand the tubes in hot water bath at set temperature. Add aqueous silver nitrate and start stopwatch. Observe precipitate formation.
What are organohalogens?
Molecules that contain at least one halogen atom joined to a carbon chain.
Why was hot water required in the hydrolysis experiment?
To increase the rate of reaction, otherwise it would be too slow.
Explain the two roles played by aqueous silver nitrate solution in the hydrolysis experiment.
- Provides water as reactant in hydrolysis reaction
- Silver ions trap halide ions released after hydrolysis, forming a precipitate.
What was the purpose of ethanol used in the hydrolysis experiment?
Acts as a co-solvent allowing water and haloalkane to mix & produce a single solution.
Why was it necessary to carry out hydrolysis using water rather than NaOH(aq)?
If OH- ions were present, Ag+ would react in silver nitrate to form a brown precipitate, masking silver halide precipitate formed.
Why did the AgNO3(aq) not form precipitate immediately when added to haloalkanes?
No halide ions present - halogen was still covalently bonded to haloalkane until hydrolysis occurred.
How is ozone formed?
Ozone formation involves the reaction of oxygen molecules with ultraviolet light.
How is ozone broken down?
Ozone breakdown occurs through photodissociation by UV radiation.
If ozone is constantly forming and breaking down, how can a steady concentration be reached?
Rate of formation = rate of breakdown, so overall concentration won’t change.
How does the ozone layer protect us?
Absorbs harmful UV radiation, breaking down ozone instead of letting it pass through.
What dangers do living organisms face in absence of ozone?
Increased risk of genetic damage and skin cancer.
What are CFCs and HCFCs?
- CFC - chlorofluorocarbon
- HCFC - hydrochlorofluorocarbon.
What are CFCs and HCFCs used for?
Refrigerants and aerosol propellants.
Why do CFCs and HCFCs persist in the lower atmosphere?
The C-F and C-Cl bonds are strong, so molecules don’t break down easily.
How do nitrogen oxide radicals form?
Nitrogen oxide radicals form naturally during lightning strikes.
What role do chlorine and nitrogen radicals take in ozone depletion?
They act as catalysts.
Explain why alcohols have relatively low volatility compared to alkanes.
Hydrogen bonds in alcohols require more energy to break than weaker London forces in alkanes.
Explain the high solubility of alcohols in water relative to alkanes.
Alcohols form hydrogen bonds with water, while alkanes do not; solubility decreases with increasing carbon chain length.
State the classification of alcohols.
- Primary
- Secondary
- Tertiary.
What happens to each reactant in oxidation of alcohols in terms of redox?
Alcohols are oxidized to aldehyde/ketone/carboxylic acid; Cr2O72- is reduced to Cr3+.
State the reaction & conditions for preparation of an aldehyde (butanal).
Oxidation of a primary alcohol under controlled conditions.
State the reaction & conditions for preparation of a carboxylic acid.
Oxidation of a primary alcohol with excess oxidizing agent.
State the reaction and conditions for oxidation of a secondary alcohol (propan-2-ol).
Oxidation with potassium dichromate under acidic conditions.
State the reaction and conditions for oxidation of a tertiary alcohol (2-methylpropan-2-ol).
No reaction occurs.
State the reaction and conditions for converting alcohol to alkene (cyclohexanol).
Dehydration: Heat under reflux with concentrated sulfuric/phosphoric acid.
State the reaction and conditions for alcohol undergoing substitution with hydrogen halide (hydrogen bromide).
Substitution: Heat under reflux with sulfuric acid and sodium bromide.
Give the reaction and conditions for esterification of ethanoic acid and methanol.
Heated under reflux with concentrated sulfuric acid catalyst.
Explain ester nomenclature.
Ester nomenclature is based on the alkyl group from the alcohol and the acyl group from the acid.
How does nitrogen oxide cause ozone layer to deplete, show mechanism and overall reaction.
Write out the photodissociation of CF2Cl2.
Write out the propagation steps of ozone depletion by CFCs.
Write out overall equation for ozone depletion.
Draw and label a reflux apparatus.
State Markowinkoff’s rule
Markowinkoff’s rule - when an asymmetric alkene reacts with a hydrogen halide or steam, the major product is always formed from the more stable carbocation
How do you test for unsaturation?
Describe expected observations from measuring rate of hydrolysis of 1-chlorobutane, 1-bromobutane and 1-iodobutane.
