Module 4.1 - Basic Concepts and Hydrocarbons Flashcards
What is nomenclature?
The system of naming compounds
What is a homologous series?
A series of organic compounds that have the same functional group with each successive member differing by CH2
What is an aliphatic hydrocarbon?
A hydrocarbon with carbon atoms joined together in straight or branched chains
What is an alicyclic hydrocarbon?
A hydrocarbon with carbon atoms joined together in a ring structure (not aromatic)
What is an aromatic hydrocarbon?
Contains at least one benzene ring
Are alkanes saturated or unsaturated?
Saturated
What is the first 10 compounds of the alkane homologous series and what is their formulae?
- methane, CH4
- ethane, C2H6
- propane, C3H8
- butane, C4H10
- pentane, C5H12
- hexane, C6H14
- heptane, C7H16
- octane, C8H18
- nonane, C9H22
- decane, C10H22
What are the first 10 alkyl groups and their formulae?
- methyl, CH3
- ethyl, C2H5
- propyl, C3H7
- butyl, C4H9
- pentyl, C5H11
- hexyl, C6H13
- heptyl, C7H15
- octyl, C8H17
- nonyl, C9H19
- decyl, C10H21
What is the formula, prefix and suffix of the alcohol functional group?
- OH
prefix: hydroxy-
suffix: -ol
What is the formula and suffix of the aldehyde functional group?
- CHO
- al
What is the suffix and formula of the alkane functional group?
C-C
-ane
What is the suffix and formula of the alkene functional group?
C=C
-ene
What is the formula and suffix of the carboxylic acid functional group?
- COOH
- oic acid
What is the formula and prefix for the haloalkane funcitonal group?
- F, fluoro-
- Cl, chloro-
- Br, bromo-
- I, iodo-
What is the formula and suffix of the ketone functional group?
C-CO-C
-one
What is a saturated compound?
Compounds that have only single bonds
What is a functional group?
A group of atoms that is responsible for the characteristic chemical reactions of a compound
What is the general formula of alkanes?
CnH2n+2
What is the general formula of alkenes?
CnH2n
What is the general formula of alcohols?
CnH2n+1OH
What is a general formula?
The simplest algebraic formula for a homologous series
What is a displayed formulae?
Shows the relative positions of atoms and the bonds between them
What is a structural formula?
Provides the minimum detail for the arrangement of atoms in a molecule
What is an empirical formula?
Shows the smallest whole number ratio of atoms of the elements in a compound
What is a molecular formula?
Shows the number and types of atoms in a compound
What is a skeletal formula?
A simplified structural formula drawn by removing hydrogen atoms from alkyl chains
What is an unsaturated compound?
Organic chemicals containing at least at leasy one carbon-carbon double covalent bond
What is a hydrocarbon?
Compounds that contain only hydrogen atoms and carbon atoms
In what 3 ways can structural isomers be formed?
- alkyl chains in different places
- functional group bonded to different parts of parent chain
- different functional group (e.g. aldehyde and ketone)
What is a structural isomer?
Compounds with the same molecular formula but different structural formulae
What is a stereoisomer?
Organic compounds with the same molecular formula and structural formula but have a different arrangement of atoms in space
What is cis-trans isomerism?
A type of E/Z isomerism in which the two substituent groups attached to both carbon atoms of the C=C bond are the same
What is E/Z isomerism?
A type of stereoismerism caused by the restricted rotation around the double bond - the two different groups are attacherd to both carbon atoms of the C=C double bond
How do you use the Cahn-Ingold-Prelog rule to identify and name E/Z isomers?
- Locate the C=C double bond and redraw it to show its substituents
- Focus on 1 C atom and assign priority of each substituent based on relative atomic mass (highest is given highest priority), then for the 2nd C
- If highest priority groups on the same side of C=C then it’s a Z-isomer but on different sides is an E-isomer
What is a covalent bond?
A strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
What is homolytic fission?
Happens when each bonding atom receives one electron from the bonded pair, forming 2 (highly reactive) radicals
X-Y → X• + Y•
What is a reaction mechanism?
Models that show the movement of electron pairs during a reaction
What are curly arrows used for?
Model the flow of electron pairs during reaction mechanisms
What is a radical?
A species with one or more unpaired electrons
Describe homolytic fission.
- one bonding atom receives both electrons from the (covalently) bonding pair
- results in a positive ion (cation) and negative ion (anion)
In what ways can a covalent bond form?
- radicals collide
- 2 oppositely charged ions collide
What is an alkane?
A homologous series of saturated hydrocarbons
What is the bond angle in alkanes?
- tetrahedral shape
- 109.5º
Why are alkanes considered to be non polar?
- carbon and hydrogen have similar Pauling electronegativity values
- bonds are non polar so no significant dipoles
- instantaneous dipoles may form from movement of electrons in shells causing lack of balance in charge distribution, which can cause induced dipoles (London force)
How does carbon-chain length affect the boiling point of alkanes?
- longer = increase in relative molecular mass
- larger = more areas of surface contact between adjacent molecules
- more induced dipole-dipole forces (London forces)
- more energy to overcome intermolecular attraction to change state
How does branching affect the boiling point of alkanes?
- more branched = fewer surfae area interactions between molecules as can’t fit together as neatly/closely
- branched = fewer induced dipole-dipole interactions (London forces) compared to straight chain isomer of same Mr so branched have lower bp than straight chain isomer
Why do alkanes have a relatively low reactivity?
- all covalent bonds in alkanes have high bond enthalpies so large amount of energy to break bonds
- C-H σ bonds have low polarity as electronegativities of carbon and hydrogen are almost the same
What energy transfer occurs in the combustion of alkanes?
- stored chemical energy transferred to usable forms like thermal energy
- combustion is a rapid oxidation reaction combining oxygen from air w another substance
Describe the complete combustion of alkanes, using methane as an example.
- plentiful supply of air
- clean, blue flame
- transfers max amount of thermal energy as oxidises hydrogen and carbon
- Bunsen burners burn methane
CH4 + 2O2 –> CO2 + 2H2O
Describe the incomplete combustion of alkanes, using methane as an example.
- limited supply of air
- produces soot (carbon particles)
- cooler, dirty yellow flame
- odourless, colourless, toxic CO formed
2CH4 + 2½O2 –> CO + C + 4H2O
2CH4 + 3½O2 –> CO2 + CO + 4H2O
3CH4 + 4½O2 –> CO2 + CO + C + 6H2O
What condition is needed to start a radical substitution reaction?
UV light
What are the stages of radical substitution?
- initiation: homolytic fission of a halogen forming radicals
- propagation: 2 repeated steps that bult up desired product in side reaction
- termination: 2 radicals collide and make a stable product
What are the problems with using radical substitution to form a desired product?
- unpredictable and difficult to control
- further substitution can take place to form a variety of organic products
- need to be separated e.g. by fractional distillation/chromatography so they can be used
Describe the chlorination of methane to form chloromethane.
–UV or temps of 300°C needed
- initiation: Cl2 –> 2Cl•
- propagation: CH4 + Cl• –> •CH3 + HCl
•CH3 + Cl2 –> CH3Cl + Cl• (desired product and chlorine radical)
-termination: 2Cl• –> Cl2
2•CH3 –> C2H6
•CH3 + Cl• –> CH3Cl
-further substitutions can produce hydrogen, chlorine, ethane, dichloromethane, trichloromethane, 1,2-dichloroethane, 1,2-dichloroethane, 1,1,2-trichloroethane, 1,1,1-trichloroethane, 1,1,2,2-tetrachloroethane, 1,1,1,2-tetrachloroethane, 1,1,1,2,2-pentachloroethane, 1,1,1,2,2,2-hexachloroethane
Describe the bromination of ethane.
- UV light
- initiation: Br2 –> 2Br•
- propagation: Br• + C2H6 –> •C2H5 + HBr
•C2H5 + Br2 –> C2H5Br + Br•
-termination: 2Br• –> Br2
2•C2H5 –> C4H10
•C2H5 + •Br –> C2H5Br
Describe the C=C bonding in alkenes.
- σ bond formed between 2 C atoms using direct overlap of electron clouds of 2 atoms
- π bond formed by electrons in adjacent p orbitals overlapping above and below C atoms. Can only be made after a σ bond is formed
- restricted rotation around C=C bond so have planar (flat) shape
Why does the alkene group have a high reactivity?
Has a high electron density
What is the bond angle around the alkene group?
120°
What is an alkene?
Homologous series of unsaturated hydrocarbons
What is an electrophile?
electron pair acceptor
What is the general equation for an electrophilic addition reaction?
Describe the hydrogenation of alkenes (electrophilic addition).
- 150ºC
- nickel catalyst
- forms the corresponding alkane
Describe the bromination of ethene (halogenation/electrophilic addition). What can this reaction be used for?
- aqueous bromine is non polar but has induced dipole when it gets close to C=C due to electron density
- electrons from π bond make bond w bromine causing heterloytic fission of bromine molecule. +ve charge on second carbon atom: reactive species called a carbocation
- 2 electrons from bromide ion shared w carbocation, making second bond and a stable product
- used to test for halogenation as goes colourless if reaction which indicates unsaturated as can undergo an addition reaction
- RTP?
Describe the hydration of ethene (electrophilic addition).
- steam
- H3PO4 catalyst
- 65 atm
- 300ºC
- makes alcohols
Describe the (electrophilic) addition of hydrogen bromide to ethene.
- produces a haloalkane (saturated organic compounds)
- gaseous hydrogen halides bubble through alkene for reaction
- large difference in negativity between H and Br so polar so permanent dipoles. 𝛿+ attracted to electron rich C=C
- electrons in π bond make a bond w H, causing heterlytic fission (e- go to bromine making bromide ion. Carbocation also made)
- bromide ion and carbocation bond to make a stable product
How does the number of alkyl chains on each carbon affect which carbon atom gets the hydrogen and the halide in the addition of a hydrogen halide to an alkene?
- Markownikoff’s rule: when H-X added to unsymmetrical alkene, H attached to C with most H atoms to start with as carbocations have alkyl groups attached are more stable than those w H atoms attached
- tertiary carbocations are most stable, primary carbocations are the least
- major product (more of) and minor product
What is a monomer?
Small molecules used to make polymers
What is a polymer?
Macromolecules made from small repeating units
What is a repeating unit?
A specific arrangement of atoms that occurs in a structure over and over again
What is the general equation for addition polymerisation?
What must the monomer used in addition polymerisation have?
a C=C double bond
What is the polymer of ethene and what is its uses?
- poly(ethene)
- plastic bags and bottles
What is the polymer of propene and what are its uses?
- poly(propene)
- ropes and crates
What is the polymer of chloroethene and what are its uses?
- poly(chloroethene) (PVC)
- electrical cable insulation
What is the polymer of phenylethene and what are its uses?
- poly(phenylethene) (polystyrene)
- packaging
What is the polymer of tetrafluoroethene?
- poly(tetrafluoroethene) (Teflon®)
- non stick coating on cooking pans
In what ways can polymer waste be dealt with?
- landfill (anaerobic conditions and limited H2O so reduced rate of decomposition of biodegradable materials, plastic danger to wildlife)
- combustion (releases CO2 and other toxic gases e.g. HCl removed by scrubbers like CaO, a base to neutralise)
- combustion w electrical generation (plastic have high calorific value so burnt to turn turbines)
- reusing
- recycling (expensive)
- using them as organic feedstock (chemical reaction break polymer to small organic molecules. Recovered chemicals can be used in other industrial reactions)
What are biodegradable polymers?
- biodegradable polymer e.g. plant starch mixed w addition polymer e.g. poly(ethene)
- starch part breaks down making polymer chains smaller and material biodegrades
- concern small pieces of addition polymers cause hazards to the ecosystem
- if only biodegradable polymer used, the new material is bioplastic e.g. plant starch used to make bin bags
- to be fully compostable, plastic must decompose landfill material as quickly as compost would form from grass clippings and other green waste. Only products should be CO2, H2O organic compounds and biomass
What are photodegradable polymers?
- break down chemically using energy w wavelengths similar to light
- they’re addition polymers w bonds within their structure weakened by absorption of light or they have an additive affected by light which weakens bonds in polymer
- once exposed to light, it breaks down (can’t stop process)
- photodegradable polymers in landfill may not be exposed to sufficient light to degrade
What is a bioplastic?
A material made from a renewable source that is biodegradable
