Unit 7 Flashcards
Structural formula
shows the spatial arrangement of all the atoms and bonds in a molecule. AKA displayed formula or graphical formula
Condensed structural formula
enough information is shown to make the structure clear, but most of the actual covalent bonds are omitted. Only important bonds are always shown, such as double and triple bonds
Skeletal formula
simplified displayed formula with:
- All carbon-carbon bonds are represented by lines
- The end of each line and the point where two lines meet is a carbon atom
Stereochemical formula
a formula that attempts to show the relative positions and three-dimensional geometry of atoms and groups of atoms
- Bonds in the plane of the paper are drawn as solid lines
- Bonds coming forward out of the plane (towards you) are drawn as a solid wedge
- Bonds going backward out of the plane (away from you) are drawn as a dashed wedge
Homologous series
A family of similar compounds, having the same functional group, and so similar chemical properties but a different number of carbon atoms
Characteristics of a homologous series
- Each member has the same functional group
- Each member has the same general formula
- Each member has similar chemical properties
- Each member differs by -CH2-
- Members have gradually changing physical properties, for example, boiling point, melting point and density
Physical trend of homologous series
BP increases with increased molecular size
- Each additional CH2 adds more electrons thus increasing strength of LDF leading ot higher BP. Similar trend in other physical properties such as MP, density and viscosity.
Isomers
compounds that have the same molecular formula but a different arrangement of atom
Structural isomers
One group of isomers is the structural isomers. These are compounds that have the same molecular formula but different structural formulae
- Functional group isomerism
- Positional isomerism
- Branched chain isomerism
Functional group isomerism
When different functional groups result in the same molecular formula, functional group isomers arise. These isomers have very different chemical properties as they have different functional groups
- Alkenes and cycloalkanes
- Alcohols and ethers
- Aldehydes and ketones
Positional isomerism
Positional isomers arise from differences in the position of a functional group in each isomer. This means functional group is located on different carbon atoms. Eg:
- Butan-1-ol / Butan-2-ol
- 1-bromobutane / 2-bromobutane
Branched chained isomerism
Compounds have the same molecular formula, but their longest hydrocarbon chain is not the same. This is caused by longest hydrocarbon broken into smaller pieces and some of these smaller pieces are added as side-chains / branches. Eg:
- Pentane / 2,2 - Dimethyl Propane
Polymers
- large molecules built by linking 50 or more smaller molecules called monomers
- Each repeat unit is connected to the adjacent units via covalent bonds
- Some polymers have one unit whilst others contain two or more.
Polymerization example through polyethene
Poly(ethene) is formed by the addition polymerisation of ethene monomers
- many ethene monomers join together due to the carbon carbon double bond breaking
Properties of plastics
- Low weight: loosely packed so will be less dense and lighter than other materials
- Unreactive: saturated compounds because they do not contain double bonds and the main carbon chain is non-polar and will therefore are unreactive
- Water resistant: hydrophobic so they repel water instead of absorbing it
- Strong: made up of many strong covalent bonds between the monomers
- Useful for packaging, construction, clothing and transportation
Primary alcohol oxidation
- oxidized to form aldehydes which can undergo further oxidation to form carboxylic acids
- oxidising agents of alcohols include acidified K2Cr2O7 or acidified KMnO4
Test for primary alcohol oxidation
The oxidation using acidified potassium dichromate(VI) provides the basis for the test for alcohols as the reaction gives a strong colour change from orange to green when changing from alcohol to carboxylic acids
Secondary alcohol oxidation
Secondary alcohols can be oxidised to form ketones only, required sustained heating.
Distillation process for alcohol oxidation test
To produce an aldehyde from a primary alcohol the reaction mixture must be heated
aldehyde product has a lower boiling point than the alcohol thus can be distilled off
Distillation can be carried out using a simple side arm arrangement which acts as an air condenser or the vapours can be made to pass through a condenser
Heating under reflux process for alcohol oxidation test
For reactions that require sustained heating the apparatus has to be modified
To prevent loss of volatile reactants the apparatus includes a condenser in the vertical position which returns components back into the reaction flask
Carboxylic acids reduction
Carboxylic acids are reduced to primary alcohols. This requires heating with LiAlH4 under reflux in dry ether followed by dilute acid
Aldehydes reduction
Aldehydes are reduced to primary alcohols. This can be with LiAlH4 or NaBH4
Ketone reduction
Ketones are reduced to secondary alcohols. This can be with LiAlH4 or NaBH4
Reduction of alkenes
Alkenes are reduced to alkanes in a process called hydrogenation and requires Hydrogen gas (H2) and a nickel catalyst with a temp of 200C and 100kPA
