F322: Basic Concepts And Alkanes Flashcards
Molecular formula
Actual number of atoms of each element in a compound
Empirical formula
Simplest whole number ratio of atoms of each element in a compound
Homologous series
A series of organic compounds with the same functional group but with each successive member differing by a CH2 group. (Thus they have the same general formula, show trends in physical properties eg. Boiling points, and have similar chemical properties)
General formula
Simplest algebraic formula of a homologous series (eg. CnH2n+2 for alkanes)
Structural formula
Minimal detail showing the arrangement of atoms in a molecule
Displayed formula
The relative positioning of atoms and the bonds between them
Skeletal formula
The simplified organic formula, showing only the carbon skeleton with associated functional groups
Functional group
A group of atoms responsible for the characteristic reactions of a compound
Structural isomer
Compounds with the same molecular formula but different structural formula
Stereoisomer
Compounds with the same structural formula but a different arrangement of atoms in space
E/Z isomerism
An example of stereoisomerism, restricted rotation about a C=C bond and two different groups attached to each of the carbon atoms. Z= groups with the higher Mr on the same side.
Cis-Trans isomerism
A special case of E/Z, in which two of the constituent groups are the same. Z (cis) where the groups are on the same side, E (trans) where the groups are on opposite sides.
(Free) Radical
A species with an unpaired electron (diradical- a species with 2 unpaired electrons)
Bond fission
Bond breaking
Homolytic fission
Bond breaks symmetrically, one bonding electron going to each atom, to form two radicals
Heterolytic fission
Bond breaks asymmetrically, both electrons from the bond going to one atom, often forming a cation and an anion
Curly arrow
Movement of an electron pair to show either breaking or making of a covalent bond (should start from from a bond or lone pair of electrons)
Percentage yield
(Actual amount of product obtained/theoretical amount of product expected) X 100. Can be calculated with either moles or mass. Non 100% yields could occur due to: competing side reactions, some product could be lost when it is transferred, a reversable reaction has not had chance to reach equilibrium.
Atom economy
(Molecular mass of desired product/sum of molecular masses of all products) X 100. High atom economy needed in industry to reduce waste and conserve finite resources.
Hydrocarbon
A compound that contains carbon and hydrogen ONLY
Crude oil
Fossil fuel, a mixture of hydrocarbons with different boiling points. A non-renewable resource that takes millions of years to form.
Fractional distillation
A technique for separation on the basis of differences in boiling points
Alkanes
Saturated (single bonds only) hydrocarbons. Tetrahedral shape around each carbon centre with a bond angle of 109.5 degrees.
Trend in boiling points of Alkanes
Boiling points increase with increasing chain length and decrease with increased branching. (More electrons (longer branches) -> stronger and more frequent VDW, more energy needed to break intermolecular forces. More branches -> reduced surface CONTACT area, fewer VDW, less energy needed to break intermolecular forces.)
Complete combustion of hydrocarbons
Burning in plentiful supply of oxygen -> CO2 + H2O (carbon dioxide is a greenhouse gas and increased levels of it in the atmosphere is leading to global warming)
Incomplete combustion of hydrocarbons
Burning in a limited supply of oxygen -> CO (toxic) + H2O (yellow flame, black smoke)
Cracking
Breaking by heat (thermal decomposition) of a long chained alkane into smaller alkanes (which combust more efficiently) and an alkene (used to make polymers and alcohols) any C-C bond can break, giving a mixture of products.
Isomerisation
Converts straight chained hydrocarbons into branched chains (which combust more efficiently)
Reforming
Converts straight chained hydrocarbons into ring compounds (cycloalkanes) + H2
Substitution
When an atom or group of atoms is replaced by another atom or group of atoms
Radical substitution
Alkane + halogen -> halogenoalkane + hydrogen halide.
Mechanism: initiation (homolytic fission by UV), propagation steps, termination.
Condensation polymerisation
Loss of small molecule (usually H2O) from the reacting monomers.
Hydrolysis
Splitting with water
Elimination
1 reactant -> 2 products
