4.1 basic concepts and hydrocarbons Flashcards
general formula
Simplest algebraic formula of a member of a homologous series
Alkanes- CnH2n+2 Alkenes- CnH2n
homologous series
Series of organic compounds having the same functional group but with each successive member different by CH2
functional group
Group of atoms responsible for the characteristic reactions of a
compound
E.g.- -Cl, -OH
functional group isomerism
Position of atoms cause a different functional group
structural isomerism
Compounds with the same molecular formula but a different structural formula
chain isomerism
Isomers have different chain length caused by branching
positional isomerism
The position of a functional group differs along a chain
isomerism
Aliphatic isomers –
compound arranged in a non-aromatic rings. With or without branching chains
Aromatic isomers-
a compound containing a benzene ring
Structural isomers- Compounds with the same molecular formula but a different structural formula
saturated
single carbon–carbon bonds only) and unsaturated (the presence of multiple carbon–carbon bonds, including C=C, C multiple / and aromatc rings
saturated
single carbon–carbon bonds only) and unsaturated (the presence of multiple carbon–carbon bonds, including C=C, C multiple / and aromatc rings
covalent bond fission- homolytic
in terms of each bonding atom receiving one electron from the bonded pair, forming two radicals
covalent bond fission- heterolytic fission
in terms of one bonding atom receiving both electrons from the bonded pair
radicals
a species with an unpaired electron
‘dots’ represent species that are radicals in mechanisms
Dots, •, are required in all instances where there is a single unpaired electron (e.g. Cl• and CH3•).
Dots are not required for species that are diradicals (e.g. O). (h)
curly arrow
Is described as the movement of an electron pair, showing either heterolytic fission or formation of a covalent bond
alkanes
saturated hydrocarbons containing single C–C and C–H bonds as σ-bonds (overlap of orbitals directly between the bonding atoms) which allow free rotation of the σ-bond
Is non-polar, so has only London dispersion forces
Is only soluble in non-polar solvents.
The properties depend on chain length and branching
More points of contact mean there are more intermolecular forces
boiling point of alkanes
Increases with the length of chain
Packing describes how closely they can get together and branching in alkanes cause them to not pack as close together, which lowers the boiling point
alkanes and reactivity
Low because of:
Low polarity
High bond enthalpy
A very slight dipole but still non-polar
combustion of alkanes
Is exothermic- addition of oxygen Complete when there is excess oxygen CH4 + 2O2 → CO2 + 2H2O Incomplete when there is limited oxygen CH4 + O2 → C + 2H2O CH4 + 2O2 → CO + 2H2O Complete calculations are often balanced so that the fuel is given as 1 mol, allowing oxygen to have halves
oxidation of alkanes
Combustion of methane CH4 + 1 ½ O2 → CO + 2H2O CH4 + O2 → C + 2H2O CH4 + 2O2 → CO2 + 2H2O Carbon is reduced and hydrogen is oxidised
radical substitution
An unbonded electron in an atom/molecule is highly reactive
Formed by homolytic fission ( homolysis)
Homolytic- each atom in a bond takes 1 of the shared electron
Fission- splitting of the covalent bond .
UV radiation has enough energy to split a covalent bond within bonds to form radicals.
∙ represents an unpaired electron
what are the 3 stages to radical substitution
Initiation- radical formation
Propagation- formation of product and new radicals
Termination- reaction ends as radical is removed
alkenes
unsaturated hydrocarbons containing a C=C bond comprising a π-bond (sideways overlap of adjacent p-orbitals above and below the bonding C atoms) and a σ-bond (overlap of orbitals directly between the bonding atoms)
stereoisomerism
Occurs in compounds with the same structural formula but different arrangement in space
The pi- bond in alkenes restrict the rotation of the molecule potentially causing E/Z isomerism
Sigma-bonds can rotate so stereoisomerism cant occur in alkanes
E/Z stereoisomerism
Can only occur if:
There’s a C=C bond
Each carbon is bonded to a different atom/group
E-isomerism- priority groups are on opposite sides
Z-isomerism- priority groups are on the same side