Topic 10: Core Organic Chemistry Flashcards
Define saturated
Compounds that contain only single bonds. They have the maximum amount of atoms bonded to each carbon.
Eg. Alkanes
Define unsaturated
Compounds which contain double or triple bonds.
Eg. Alkenes, arenes
(Note: compounds that are unsaturated are highly reactive)
Define aliphatics
Compounds which do not contain a benzene ring (i.e. straight-chained). May be saturated or unsaturated.
Eg. Alkanes, alkenes
Define arenes
Compounds which contain a benzene ring. All unsaturated.
Eg. Benzene, phenol (Phenyl functional group)
Define electrophile
An electron-deficient species that is attracted to parts of molecules that are electron RICH. Attracted to the negative charge. Electrophiles are positive ions or have a partial positive charge.
Define nucleophile
An electron-rich species that is attracted to parts of molecules that are electron DEFICIENT. Attracted to the positive charge. Nucleophiles have a lone pair of electrons or have a negative charge.
Define homolytic fission
When a covalent bond breaks by splitting the shared pair of electrons between the two products. Both atoms get the same number of electrons.
X : X –> X˙ + X˙
Define heterolytic fission
When a covalent bond breaks with both of the shared electrons going to one of the products.
X : X –> X :⁻ + X⁺
What does a double-barbed arrow represent?
↷It represents the motion of an electron pair.
(Drawn from the site of electron availability to the site of electron deficiency)
What does a single-barbed arrow represent?
It represents the motion of a single electron.
(Drawn from the site of electron availability to the site of electron deficiency)
Define homologous series
A group of compounds with similar structural features that can be represented with a general formula.
What do the physical properties of organic compounds depend on?
The physical properties, especially melting and boiling point, depend on the strength of the intermolecular forces. This is relative to the carbon chain length. The longer the carbon chain, the stronger the intermolecular forces therefore the higher the melting and boiling point.
The functional group also tells us about physical properties (eg. polarity/hydrogen bonding).
Define the empirical formula
The simplest whole number ratio of the atoms in a compound. eg. C₂H₆ is CH₃
Define the molecular formula
The actual number of atoms of the different elements in one molecule of the compound.
Give the number of bonds needed for:
Hydrogen
Oxygen
Nitrogen
Carbon
Halogens
Hydrogen - 1
Oxygen - 2
Nitrogen - 3
Carbon - 4
Halogens - 1
Give the general formula for Alkanes
CₙH₂ₙ+₂
Give information about the use of alkanes as fuels
Alkanes are used as fuels because they release significant amounts of energy when they burn (the reaction is highly exothermic).
Complete combustion:
Alkane + excess oxygen —> carbon dioxide + water
Incomplete combustion:
Alkane + limited oxygen —> carbon monoxide + water
Alkane + very limited oxygen —> carbon + water
*The more carbon atoms present the more energy produced (but more oxygen is needed for complete combustion)
What is the environment impact of the use of alkanes as fuels?
Complete combustion:
Carbon dioxide and water are both greenhouse gases and contribute to global warming.
Incomplete combustion:
Carbon monoxide is a toxic gas and can be fatal if produced in a confined space.
Carbon particulates are detrimental to the respiratory system in humans. They also act as catalysts to produce smog in polluted air.
What is the main type of reaction that alkanes undergo?
Free radical substitution (halogenation). This is where a halogen takes the place of a hydrogen atom in the alkane.
There are three steps:
1) Intiation (photochemical homolytic fission)
Occurs in the presence of UV light (this is needed to overcome the strong bonds within the alkane). Two free radicals are produced (i.e. species with an unpaired electron).
2) Propagation (a chain reaction)
Free radicals are used and produced. Starts with 1radical and 1normal molecule and ends with 1radical and 1normal molecule.
3) Termination
Free radicals react together and pair up their electrons.
Cycloalkane reactivity
Smaller cycloalkanes (cyclopropane and cyclobutane) are more reactive because their bond angles are distorted so they are under considerable strain.
Define structural isomers
Structural isomers have the same molecular formula as the compound but a different structural formula (i.e. a different arrangement of atoms).
Give evidence to support the delocalization structure of Benzene (MORE TO COME)
1) Bond lengths
All carbon-carbon bond lengths are of equal length and equal strength. They are intermediate between a single and a double bond.
2) Type of reactivity
Benzene undergoes substitution reactions, rather than addition reactions. (Addition reactions would disrupt the cloud of delocalised electrons and the product would be less stable. Substitution reactions preserve the ring structure).
Give the general formula for alkenes + information on bonds
CₙH₂ₙ
Alkenes have a double bond.
Give the reactions of the alkenes
Alkenes are more reactive than alkanes because the double bond is a site of reactivity. They undergo addition reactions.
1) Hydrogenation
Alkene + H₂ —> Alkane
2) Reaction w a halogen (eg. Br₂, I₂, Cl₂, Fl₂)
Alkene + Cl₂ —> Dihaloalkane
3) Reaction w hydrogen halides
Alkene + HCl —> Haloalkane
* Note the hydrogen halide HF is the least reactive (reactivity of the hydrogen halides increases as you go down G17)
4) Hydration
Alkene + H₂0 —> Alcohol
* Conditions: steam + concentrated sulfuric acid as a catalyst.
