CHAPTER 11-15: Organic Chemistry Flashcards
What are hydrocarbons?
Compound containing carbon and hydrogen atoms
Define what a HOMOLOGOUS SERIES is.
a family of compounds with similar chemical properties whose successive members differ by the addition of a -CH2 group.
Define what a FUNCTIONAL GROUP is.
a part of the organic molecule that is responsible for the molecule’s chemical properties.
What are the 3 groups that hydrocarbons can be classified as?
1) ALIPHATIC - carbons joined in unbranched or branched chains.
2) ALICYLIC - carbons joined in a ring structure.
3) AROMATIC - some/all carbons found in a benzene ring.
What are the 3 homologous series of aliphatics?
1) alkanes
2) alkenes
3) alkynes (triple bonds)
What is an alkyl group?
The side chain group on a branched hydrocarbon
eg. methyl / propyl/ butyl etc.
What prefix is given to alicylic alkanes?
cyclo -
What is the suffix given to:
a) aldehydes
b) ketones
c) carboxylic acids?
a) -al
b) -one
c) -ioc acid
Define what a MOLECULAR formula is.
a molecular formula shows the number and type of atoms of each element present in a molecule.
Define what an EMPIRICAL formula is.
the smallest/simplest whole number ratio of elements in a compound.
Define what a GENERAL formula is.
the simplest algebraic formula for any member of a homologous series.
Define what a DISPLAYED formula is.
A displayed formula shows the relative positioning of all of the atoms in a molecule and the bonds between them.
What is a STRUCTURAL formula?
A formula using the smallest amount of detail to show the arrangement of the atoms in a molecule.
eg. CH3CH2CH2CH3
Define what STRUCTURAL ISOMERS are.
compounds with the same molecular formula but different structural formulae.
What 2 ways are structural isomers formed?
1) same functional group but in different position or different longest chain.
2) different functional group. eg. ketones and aldehydes have same molecular formula.
What is HOMOLYTIC FISSION?
When each atom of a covalent bond gets one of the electrons shared and two radicals are formed.
What is HETEROLYTIC FISSION?
When one of the atoms of a covalent bond gets both of the electrons shared forming a positive ion and a negative ion.
What is a reaction mechanism?
a process to show how a reaction takes place to form the products.
What do ‘curly arrows’ show?
the movement of electron pairs
What happens during an addition reaction?
Two reactants join together to form one product.
What happens during a substitution reaction?
an atom/group of atoms is replaces by another atom/group of atoms.
What happens during an elimination reaction?
The removal of a molecule to form a larger one.
What properties do alkanes have?
- low reactivity
- most stable organic compounds
- saturated hydrocarbons
- a tetrahedral shape around carbon atom - 109.5º
Describe the bonding in alkanes?
each carbon is joined to 4 other atoms by single covalent bonds.
these covalent bonds are called SIGMA bonds - a result of the overlap of 2 orbitals, one from each bonding atom.
Crude oil contains many different alkanes.
By fractional distillation the range of alkanes can be separated, why?
Alkanes have different boiling points.
boiling point increases with increasing chain length.
Why does the boiling point increase with the chain length?
- increased surface area
- more surface contact possible between molecules
- more/stronger london forces
- require more energy to overcome
Why does branching lower the boiling point?
- Fewer surface points of contact between molecules
- branches get in the way
- less london forces
Why do alkanes reactivity?
- C-C bonds are non-polar
- C-C and C-H sigma bonds are strong
- C-H have similiar electronegativity so also non-polar.
When alkanes react with plentiful supply of oxygen what is produced?
(combustion reaction)
CARBON DIOXIDE AND WATER
and heat is given off.
What is the general formula to work out the reaction of a complete combustion reaction?
CxHy + ( x + 0.5y) O2 –> xCO2 + 0.5yH2O
What can be formed instead of carbon dioxide when alkanes are reacted with LIMITED supply of oxygen?
carbon monoxide
carbon (soot)
What is the name of the mechanism when alkanes react with halogens?
RADICAL SUBSTITUION
What are the 3 steps of radical substitution?
1) INITIATION - forming 2 radicals through homolytic fission
2) PROPAGATION
3) TERMINATION - two radicals collide forming a molecule with all electrons paired.
What is required for homolytic fission to take place for a radical substitution?
UV light to provide the energy to initiate the reaction.
Why might there be a mixture of compounds formed from a radical substitution reaction?
Further substitution of the hydrogen atom until all hydrogens are replaced by the radical
Explain the nature of the double bond of alkenes.
3 of the 4 bonds electrons are involved in sigma bonds.
this leaves an electron in the p orbital.
a π bond is formed by the sideways overlapping of the p orbitals above and below the sigma bond between the two carbons.
What prevents the rotation around the double bond of alkenes?
The densities of the π electrons above and below the carbon- carbon bond.
What is the shape/bond around the carbon atom in an alkene? why?
TRIGONAL PLANAR - 120º
3 regions of electron density which repel each other as far as possible
What are stereoisomers?
the same structural formula but a different arrangement of the atoms in space.
What are the 2 requirements of E/Z isomers?
- a carbon-carbon double bond
- different groups attached to each carbon atom of the double bond.
What is the requirement for a cis/trans isomer?
a hydrogen atom attached to each carbon atom of the double bond.
Why are alkenes more reactive than alkanes?
the π bond means the electrons in p-orbital are more exposed and so the π bond is weaker than the sigma bond and is more readily broken.
What are the 3 addition reactions that alkenes undergo and what do they form?
1) HYDROGENATION - an alkane
2) HALOGENATION - a haloalkane
3) HYDRATION - an alcohol
What is added in hydrogenation and under what condition?
a hydrogen atom with a nickel catalyst
What happens during an addition reaction to alkenes?
an addition of a small molecule across the double bond causes the πbond to break and for new bonds to form.
Why does the addition of bromine water to a solution with a c=c present cause the colour to disappear?
bromine is added across the double bond to cause the colour change.
What conditions is hydration occurred in?
addition of STEAM in presence of phosphoric acid/sulfuric acid catalyst
Why does electrophilic addition occur in alkenes?
- the double bond in an alkane is of high electron density
- attracts an electrophile
What is an electrophile?
an electron pair acceptor that is attracted to regions of high electron density.
What type of fission occurs in electrophilic addition to the electrophile?
HETEROLYTIC FISSION
- goes to the more electronegative atom or towards the atom furthest away from double bond when a dipole is induced.
What is the major product?
the more stable carbocation.
Why are tertiary hydrocarbons most stable?
because the more alkyl groups, the more the charge is spread out making the ion more stable.
What are polymers?
extremely large molecules formed from many repeat units (monomers).
How are polymers formed?
unsaturated alkenes undergo addition polymerisation to produce long saturated chains.
What are the environmental positive aspects and problems of polymers?
bad: unbiodegradable
good: low reactivity so suitable for story food, chemicals safely
How can you improve the sustainability of waster polymers?
- recycle: decrease landfill use & use of fossil fuels to create more (but has to be sorted)
- use them to produce heat/energy (as fuel)
- Feedstock recycling - reclaiming the monomers of the waste polymers to use as raw materials for production of new polymers
