Module 4.1 Basic concepts and hydrocarbons Flashcards
Homologous series
A series of organic compounds having the same functional group but with each successive member differing by CH2
Functional group
Part of a molecule which determines how it reacts
How do we name a alkane?
- add the prefix (first part of name) depending on how many carbon atoms
- then add -‘ane’ to the end
How do we name a alkene ?
- add the prefix determined my how many carbon atoms there are
- number carbon atoms from the side where the double c=c bond will be the lowest
- add the c=c number
- end with ‘ene’
How do we name branched chained hydrocarbons ?
- identify the longest carbon atoms
- number the carbon chain so the functional group sits on the lowest carbon number possible
- look at the side groups and determine which akyl group there are in and what carbon the sit on
- if there is more than one identical functionial group/side chain put di-2, tri-3 tetra-4
- name by the number on side group and alkyl name, the carbon chain name, carbon number the functional group is on and the suffix.
General formula
The simplest algerbraic formula of a member of a homologous series
Alkane general formula
CnH2n+2
Alkene general formula
CnH2n
Alcohols general formula
CnH2n+1OH
Structual formula
The minimal detail that shows the arrangement of atoms in a molecule without showing bonds
Sketetal formula
Shows just a carbon skeleton and functional groups. Hydrogen is not shown
Display formula
- the relative positioning of atoms and bonds between them
Prefix’s naming molecules
1- meth 2-eth 3-prop 4-But 5-pent 6-Hex 7-hept 8-oct 9-non 10-dec
Alkyl groups
Hydrocarbon branches with the general formula CnH2n+1
Aromatic compounds
- contains a benzene ring. They may have functional groups and alkyl groups coming from this
Aliphatic compounds
- straight, branched chains or non aromatic rings with or without side chains
Alycyclic compounds
- a aliphatic compound arranged in non-aromatic rings with or without side chains
Unsaturated compound
- multiple carbon-carbon bonds
Saturated compounds
- single carbon-carbon bond
Structural isomers
- conpounds with the same molecular formula but differnt structural formulae. There are 3 types: chain, positional and functional group
Chain isomerism
- compounds with the same molecular formula but different arrangement of the carbon skeleton
Positional isomerism
- compounds with the same molecular formula but different position of functional group on the carbon skeleton
Functional group isomerism
-compounds with the same molecular formula but different functional group
Homolytic fission
Each bonding atoms reveives one electron from the bonded pair,
forming two radical
Heterolytic fisson
One bonding atom receiving both electrons from the bonded pair
Radicals
A species with an unpaired electron
What does the dot represent in a reaction mechanism?
- radicals
What does a curly arrow represent?
The movement of electrons
Properties of alkanes
- saturated hydrocarbon. Each carbon is bonded 4 times
- form a tetrahedral shape (109.5 degrees) because all the bonds repel each other equally.
- larger molecules (longer carbon chain) have more induced dipole-dipole forces due to having a larger electron cloud and more surface contact. so a higher boiling point.
- branched molecules have fewer induced dipole attraction due to fewer surface area interaction between molecules so have a lower boing point.
Why do alkanes have a low reactivity with many reagents?
- all covalent bonds in alkanes have high bond enthalpies
- the carbon-hydrogen sigma bonds have very low polarity as the electronegatibites of crabon and hydrogen are almost the same.
Complete combustion of alkanes
- burns completely in oxygen wgen there is a plentiful supply forming CO2 and H20.
Incomplete combustion of alkanes
- burns with a limited supply of oxygen producing carbon monoxide( CO) and carbon particles (soot)
3 main stages of radical substitution ( alkanes react with chlorine and bromine forming halogenated organic compound)
- inititation: radicals are produced normally using visible or UV light (photochemical reactions)
- propagation: when a radical reacts woth a non-radical molecules forming new radicals which go on to react with other non- radicaks.
- termination: two radicals react to make a stable non-radical molecule (chloromethane) ends reaction
Limitations of radical substitution
- forms a mixture of organic products. and side products ( multiple substitutions) therefore there is a low atom economy
Adding excess of the reactant can reduce the amount of substitutions. There is a greater chance of radical reacting with the product than another substance
- isomers are formed as free radical substitution can occur abywhere on a hydrocarbon chain
steroisomerism
molecules with the molecular formula but different arrangement of atoms in space
cis-trans isomerism
- naming isomer system
- carbon atoms on each side of the double bond must be bonded to 2 different groups and at least one of theses groups must be the same on both sides of the carbons on the double bond.
- find the group the same on both sides if the group are on the same side it is a CIS isomer
- if the group are on opposite sides its a TRANS isomer
using CIP rules to determine E/Z isomers
- assign priority to the highest atomic number group on both sides of the carbon atoms
- if the priority groups are on the same side its a Z isomer and on different sides its a Z isomer
Properties of alkenes
- trigonal planar shape (120 degree) The three bonding pair of electrons are in the plane of the molecule and repel each other equally
- stereoisomerism
- very reactive due to the Pi bonds having a high electron density and low bond enthaplys
E/Z isomerism
An example of steroisomerism, in terms of restricted rotation about a double bond and the reuirement for two different groups to be attached to each carbon atom of the C=C group
Cis-trans isomerism
A special case of E/Z isomerism in which two of the substituent groups attached to each carbon atom of the C=C group are the same.
Electrophile
An electron pair acceptir
The use of bromine to detect the presence of a double C=C bond
- Bromine is polarised as the electrons in the double repel the electrons in Br2 moving them to one side creating a dipole
- an electron pair in the double bond is attracted to the slighly positive bromine and form a bond. This breaks the Br-Br (heterlytic fission)
- a carbon cation intermediate is formed and Br is attracted to the C+
- this forms colourless dibromoethene
Hydrogenation
-hydrogen is added across a C=C bond. At 150 degree temp with a nickel catalyst. This saturated the alkene forming a alkane.
Hydrogen halides to form haloalkanes
- H-X is permanently polarised e.g HBR
- heterlytic fission breaks the bonds between HBR
- a carbon intermediate is formed and the Br- is attrated to the C+
addition reaction with steam
- addition reaction between gaseous alkene and steam. Used to make alcohols.
- conditions involve high temperatures and high pressures with a phosphoric acid catalyst
- reversible reaction with a inital reaction yield of only 5%. Any unreacted alkene is recycled through and an overall yield at 90-95% can be obtained overall
Markownikoffs rule
when H-X is added to an unsymmetrical alkene, the hydrogen becomes attached to the carbon with that is most stable than those with hydrogen atoms attached
reactions of alkenes
- very reactive due tom the pi bond which have a high electron density
- then Pi electrons are on the outside of the double bond this makes it easier to break as they are more exposed
- because the double bond breaks it is possible to add atoms/groups to the alkene
- undergo addition reactions with:
- hydrogen
- halogens
- hydrogen halides
- steam
combustion of energy production
- plastic can be burnt in power stations. the chemical energy transferred can be used to drive turbines and generate electricity.
organic feedstock
- waste polymers are broken down by chemical and thermal processes into monomers. Which can be used as the raw materials in the production of new polymers and other organic chemicals.
- benefit is it works well with unsorted and unwashed polymers
the benefits of biodegradable and photodegradable polymers
- biodegradable polymers can be broken down over time by microorganisms
- photodegradable polymers contain bonds that are weakened by absorbing light/visible radiation breaking down the polymer,.
- compostable polymers are commonly plant based .they degrade naturally leaving no harmful residues.
- bioplastics are polymers that are made from plant starch
