Basic Concepts and Hydorcarbons Flashcards
Why do we name organic compounds
scientists communicate in many different languages therefore it is important that each chemical substance has its own unique name, avoids ambiguity
the IUPAC developed a naming system for organic chemicals called nomenclature
what are the first 4 alkanes called
Methane
Ethane
Propane
Butane
What are the three rules for naming branched alkanes
stem = the main part of the name generated by identifying the longest carbon chain or parent chain suffix = the end of the name identifying the most important functional group prefix= the front part of the name identifying the other functional groups and the carbon atoms there attracted to
What happens when you remove an hydrogen atom from an alkane
an akyl group is formed
name the 10 alkyl groups and there formula
methyl CH3 ethyl C2H5 propyl C3H7 butyl C4H9 pentyl C5H11 hexyl C6H13 heptyl C7H15 octyl C8H17 nonyl C9H19 decly C10H21
What is the prefix of an alcohol
Hydroxy
what is the suffix of a carboxylic acid
oic
what is the suffix and functional group of a ketone
one
c-co-c
what is the formula for alkanes
CnH2n+2
what is the formula for alkenes
CnH2n
what is the formula of alcohols
CnH2n+1OH
what are cyclic compounds
they are saturated hydrocarbons
what do aromatic compounds always have
6 carbon rings and the molecular formula C6H6
why are aromatic compounds more stable
they are stable as all electrons are shared out across all carbon atoms therefore they are rarely involved in a chemical reaction
in a carboxylic acid where is the double bond
between carbon atoms and oxygen atoms
What is covalent bond fission
this is during the first stage of a chemical reaction when the activation energy effects the covalent bond causing them to break this is describe as undergoing fission
When does homolytic fission occur
this occurs when a covalent bond breaks and each electron goes to a different bonded atom,
this generates two highly reactive neutral species called radicals,
What do radicals have
they have one or more unpaired electrons which are shown as dots
what does UV light do
causes the covalent bond to break as it breaks the weaker pie bonds then the sigma bonds
When does heterolytic fission occur
this occurs when a covalent bond breaks and both electrons go to one of the bonded atom this results in a a positive ion and negative ion being formed
What is covalent bond formation
this is when two radicals or two oppositely charged ions collide and a new bond is formed
What are carboncations properties
very reactive intermediates as they are very unstable
what do alkanes have
- hydorcarbons containing only hydrogen and carbon atoms
- saturated containing only single covalent bonds
- have the general formula CnH2n+2
- have a graduation in physical properties
- have similar chemical properties
What are the bonding in alkanes
tetrahedral shape with a bond angle of 109.5, 4 bonding pairs
What are alkanes a example of in terms of bonding
they are an example of sigma bonds, each covalent bond has a direct overlap of electron clouds between each atom making a sigma bond
Describe the boiling points of alkanes
- as chain length increases the relative molecular mass increases,
- large molecules have more surface area contact with adjacent molecules this increases the number of induced dipole-dipole forces therefore more energy is needed to overcome the intermolecular attraction in order to break the chain therefore boiling points increase
What do chains do to the boiling point of alkanes
the more branched a compound is the fewer surface area interactions there are between adjacent moleucles as they cannot fit together neatly, therefore branched molecules have fewer dipole dipole attractions and less energy is needed to break the intermolecular attraction and the boiling point decreases
- reduces ability of molecules to pack closely together
Why do alkanes have low reactivity
- all the covalent bonds in alkane molecules have high bond enthalpies therefore a large amount of energy is needed to break the bonds
- the carbon-hydrogen sigma bonds have a very low polarity because of the electronegativity’s of carbon and hydrogen are almost the same
What is combustion
Combustion is a rapid oxidation reaction which combines oxygen from the air with another substance
What is complete combustion
this happens when there is a plentiful of air therefore enough oxygen to undergo complete combustion
- makes clean blue flame and transfers the maximum amount of thermal energy because it fully oxidises carbon and hydrogen
- produces water and carbon dioxide
what is incomplete combustion
this is when there is not enough oxygen to react completely with the alkane
- produces water and carbon monoxide this can be dangerous
complete combustion equation
CnH2n+2 + (3n+1/2)02 = nCO2 + (n+1)H20
incomplete combustion equation
CnH2n+2 + (n+0.5)02 = (n+1)H20 + nCO
What do alkanes react with to from halogenated organic compounds (Halogenation)
they react with bromine and chlorine in the presence of UV light,
How does halogenation works and what happens in it
Happens by homolytic fission of the halogen molecules which form radicals
- A hydrogen atom in the alkane is substituted by a halogen atom, if the reaction conditions are maintained the substitutions can continue until all the hydrogen atoms in the original alkane have been replaced by halogen atoms
what is the three stages of radical substitution mechanism
- initiation
- propagation
- termination
Disadvantages of radical substitution
- unpredictable
- difficult to control
- mixture of products is formed which has to be separate by processes of fractional distillation of chromatography
- radicals are highly reactive
- multiple substitutions
Describe steps of radical substitution
- initiation - UV light breaks the covalent bond by heating it a radical has been generated
- propagation - radical reacts with the alkane and produces an alkyl radical and hydrogenradcial, the the desired product is created from the alkyl radical and orginal cl2 or br2, regenerates the chlorine radical
- termination -radicals react with each other forming other elements and the product itself
Why does radical substitutions chain reactions
because the radicals keep getting produced and used
how is the carboxyl group and ester group represented in structural formulae
COOH
COO
Draw radical subsitiution steps for chlorine and bromine
DRAW IT
what does aliphatic mean
- this is a molecule that is made up of hydrogen atoms and carbon atoms which may contain rings and branches but is not aromatic
