4.1 Basic Concepts and Hydrocarbons Flashcards
What is nomenclature?
A naming system developed by IUPAC for naming compounds in organic chemistry
What is the homologous series?
A series of organic compounds having the same functional group but with each successive member differing my CH2
What are aliphatic hydrocarbons?
Hydrocarbon in which carbon atoms are joined together in either straight (unbranched) chains or branched chains
What are alicyclic hydrocarbons?
Hydrocarbon in which the carbon atoms are joined together in a ring structure but are not aromatic
What are aromatic hydrocarbons?
Hydrocarbons in which there is at least one benzene ring in the structure
What are alkanes?
- The simplest homologous series
- Aliphatic saturated hydrocarbons
- Only carbon and hydrogen joined by single covalent bonds
Name the first ten alkanes
- Methane
- Ethane
- Propane
- Butane
- Pentane
- Hexane
- Heptane
- Octane
- Nonane
- Decane
What is the general formula for alkanes?
CnH2n+2
What is the general formula for alkenes?
CnH2n
State the three rules you name an organic compound by
stem, suffix and prefix
What is the stem?
the main part of the name; generated by identifying the longest carbon chain or parent chain
What is the suffix?
the end of the name; identifies the most important functional group
What is the prefix?
the front part of the name; identifies the other functional groups and the carbon atoms they are attached to
What happens when you remove a hydrogen atom from an alkane?
An alkyl group is formed
What are the rules in the stem of naming compounds?
- Look for the longest chain of carbon atoms containing the functional group
- the carbon atoms must be in a continuous row
- use prefixes
- ending tells you what type of carbon structure you have; alkanes end in ANE
What are the rules in naming the side-chain in organic compounds?
- carbon-based substituents are named before the chain name
- they have the prefix -yl added to the basic stem
- number the principal chain from one end so that the side chain is attached to a carbon atom with the lowest possible number
What rules apply when there is more than one side-chain
- side chain names appear in alphabetical order
- number the principal chain from one end to give the lowest numbers
- each side chain is given its own number
- if identical side-chains appear more than once, prefixes with di, tri, tertra etc
- numbers separated from names by a HYPHEN
- numbers separated from numbers by a COMMA
What is a functional group?
A group of atoms responsible for the characteristic reactions of a compound
What can a functional group consist of?
- one atom
- a group of atoms
- multiple bonds between carbon atoms
What are saturated compounds?
Saturated compounds only have single bonds
What is a general formula?
the simplest algebraic formula for a homologous series
What is the general formula for alcohols?
CnH2n+1OH
What is a displayed formula?
Shows the relative positions of all the atoms in a molecule and the bonds between them
What is the structural formula?
Provides the minimum detail for the arrangement of atoms in a molecule
What is the empirical formula?
Shows the smallest whole-number ratio of atoms of the elements in the compound
What are the steps to work out the empirical formula?
Step 1: Change the percentages to masses
Step 2: Calculate the number of moles of each element using n=m/Mr
Step 3: Divide by the smallest number of moles
Step 4: Change the ratio to whole numbers
Step 5: Write the formula
What is the molecular formula?
Shows the numbers and types of atoms in a compound
How can you work out the molecular formula?
Step 1: Calculate the relative empirical mass using the empirical formula
Step 2: Divide the relative molecular mass by the empirical formula mass
Step 3: Multiply each atom in the empirical formula by the number calculated in step 2 and write the molecular formula
What is a skeletal formula?
The briefest way of representing organic molecules. Lines are used to indicate alkyl chains, and every corner represents a carbon atom
What are unsaturated hydrocarbons?
Unsaturated hydrocarbons are organic compounds that contain only carbon and hydrogen, and usually, have at least one C=C unit representing a double bond
What are aromatic hydrocarbons?
- Have a 6-carbon ring
- Molecular formula C6H6
- Very stable structure because the electrons are shared across all the carbon atoms
What are the functional groups for alcohols and carboxylic acids?
Alcohols: -OH
Carboxylic acids: -COOH
What are isomers?
Isomers are compounds which have the same molecular formula but different arrangements of their atoms
What are structural isomers?
Structural isomers are compounds with the same molecular formula but different structural formula
What are the three ways structural isomers can occur?
- The alkyl groups are in different places
- The functional group can be bonded to different parts of the parent chain
- The functional group could be different
What are stereoisomers?
Stereoisomers are organic compounds which have the same molecular formula and structural formula but a different arrangement of atoms in space
What is Z/E isomerism?
A type of stereoisomerism. An organic molecule must have a C=C double bond and both carbons must be attached to different groups
How do you identify Z/E isomers using the Cahn-Ingold-Prelog rules?
- Locate the C=C double bond in the molecule and redraw it to show the substituents
- Focus on one carbon atom and assign the priority of each substituent based on its relative atomic mass- the highest is given the highest priority. Then assign the priority of the second carbon atom
- If the highest priority groups are on the same side of the C=C double bond, then the isomer is Z. If they are on different sides of the C=C double bond then the isomer is E
What is cis-trans isomerism?
A special type of Z/E isomerism where two substituents on each carbon atom are the same. The E isomer is also a trans isomer and the Z isomer is also a cis isomer
What is a reaction mechanism?
Model that shows the movement of electron pairs during a reason
What is homolytic fission?
When a covalent bond breaks and each electron goes to a different bonded atom
Also known was equal splitting
What does homolytic fission generate ?
Two highly reactive neutral species called radicals
What are radicals?
Highly reactive species with one or more unpaired electrons
What is heterolytic fission?
Heterolytic fission occurs when a covalent bond breaks and both electrons go to one of the bonded atoms
Also known as unequal splitting
What does heterolytic fission produce?
A positive ion (cation) and negative ion (anion) being formed
How do covalent bonds form?
When two radicals or two oppositely charged ions collide, a new bond is formed
Why are carbocations very reactive intermediates?
They are unstable
What are alkanes?
- Form a homologous series
- Hydrocarbons (contain only hydrogen and oxygen atoms)
Are alkanes saturated or unsaturated?
Saturated
What is the general formula for alkanes?
CnH2n+2
What is the bonding like in alkanes?
Every carbon atom has a tetrahedral shape with a bond angle of 109.5 degrees
Are alkane molecules polar?
The electronegativity values for hydrogen and carbon are very similar so alkanes are non-polar and without any significant permanent dipoles- only instantaneous dipoles
How does carbon chain-length effect the boiling point of alkanes?
As an alkane chain gets longer, the molecules have more surface area contacts between adjacent molecules. This increases the number of induced dipole-dipole forces, so more energy is needed to overcome the intermolecular attraction in order that the alkane can change state
How does branching effect the boiling point of alkanes?
The more branched a compound is, the fewer surface area interactions there are between molecules- because the molecules cannot fit together as neatly.
Branched chains have fewer induced dipole-dipole attractions compared to the straight-chain isomer so branched molecules have a lower boiling point than the equivalent straight-chain isomer
Are alkanes reactive?
Alkanes have a low reactivity with many reagents
Why are alkanes unreactive?
- All the covalent bonds in alkane molecules have high bond enthalpies so a large amount of energy is required to break them
- The carbon-hydrogen sigma bonds have very low polarity because the electronegativities of carbon and hydrogen are almost the same
What are the two types of combustion?
Complete and incomplete
What is produced in complete combustion?
Carbon dioxide and water
What is produced in incomplete combustion?
Carbon particles (soot), water, carbon dioxide and carbon monoxide(CO)
What is a radical substitution?
An organic mechanism involving radicals when one or more atoms get exchanged
Name the three stages of radical substitution
- Initiation
- Propagation
- Termination
What are the reagents for homolytic free radical substitution?
a halogen and alkane e.g. chlorine and methane
What are the conditions needed for homolytic free radical substitution?
UV lights or sunlight
What happens at initiation?
the formation of radicals
What happens at propagation?
radicals are used and then re-generated
What happens at termination?
radicals removed to form a stable product
What are alkenes?
- Form a homologous series
- Are hydrocarbons (contain only carbon and hydrogen atoms)
Are alkenes saturated or unsaturated?
Unsaturated, containing at least one C=C
What is the general formula for alkenes?
CnH2n
What are the C-H bonds in alkenes?
Sigma bonds.
What does a double covalent bond have?
Two sections involving the overlap of electron clouds
What is a sigma ( σ ) bond?
A σ bond is formed between two carbon atoms using the direct overlap of the electron clouds of the two atoms
What is a pi (π) bond?
A π bond is formed by the electrons in the adjacent p-orbitals overlapping above and below the carbon atoms
When can a pi bond be formed?
Only after a σ bond has been formed
What is the structure of alkenes?
-each carbon atom in the molecule has three areas of electron density: two separate covalent bonds between the carbon atoms and hydrogen atoms and the covalent bonds between two carbon atoms
Each of these electron densities repel by the same amount forming bond angles of 120 degrees, which results in a trigonal planar shape
What can be formed if an alkene has different alkyl groups attached to both carbon atoms in the double bond?
Stereoisomers
What is formed when there are two identical substituent groups are attached to each carbon atom?
A special case of isomerism called cis-trans isomerism
What is homolytic fission?
When a covalent bond breaks and each electron goes to a different bonded atom
What does homolytic fission produce?
Two highly reactive, neutral species called radicals. Radicals have one or more unpaired electrons which are shown as dots
What is heterolytic fission?
When a covalent bond breaks and both electrons go to one of the bonded atoms
What does heterolytic fission result in?
A positive and negative ion
What are alkanes?
- Hydrocarbons (contain 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 kind of bonding is present in alkanes?
Each covalent bond has direct overlap of the electron clouds from each atom making a sigma bond. Therefore C-C and C-H are examples of sigma bonds
What is the shape of an alkane?
Every carbon atom has a tetrahedral shape with a bond angle of 109.5 degrees
Are alkanes polar?
The electronegativity values of carbon and hydrogen are very similar therefore alkane molecules are non polar and without any significant dipoles. However they do have weak induced dipole-dipole interactions
How does carbon-chain length affect boiling point of alkanes?
As the carbon-chain increases the relative molecular mass increases. Larger molecules have more surface area contact between adjacent molecules. This increases the amount of induced dipole-dipole forces. More energy is needed to overcome the intermolecular attraction therefore the boiling point increases
How does branching affect boiling point of alkanes?
The more branched a compound is, the fewer surface area interactions there are between molecules because they can’t fit together as neatly. Branched molecules have fewer induced dipole-dipole interactions compared to straight chains so the boiling point of branched compounds is lower
Why do alkanes have low reactivity (2 reasons)?
- All the covalent bonds have high bond enthalpies so a large amount of energy is needed to break them
- The carbon-hydrogen sigma bonds have very low polarity because the electronegativities of carbon and hydrogen are almost the same
Why do alkanes undergo combustion?
So that they can be used as fuels- to transfer their stored chemical energy into usable thermal energy
When does an alkane undergo complete combustion and what are the products?
- When there is plentiful supply of air
- Clean, blue flame
- Only carbon dioxide and water are produced
When does an alkane undergo incomplete combustion?
- When there is a limited supply of air
- Dirty yellow flame
- Products are water, carbon dioxide and carbon monoxide (colourless, odourless and toxic gas)
What is radical substitution?
When alkanes react with both chlorine and bromine in the presence of UV light to form halogenated organic compounds. Halogenation happens by homolytic fission of the halogen molecule, forming radicals
What are the three steps of the radical substitution mechanism?
- Initiation- formation of radicals
- Propagation- two repeated steps that build up the desired product in a side-reaction
- Termination- two radicals collide and make a stable product
What are the conditions needed for initiation?
UV light or temperatures of about 300 degrees
What happens in propagation? (2 steps)
Step 1: An alkyl radical is generated and HX (where X is a halogen)
Step 2: The desired product is generated and the halogen radical is regenerated
What happens at termination?
A mixture of products is produced by the random collisions between radicals
What are alkenes?
- are hydrocarbons containing only hydrogen and carbon atoms
- are unsaturated containing at least one C=C bond
- have the general formula Cn H2n
- have a graduation in physical properties
- have similar chemical properties
What is the bonding like in alkenes?
- The C-H bonds are sigma bonds
- The C=C bond has two sections involving the overlap of electron clouds
- The sigma bond is formed between two carbon atoms using the overlap of electron clouds
- The pi bond is formed by the electrons in the adjacent p-orbitals overlapping above and below the carbon atoms
- The pi bond holds the atoms in position by restricting rotation around the double bond
What is the shape of alkene molecules?
There are three areas of electron density:
- two separate covalent bonds between the carbon atoms and two different hydrogen atoms- these are sigma bonds
- the covalent bonds between the two carbon atoms, made from the sigma and pi bond
These form bond angles of 120 degrees which result in a trigonal planar shape
How are stereoisomers formed?
If an alkene has different alkyl groups attached to both carbon atoms of the double bond
When is a cis-trans isomer formed?
When two identical substituent groups are attached to each carbon atom
Are alkenes reactive?
Alkenes are more reactive than alkanes because of the double bond
Why are alkenes more reactive than alkanes?
The pi bond needs less energy to undergo homolytic fission and is weaker than the sigma bond so breaks first and reacts, leaving the sigma bond between the two carbon atoms
What are electrophiles?
Electrophiles are species that are electron-pair acceptors, like positive ions and molecules with a delta positive region of charge
What happens in a general addition reaction for alkenes?
The pi bond breaks and a small molecule is added across the two carbon atoms to make a saturated organic product
What is hydrogenation and what are the conditions needed?
- Hydrogenation is when hydrogen is added across the C=C bond
- The conditions needed is a temperature of 150 degrees and a nickel catalyst
What does hydrogenation result in?
Saturated alkane
What is halogenation?
A halogen is added across the C=C bond
What does halogenation result in?
A saturated alkene and a dihaloalkane is produced
What can halogenation be used to test for?
Saturation- when a bromine is mixed with a saturated compound there is no reaction but when it is mixed with an unsaturated compound it decolourises
What is hydration and what conditions are needed?
- Addition of water
- Conditions involve high temperatures and pressures with a phosphoric acid catalyst
What does hydration result in?
Formation of an alcohol
What is addition of hydrogen halides?
When a hydrogen halide is added across the C=C bond
What does addition of hydrogen halides produce?
Haloalkanes- saturated organic compounds. At least one hydrogen atom is replaced by a halogen atom
What happens when a hydrogen halide is added to an unsymmetrical alkene?
There are two possible products
What is Markonikoff’s rule?
This states that when H-X is added to an unsymmetrical alkene, the hydrogen becomes attached to the carbon with the most hydrogen atoms. Carbocations that have alkyl groups attached are more stable than those with hydrogen atoms attached
What occurs during addition polymerisation?
Monomers have their pi bonds broke. The electrons from each pi bond make a sigma bond with a neighbouring carbon atom on a different monomer. This connects monomers chemically, generating a saturated polymer with long carbon chains
What are polymers?
Polymers are macromolecules made from small repeating units. They can be millions of atoms long
What are the 4 steps necessary to generate the repeating unit of a polymer from its monomer?
Step 1: draw the monomer structure so that the C=C bond is the focus of the diagram
Step 2: draw square brackets around the monomer
Step 3: change the C=C bond to C-C and draw two lines extending from each C atom through the square brackets
Step 4: add a subscript ‘n’
Name the 6 different ways plastics are disposed of
- Landfill
- Combustion
- Combustion with electrical generation
- Reusing
- Recycling
- Using them as organic feedstock
How are plastics disposed of in landfill?
Large holes are dug in the landscape. Rubbish is then put in the holes and compacted.
How are plastics disposed of using combustion? Why is this bad?
- Plastics are mainly organic and can be burnt
- They contain large amounts of carbon so produce carbon dioxide (a greenhouse gas) when burned
- Plastics can be burnt in power stations and the chemical energy transferred can be used to drive turbines and generate electricity
How can plastics be reused and recycled?
- Some plastics can be reused for the same function many times, for example, a water bottle
- To be recycled, plastics are cleaned, melted down and reshaped into new products
How are plastics used as organic feedstock?
A series of chemical reactions can be used to break the plastic polymers up into small organic molecules which allows the recovered chemicals to be used in other industrial reactions
What are biodegradable polymers?
Biodegradable polymers can be attacked by microorganisms and environmental conditions so that they break down chemically into harmless substances
How can addition polymers be made biodegradable?
If you mix a biodegradable polymer like starch in with an addition polymer, the starch breaks down making the polymer chains smaller and the material biodegrades
What are photodegradable polymers?
Photodegradable plastics break down chemically using energy with wavelengths similar to light. Their bonds are either weakened by absorption of light or they have an additive that is affected by light which then weakens the bonds.
What is a bioplastic?
A material made from a renewable source that is biodegradable
