C11-. Organic Chemistry I Flashcards
What is a functional group defined as?
An atom/group of atoms responsible for the typical chemical properties/reactions of a molecule.
What is a homologous series?
A series of molecules with the same functional group but different numbers -CH2 groups. These all have a general formula.
What is the functional group of an alkene?
C=C with double bond
What is the functional group of a halogenoalkane?
R-X where X could be any halogen
What is the functional group of an alcohol?
-C-OH
What is the functional group of an aldehyde?
-COH with C=O
What is the functional group of a carboxylic acid?
-COOH with C=O
What is the functional group of a ketone?
C=O
What is the functional group of an ester?
-COO with O=C and C-O
Describe the naming convention for organic compounds, set by IUPAC.
- Prefixes - position and identity of side-chain substituents
- Stem: no. of carbon atoms in longest chain
- Suffix: functional group
How do we number functional group and side chains on a main carbon chain?
The functional group should be designated the lowest number possible.
When multiple substituent groups are present, how are they ordered?
Alphabetically, i.e. ethyl comes before methyl. This does not include prefixes like di-, tri-, tetra-.
Define empirical formula.
The simplest whole number ratio of atoms of each element in a compound.
Define structural formula.
Uses the smallest amount of detail necessary to show the arrangement of atoms in a molecule.
Define displayed formula.
Shows the relative positioning of all atoms in an molecule, and the bonding present between them.
Define skeletal formula.
A simplified organic formula, where hydrogen and carbon labels, and bonds to hydrogens atoms, are removed, leaving a carbon skeleton and functional groups.
What is structural isomerism?
When two or more molecules have the same molecular formula, yet have different structural formulae.
Define positional isomerism, and give examples of this with the context of C6H12.
- This occurs when the functional group occupies different positions along the chain.
- So this could be exemplified by C6H12, which could represent hex-1-ene, hex-2-ene, or even cyclohexane.
What is functional group isomerism?
This is when the function groups of organic molecules are different for the same molecular formula.
What is chain isomerism?
This occurs where the chain attached to the functional group changes in some way for a given molecular formula, such as hex-1-energy and 4-methylpent-1-ene.
Why are alkanes generally quite unreactive?
- Everything is covalently bonded. These bonds are not readily broken.
- Alkanes are non-polar molecules. This is because C-C bonds and C-H bonds are both considered non polar.
What are the products of the complete combustion of an alkane?
Carbon dioxide and water.
Give the causes and products of incomplete combustion of alkanes.
- If an insufficient oxygen supply is available, alkanes incompletely combust.
- This results in the production of carbon monoxide and soot.
What are the three types of species that can attack a molecule?
- Electrophile
- Nucleophile
- Free radical
What is a reaction mechanism?
This provides information about how a reaction takes place, i.e. what actually happens and the attacking species.
Define electrophile.
An electron pair acceptor. This means it is attracted to an electron rich centre, so it accepts a pair of electrons to form a new bond.
Define nucleophile.
An electron pair donor. This means it is attracted to an electron deficient centre, so it donates a pair of electrons to form a new bond.
Define free radical.
An atom/group of atoms with a single unpaired electron. These are highly reactive for this reason.
In what two ways can covalent bonds be broken?
- Homolytic fission
- Heterolytic fission
What is homolytic fission?
A covalent bond is split such that each resulting atom gains one of the electrons from the bonded pair. This results in the formation of 2 free radicals.
What is heterolytic fission?
A covalent bond is split such that one atom receives both electrons from a pair, and the other receives none. One positive and one negative atom are formed.
What are the differences in…
- speed of reaction
- reaction conditions
… between alkanes + halogens and alkenes + halogens?
- Speed of reaction is greatly reduced for alkanes (this is why organic compound + bromine water is still a good qualitative test for alkenes)
- Alkanes + halogens requires the presence of sufficient UV light
Why is UV light required during the reaction between an alkane and a halogen?
The UV light provides the initial energy required to enable homolytic fission to take place.
What three types of organic reaction mechanism do we need to be familiar with?
- Addition
- Substitution
- Elimination
What occurs during the initiation stage of the halogenation of an alkene?
The covalent bond within the halogen molecule undergoes homolytic fission in the presence of UV to form 2 halogen radicals.
What occurs during the propagation stage of the halogenation of an alkene?
The reaction propagates through a two-step chain reaction.
1. A halogen radical reacts with a C-H bond in methane to form a methyl radical and HBr.
2. This methyl radical reacts with a halogen molecule to form the halogenated product and a halogen radical.
What occurs during the termination stage of the halogenation of an alkene?
Two radicals collide, forming a stable molecule with all electrons paired. Any combination of radicals could react so there are a number of possible termination steps.
Name 2 limitations of radical substitution in organic synthesis.
- Further substitution - this can occur until all hydrogen atoms in a given organic compound have been substituted.
- Substitution can occur anywhere along the chain, giving rise to the formation of unwanted isomers.
What two types of bond make up a double bond, such as a C=C bond?
Sigma bond, and a pi bond.
How is a pi-bond formed?
- 3 electrons are involved in sigma bonds (orbital overlap)
- This leaves 1 unpaired electron per atom, occupying a p-orbital
- The two p-orbitals in a double bond (2 atoms) overlap above and below the plane of the bond
- This forms a pi bond
Why are pi bonds weaker than sigma bonds?
The electron density is spread above and below the nuclei, so electrostatic attraction between the nuclei and cloud of electron density falls. This gives pi bonds lower bond enthalpy.
Why do double bonds NOT have double the bond enthalpy?
Double bonds are made up of a pi bond and a sigma bond. These have varying bond enthalpies.
Why are alkenes more reactive than alkanes?
The pi-bond, which is only present in an alkene, breaks more readily as it has lower enthalpy. This occurs because the clouds of electron density in alkenes are attractive to electrophiles (electron pair acceptors).
What do curly arrows represent when we draw reaction mechanisms?
Movement of a pair of electrons.
Describe the process of electrophilic addition of hydrogen halides.
The pi bond breaks heterolytically, and its pair of electrons move down to bond with the electropositive hydrogen atom - an electrophile. The hydrogen halide’s bond then breaks heterolytically and electrons move to the halide, which then bonds with the carbocation.
Why do two products form when an asymmetrical alkene undergoes electrophilic addition?
Pi bonds can open up in two ways, so a major and a minor product is formed.
Why do non-equal amounts of major and minor products form during electrophilic addition?
The different carbocation intermediates that form when the pi-bond is broken have different relative stabilities. A more stable product produces more of its given product.
How do we determine relative stability of a carbocation?
The more the number of alkyl groups attacked to the carbocation, the more stable. We assign these as primary, secondary or tertiary.
What is the name of the law that enables us to determine the relative stabilities of carbocation intermediates?
Markownikoff’s rule.
How does the electrophilic addition of halogen molecules differ to that of hydrogen halides?
Normally a halogen molecule has no overall dipole as the electronegativity of both atoms is the same as- however, due to the high electron density of the C=C bond, like charges repel and an induced dipole forms. This allows electrophilic behaviour.
What major electrophilic addition processes can an alkene undergo?
- Addition of a hydrogen halide
- Addition of a halogen molecule
- Addition of H2O (to form an alcohol)
- Addition of H2 (hydrogenation to form an alkane)
What conditions are required for the electrophilic addition of H2O?
Presence of steam, (phosphoric) acid catalyst, high temperature
What conditions are required for hydrogenation?
Nickel catalyst, high temperatures, excess of hydrogen
Define stereoisomer.
A molecule with the same structural formula as the original but a different arrangement of atoms in space
Why does stereoisomerism occur around double bonds?
The pi-bond provides a cloud of electron density above and below the plane of the sigma bond. This restricts the rotation of groups.
What criteria are required for E/Z isomerism?
C=C double bond, different groups attached to each carbon
What is E/Z isomerism?
A certain case of stereoisomerism which only occurs in molecules with a C=C double bond.
How do we name molecules using E/Z convention?
- If groups of higher priority are diagonally arranged, it is an E-isomer
- If they are on the same side of the bond, it is a Z-isomer
What gives a subsequent group higher priority?
A greater number of electrons on the first atom - otherwise we look for the point of first difference.
What is cis-trans isomerism?
A special case of E/Z isomerism in which one of the attached groups must be the same on each carbon.
How do we designate isomers as cis- or trans-?
- Cis- isomers have the identical group on the same side of the C=C
- Trans- isomers have the identical group diagonally arranged across the C=C
How do we name addition polymers?
We name them after the monomers used to make them, with the prefix poly.
Why are polymers so useful in many applications?
They are…
- cheap
- abundant
- unreactive so do not readily degrade
Why are polymers generally unreactive?
They have only C-C single bonds (no pi-bond with reduced bond enthalpy), and overall no dipole due to little electronegativity difference in C-C, C-H bonds.
How are polymers conventionally recycled?
They are sort into types, chopped into flakes, washed, dried and melted, before forming pellets to make up new products.
Why is recycling PVC dangerous?
Burning it releases toxic hydrogen chloride gas, due to the polymer’s high chlorine content.
How do we recycle PVC nowadays?
We dissolve it in a solvent then recover it via precipitation.
Why are we able to easily use polymers as fuels? How can we use this to generate energy?
They have a very high stored energy value. The heat that is produced can be used to generate steam and operate a wind turbine.
What is feedback recycling and what are the benefits?
- It is used to reclaim monomers, gases and oils from waste polymers
- It produces similar products to that of a refinery
- The process can handle unsorted and unwashed polymers so it is safer
What are bioplastics?
Polymers formed from starch, cellulose, plant oils etc. as an alternative to the use of crude oil.
How do biodegradable polymers work?
They are broken down by organisms into molecules like water, CO2 and other common biological compounds.
Why are compostable polymers very useful?
They degrade to leave no toxic or visible residue, so are useful for composting waste in bags.
How do photodegradable polymers work?
They contain bonds which are weakened when they absorb UV light, or contain light absorbing additives. These help to initiate the process of degradation.
