Module 4 (chapter 11, 12 and 13) - organic chemistry Flashcards
Hydrocarbon
A compound made of only hydrogen and carbon atoms
Saturated
Compounds with single carbon-carbon bonds only
Unsaturated
Compounds with the presence of multiple carbon-carbon bonds including double, triple and aromatic rings
Aromatic
A compound containing a benzene ring
Aliphatic
A compound containing carbon and hydrogen joined in straight chains, branched chains or non-aromatic rings
Alicyclic
An aliphatic compound arranged in non-aromatic rings with or without side chains
Homologous series
A series of organic compounds having the same functional group but with each successive member differing by CH2
Functional group
A group of atoms responsible for the characteristic reactions of a compound
Molecular formula
The number and type of atom of each element in a molecule
Empirical formula
The simplest whole number ratio of atoms of each element present in a compound
Structural formula
The minimal detail that shows the arrangement of atoms in a molecule
E.g. butane = CH3(CH2)2CH3
Displayed formula
The relative position of atoms in a molecule and the bonds between them
Skeletal formula
The simplified organic formula shown by removing hydrogen atoms from carbon chains leaving the carbon chain and functional group
General formula
The simplest algebraic formula of a member of a homologous series
Alkene
C=C (ene)
Alcohol
OH (ol)
Aldehyde
CHO
Double bonded O and single bonded H on the end of the group
(Al)
Ketone
C=O
(In the middle of a group)
(-one)
Carboxylic Acid
COOH
C double bonded to O and then single bonded to O and H
(-oic Acid)
Amine
NH2
C bonded to N and then N bonded to two hydrogens
(Amine)
Chloro/bromo/iodo alkane
Cl, Br, I
- replaces a hydrogen
- chloro, bromo, iodo before alkane
Structural isomer
Compounds with the same molecular formula but a different structural formula (e.g. but-1-ene and but-2-ene)
Benzene ring and how is it drawn?
Six carbons all joined in a cyclical structure
-extra electrons form delocalised rings around it as each carbon should form 4 bonds but only 3 are shown. This is shown by a centralised circle in the compound
Alkyl
A stem meaning not all atoms are connected in a single chain
How do you write the alkyl stems?
The number of carbons determines its name
E.g. 1 carbon is called methyl
-you write them in alphabetical order when ordering the alkyl stems
what happens to the trend in boiling points of hydrocarbons?
as hydrocarbon chains get longer there boiling point increases
- this is because there are more points of contact and hence more longer dispersion forces
- therefore more energy is required to overcome these forces increasing the boiling point
why do alkanes have low reactivity?
- due to their high bond enthalpy
- the very low polarity of the sigma bond as the electronegativity of carbon and hydrogen is thought to be so similar the bond is considered non-polar
what is a sigma bond?
the overlap of the orbitals directly between the bonding atoms
- each overlapping orbital contains one electron so the sigma bond has two electrons shared between the bonding atoms
- the sigma bond acts as an axes around which the atoms can rotate freely so these shapes can rotate an aren’t rigid
what is the effect of branching on boiling point?
- increased branching decreases boiling point as there are fewer points of contact so fewer London dispersion forces hence less energy is needed to overcome them
- branching also weakens molecules ability to tesselate reducing their attraction and intermolecular forces further
what is the shape of alkanes?
-each carbon atom is surrounded by four electron pairs in four sigma bonds forming tetrahedral structure
why are alkanes used for combustion?
- all of them react with a plentiful supply of oxygen to produce carbon dioxide and water
- don’t produce toxic products
- easy to transport
- readily available
general equation for balancing combustion of alkanes
CxHy + (x + y/4)O2 —- xCO2 + y/2 H2O
what is incomplete combustion?
- happens when there is a limited supply of oxygen
- this results in the hydrogen atoms in the alkane always being oxidised into water but combustion of the carbon may be incomplete
- this forms carbon monoxide, water, and carbon particulates
what is bad about carbon monoxide?
- colourless odourless tasteless gas which is highly toxic
- it combines irreversibly with haemoglobin in the blood forming carbooxyhaemoglobin preventing oxygen being transported around the body
- can lead to poisoning and death
what are stereoisomers?
compounds with the same structural and molecular formula but different arrangements of atoms in space
- this is due to a lack of rotation around the double bond
how do you name E and Z isomers?
if the two highest priority groups are on the same side of the C=C double bond it is a Z isomer, if they are on different sides its an E isomer
-compounds have priority if they’re heavier (larger mass number)
how do you name using Cis-trans notation?
- this is a form of E/Z notation yet in this case one of the groups attached to each carbon atom must be the same
- cis isomer is the Z isomer
- trans isomer is the E isomer
what are the CIP rules?
-in the system, the atoms attached to each carbon atom in a double bond are given priority based off their mass number
what is the structure of alkenes?
- unsaturated hydrocarbons
- they contain at least one double carbon bond
- general formula c2h2n
- cyclic alkenes or alkenes with more than one double bond don’t obey this formula
what is the nature of the alkene’s double bond?
- four electrons on carbons outer shell
- for each carbon atom of the double bond, three of the four electrons are used in sigma bonds and one is used in a pi bond (in a p orbital, one from each carbon atom of the double bond)
- the pi electron density is concentrated above and below the nuclei of the bonding atoms
what is the effect of the pi bond on the double bond?
it locks the two carbon atoms in place preventing rational movement around the bond
-this makes their geometry different to that of alkane
what is the shape of alkenes?
- they form a trigonal planar shape
- there are three regions of electron density around each of the carbon atoms
- three regions repel each other ad far apart as possible forming 120 degree bond angles
- all of the atoms are in the same place
what must a molecule have to satisfy E/s isomerism?
- a C=C double bond
- different groups attached to each carbon atom of the double bond
what are the bond enthalpies of carbon bonds?
c-c is 347kjmol-1 (sigma bond)
c=c is 612kjmol-1 (sigma bond and pi bond)
therefore bond enthalpy of pi bind is 265kjmol-1
it is weaker than the sigma bond so is broken more easily
what is an addition reaction?
the addition of a small molecule across the double bond causing the pi bond to break and form new bonds
what happens in the hydrogenation and halogenation of alkenes?
- when reacted with hydrogen and passed over a nickel catalyst at 423K or reacted with halogens at room temperature an addition reaction happens
- hydrogen or the halogen is added across the double bond
- the more double bonds the more of this molecule needed to react
how do you test for unsaturation?
- add bromine water dropwise to a sample of an alkene
- if carbon bond is present a bromine addition reaction happens across the double bond so sample turns from orange to colourless
- if compound is saturated then no addition reaction happens so the solution isn’t decolourised
what happens in the addition reactions of alkenes with hydrogen halides?
- at room temperature they react to form haloalkenes
- there are two possible products
what happens in the hydration of alkenes?
- alcohols are formed when alkenes react with steam in the presence of a prosperous acid catalyst
- steam is added across the double bond
- there are two possible products
what does the double bond in an alkene represent?
- a region of high electron density due to the presence of the pi bond
- this attracts electrophiles
what is an electrophile?
- an atom or group of atoms that is attracted to an electron rich centre and accepts an electron pair
- it is usually a positive ion or a molecule containing an atom with a partial positive charge
what are the mechanism steps for the electrophilic substitution reactions of alkenes?
- the halogen atom in a hydrogen halide is more electronegative than hydrogen so it is polar (H is delta positive and halogen delta negative)
- the electron pair in the pi bond is attracted to the electronegative halogen atom
- a bond forms between the hydrogen atom of the H-Br molecule for example, and a carbon atom that was part of the double bond as the delta positive hydrogen is attracted to the electron rich double bond
- the H-Br bond breaks by heterolytic fission with the electron pair going to the halogen atom
- a bromide ion and a carbocation are formed
- the halogen ion reacts with the carbocation to form the addition product
how is a dipole induced in electrophilic reactions of alkenes with diatomic halogen molecules?
- when bromine approaches an alkene the pi-bond interacts with the electrons in the Br-Br bond
- this interaction causes polarisation of the bond with one end becoming delta positive and the other delta negative (induced dipole)
- this happens because electrons repel each other so the pair of electrons in the Br-Br bond sit closer to the further atom
after inducing a dipole, what is the mechanism for the electrophilic reactions of alkenes with diatomic halogen molecules?
- the electron pairs in the pi bond is attracted to the delta positive end of the bromine bond causing the double bond to break
- a covalent bond now forms between one of the carbon atoms and a bromine one
- the Br-Br bond breaks by heterolytic fission with the electron pair going to the delta negative side of the Br bond
- a bromine ion and carbocation form
- the bromine ion reacts with the carbocation to form the addition product of the reaction
what is a carbocation?
an organic ion in which a carbon atom has a positive charge
what is Markovnikov’s rule?
when a hydrogen halide reacts with an unsymmetrical alkene the hydrogen becomes attached to the carbon with the most hydrogens attached to it already
what are primary and secondary carbocations?
- the primary carbocation is when the positive charge is on a carbon atom at the end of a chain
- secondary carbocation is when the positive charge is on a carbon atom with two carbon chains attached
which carbocations are the most stable?
tertiary carbocations are the most stale
primary carbocations are the least stable
why are certain carbocations more stable?
- the more methyl groups the greater the inductive effect
- therefore the carbon atom with the most carbon chains has greatest inductive effect so is most stable and therefore is mist likely to form
why are more alkyl groups more stable?
- each alkyl group donates and pushes electrons towards the positive charge of the carbocation
- the positive charge is spread over the alkyl groups so the more ally groups the more spread out charge is
- this makes it more stable
what yield of products are created in these addition reactions?
- the intermediate carbocation formed is secondary
- this means it is more stable as it has two inductive effects
- this makes it more likely to form increasing the yield of that product
what is the reaction of alkanes with halogens?
in the presence of sunlight alkanes react with halogens as the high energy UV radiation provides the initial energy for a reaction to take place
what is fission?
- the breaking of a covenant bond
- homolytic = “ “ with one of the bonded electrons going to each atom
- heterolytic = “ “ with both of the bonded electrons going to one of the atoms forming a cation and anion
what is stage one of the substitution for the radical substitution of alkanes
- initiation is when the covelant bond in a halogen molecule is broken homolytically
- this forms two highly reactive halogen radicals
what is stage two for the radical substitution of alkanes?
- propagation when radicals attack the alkane
- propagation tends to terminate when two radicals collide
- first step = one of the halogen radicals steals one of the hydrogen atoms forming a carbon radical and a hydrogen halide
- step 2= the carbon radical reacts with another halogen molecule to form a haloalkane and to regenerate a halogen radical
what is stage three for the radical substitution of alkanes?
- termination
- two radicals collide and combine forming a molecule with all electron pairs
- when two radicals react both are removed from the reaction mixture stopping the reaction
what are the limitations of radical substitutions in organic synthesis?
- further substitution happens and can continue until all hydrogen atoms have been substituted
- this results in a mixture of products
- it also creates substitution at different positions in carbon chains creating mixtures of mono substituted isomers
what is a mechanism?
a sequence of steps showing the path taken by electrons in a reaction
what is a monomer and polymer?
monomer= the small molecules which join together to make a polymer
polymer=long chain molecule that is made from the same repeating unit
what is addition polymerisation?
process by which many unsaturated alkene molecules add on to a growing polymer chain at one time to form a very long saturated molecular chain
-they have high molecular mass
how do you write polymers?
- put repeating unit in square brackets with bonds coming outside of them
- after the bracket place a letter n to represent large number of repeating units
- naming them by putting monomer name in brackets with poly before it
uses of poly(propene)
- childrens’ toys
- packing crates
- guttering and window frames
uses of poly(styrene)
- packing material
- food trays and cups due to thermal insulating property
uses of PTFE
- used as coating for non stick frying pans
- permeable membrane for clothes and shoes
- cable insulation
what is good and bad about recycling polymers?
- conserves finite reserves like fossil fuels and decreases the amount sent to landfill
- yet can only be recycled a finite number of times and when miseducating their properties are often rendered sometimes making it unusable
- long process to sort them out, they’re washed dried and melted before being made into pellets that can be reused
what is significant about recycling PVC?
- its disposal is hazardous dent high chlorine content and range of additives so landfill isn’t sustainable
- when burnt it also releases hydrogen chloride a corrosive gas and other pollutants like toxic dioxins
- therefore recycling it involves using solvents to dissolve the polymer which is then recovered by precipitation from the solvent which can be used again
what is good and bad about burning polymers for fuel?
- some polymers hold a high stored energy value
- they can be burnt to generate heat generating steam to turn a turbine and produce electricity
- this reduced reliance on things like fossil fuels
- yet produces harmful toxins through burning contributing to greenhouse effect
- also energy needed to burn it may be expensive
what is feedstock recycling?
describes the chemical and thermal processes that can reclaim monomers from waste polymers
-major bonus is that it is able to handle unsorted and unwashed polymers so is a quick snd simple process
what are bioplastics?
plastics produced from a biological origin like starch
what is good and bad about biodegradable polymers?
- broken down by micro-organisms into water, carbon dioxide and biological compounds
- they usually contain additives to alter the traditional structure of the polymer making them easier to break down
- compostable polymers leave no visible toxic residues
- they tend to be used in packaging, electronics and more fuel efficient transport vehicles
what are photodegradable polymers?
- oil based polymers
- these contain bonds which are weakened by absorbing sunlight to start the degradation
- light absorbing additives are also used
what is a better alternative to burning plastics?
gasification
-process which melts plastics at very high temperatures in the near absence of oxygen
-this generates a synthetic gas used to fire turbines but with natural gas
pyrolysis
-plastics are shredded and melted at even lower temperatures and in the presence if even less oxygen breaking them into shorter chained hydrocarbons
-these can be refined and used as fuel for other chemical products
drawbacks of biodegradable plastics?
- don’t always readily decompose some need access to UV light
- growing corn for starch uses up land that could be used to grow food perhaps leading to competition and shortages
- oxydegradable plastics often just float on water as fragments as it is too cold to break them down
what is a pi bond
- formed by the sideways overlap of p orbitals
- forms the second and third bond between atoms
ethyne
triple bond
CnH2n-2
