topic 6 - organic chemistry Flashcards
what are isomers
molecules with the same molecular formula but different arrangement of atoms (structural formula)
what are the 3 types of structural isomerism
chain
position
functional group
what is chain isomerism
-the carbon chain is branched in a different way
-e.g. a straight chain and a branched chain, but both have the same molecular formula
-butane and 2-methylpropane : C4H10
what is position isomerism
-the functional group is in a different position
-e.g. pent-1-ene and pent-2-ene : C5H10
what is functional group isomerism
-the position or arrangement of the atoms means that the functional group is changed completely
-e.g. alcohols and esthers
what are the 3 main parts to naming an organic compound
stem - number of carbon atoms in the longest chain containing the functional group
e.g. eth, meth, prop
prefix - showing the position and identity of any side chains
e.g. 1-methyl
suffix - an ending showing what functional group is present
what are the general steps to naming a molecule
-find the longest chain, assign a stem
-find the functional group, assign a suffix
-identify the name of any side chains
-number the principle chain so any side chain are given the lowest possible number
(side chain names appear in alphabetical order)
(if there are identical side chains, add di,tri or tetra to the prefix)
(numbers are separated from names by a hyphen)
(numbers are separated from numbers by a comma)
how do you name haloalkanes
-use the stem and suffix based on the original alkanne
-add a prefix indicating the halogens position and then the element
-bromo, chloro, iodo, fluoro
-e.g. 2-chloro-2-methylpropane
how do you name alcohols
-select the longest chain containing the OH functional group
-remove the e off the alkane name and add the suffix ol
-number the chain starting with the end nearer to the OH group
-the number is placed after the an but before the ol e.g. butan-2-ol
-add the correct prefix for any alkyl substituents e.g. 5-methylhexan-2-ol
define functional group
an atom or group of atoms that give the molecule or compound it’s distinctive and predictable properties
what is a homologous series
-a set of compounds with the same functional group
-differ by CH2
-have similar chemical and physical properties that show a gradual change
-have the same general formula
what is an organic compound
a compound that contains at least 1 carbon atom covalently bonded to at least 1 other element
what is a hydrocarbon
a molecule containing hydrogen and carbon atoms only
what are cycloalkanes
-saturated hydrocarbons
-the carbon chain forms a continuous ring
What is the name of the NH2 functional group
Amine group
What is a functional group
A group of atoms in a molecules which determines its reactivity and chemical properties
What are the 5 characteristics of a homologous series
-same functional group
-neighbouring molecules differ by CH2
-have similar chemical properties
-show a gradual change is physical properties
-same general formula
Why do molecules with longer carbon chains have stronger intermolecular forces
They have more electrons
Have stronger temporary dipoles
As the length of the carbon chain increases the melting point
Increases
As the length of the carbon chain increases the melting point
Increases
what are the 3 ways to convert crude oil into fuels
fractional distillation
cracking
refining
describe the process of fractional distillation
-crude oil is heated into a vapour
-there is a temperature gradient within the fractional column, it’s hotter at the bottom and cooler at the top
-the vapour passes up the column through a series of bubble caps
-different fractions condense at different heights depending on their boiling point
what are the lengths and boiling points of alkanes at the top and bottom of a fractional column
top: shorter length chains and lower boiling points
bottom: longer length chains and higher boiling points
why is cracking useful
-there is a higher demand for shorter chain alkanes than longer chain alkanes
-because they are better fuels
-so there is a surplus of long chain alkanes
describe the process of cracking
-the long chain alkanesare passed through a heated catalyst (e.g. zeolite)
-for each 1 long molecule, at least 2 smaller molecules are formed alkanes and alkenes
out of straight chain, branched and cyclic alkanes, which are the most efficient as fuels
-cycloalkanes are the most efficient because they burn more efficiently
-then branched
-then straight chains
describe the process of reforming
-hydrocarbons are heated with a catalyst (e.g. platinum)
-straight chain alkanes are converted into branched and cycloalkanes
-the products of the reaction are usually a cyclo/branched alkane + H2
what conditions must be present for the substitution reaction of alkanes halogenation
-at room temperature the mixture must be exposed to ultraviolet light
-or if the temperature is increased a reaction will eventually occur
what is a free radical
a species that contains a single unpaired electron
is formed by homolytic fission of a covalent bond
why is free radical substitution not an efficient reaction
-it is likely that further substitution reactions will occur beyond the desired product
-so the yield of the desired product will be low
-and the products will have to be separated
what mechanism and type of reaction do alkanes undergo
(mechanism)Free radical substitution
(type)homolytic fision
what is the general formula for alkenes
CnH2n
why type of bonds does a double bond contain
1 sigma bond
1 pi bond
what is a sigma bond
when 2 electron orbitals from 2 different atoms overlap end on forming a covalent bond
what is a pi bond
when electron orbital overlap sideways forming a covalent bond
describe what happens to the bonds in alkenes during addition reactions
-the double bond becomes a single bond
-the sigma bond remains unchanged
-the pi bond electrons are used to form new bonds with another molecule
-the reaction forms a product with sigma bonds, so it is saturated
-as the product has sigma bonds and no pi bonds, it is more stable
which are stronger, sigma bonds or pi bonds, why?
-sigma bonds
-because the electrons in the sigma bond is closer to the carbon atoms
-so is more strongly held by the carbon atoms
what is the test for a carbon double bond
what is the positive and negative result
alkene + bromine water
positive result: the bromine water is decolourised, it goes from orange-brown to colourless
negative result: remains an unchanged orange-brown colour
describe the test for a carbon double bond
-its an addition reaction between an alkene (e.g. ethene) and bromine water
-the pi bond in the double bond breaks, these electrons are now used to form a sigma bond between the carbon atom and bromine atom (twice)
-the sigma bond between the carbon atoms remain
E.g. C2H4 + Br2 = C2H4Br2
what is hydrogenation
are there any required conditions
-an addition reaction where hydrogen is added to an alkene
the product is 1 alkane
-a nickel catalyst and heat are required
describe one of the uses of hydrogenation
-manufacturing of margarine
-vegetable oils are unsaturated so contain a carbon to carbon double bond
-when vegetable oils undergo hydrogenation some of the double bonds become single bonds
-this changes the propterties of the vegetable oil, making it a solid
describe halogenation reactions
are there and required conditions
-addition reactions between an alkene and a halogen
-the products are 1 dihalogenoalkane
-no required conditions
describe hydration reactions
are there any required conditions
-addition reactions
-an alkene is heated with steam, then passed through a a catalyst of phosphoric acid (H3PO4)
-H and OH are added to the carbon atoms on the double bond
-the product is an alcohol
-the only required condition is heat
describe addition of hydrogen halides reactions
are there any required conditions
-addition reaction between an alkene and a hydrogen halide
-the product is 1 halogenoalkane
-there are no required conditions
describe oxidation to diols reactions
are there any required conditions
-oxidation followed by addition
-the required conditions are potassium manganate in acidic conditions (solution of dilute sulfuric acid)
-the potassium manganate provides 1 oxygen atom (oxidation)
-the acid solution provides 1 oxygen atom and 2 hydrogen atoms
-so there is an addition of 2 OH groups across the double bond
-the product is an alkanediol
what is an electrophile
a species that is attracted to negative charge
what is the mechanism of the reaction between ethene and hydrogen bromide
electrophilic addition
in an electrophilic addition reaction involving alkenes when can there be more than 1 possible product formed
when the alkene and attacking molecule are unsymmetrical
what does it mean when a carbocation is described as primary, secondary or tertiary
primary carbocation: the carbon atom with the positive charge is joined to 1 alkyl group
secondary carbocation: the carbon atom with the positive charge is joined to 2 alkyl groups
tertiary carbocation: the carbon atom with the positive charge is joined to 3 alkyl groups
tertiary carbocations are the most stable, then secondary, then primary
because alkyl groups are electron-releasing so when there are more of them the positive charge is spread more than when there is only one, when the positive charge can be spread over more atoms the carbocation is more stable
what are the major product and minor product formed from using Markovnikoff’s rule
Markovnikoff’s rule: the major product will be formed through the route of the more stable carbocation (only applies to unsymmetrical alkenes and attacking molecules)
the major product is formed from the more stable carbocation
the minor product is formed from the less stable carbocation
what are the products of homolytic fission
results in free radicals
what are the products of heterolytic fission
results in ions
Why do polymers have a higher melting point than their monomers
There are more electrons in the polymer
So stronger van der walls forces
So more energy needed to break bonds
what are 4 reasons for the increase use of polymers
-polymers can be manufactured on a large scale, with a variety of shaped and physical properties
-they can be lighter in weight than traditional alternatives (glass milk bottle vs plastic bottle)
-polymers are unreactive so can contain many substances for long periods of time
-polymers are relatively cheap to make
instead of putting polymers into landfill they can be put to other uses, what are 3 of these other uses
-recycling
-incineration
-use as a chemical feedstock
briefly describe the process of recycling
-sorting,because different types of polymers cannot be processed together
-processing, involves cutting the polymers into small pieces and washing them
-this material is used to make a new material through melting and moulding
describe incineration
-most polymers are made from carbon and hydrogen so can be used as fuels
-an incinerator takes in polymer waste and converts it into thermal energy which is used to heat homes or generate electricity
what is a disadvantage of incineration
-polymers can contain other elements apart from hydrogen and carbon, which when burnt and released into the air can cause air pollution
describe how polymer waste can be used as chemical feedstock
-polymer waste is broken down into gases
-this is used as a feedstock which can be used in other chemical reactions
what are biodegradable polymers
polymers that can be broken down by microbes in the environment
what are the 2 disadvantages of biodegradable polymers
-biodegradable polymers are often made from plants, land is needed to grow these plants, so there will be less land for livestock and food for humans
-when the polymer breaks down the carbon and hydrogen atoms within it cannot be recycled, incinerated or used as chemical feedstock
what makes halogenoalkanes reactive
the halogen is more electronegative than the carbon atom
so the halogen is delta negative and the carbon is delta positive
what is a nucleophile
a species that donates a lone pair of electrons to form a covalent bond with an electron-deficient atom
why do alcohols have a higher boiling point compared to alkanes with the same molecular mass
-alkanes just have london forces between molecules
-but alcohols have london forces and hydrogen bonding between molecules
-hydrogen bonds form between the delta positive hydrogen in the hydroxyl group of 1 molecule and the delta negative oxygen on another molecule
-so more energy is required to separate molecules in an alcohol
what is the functional group of an aldehyde
=0
-H
this OH group must be on the end of the carbon chain
what is the functional group of a ketone
=0
must be in the middle of the carbon chain (not on any of the 2 end carbons)
how do you name an aldehyde
-al
how do you name a ketone
-one
what is the functional group of a carboxylic acid
=O
-OH
can only be on the end of the carbon chain
how do you name a carboxylic acid
-oic acid
why is free radical substitution of alkanes not an efficient reaction
-further substitution reactions can occur, so the yield of the desired product will be low
-there will be a mixture of products that need to be separated, this requires more energy making the reaction more expensive
what are the only 2 products formed from the complete combustion of an alkane
carbon dioxide + water
what are the possible products of incomplete combustion of an alkane
water (always formed)
carbon (soot)
carbon monoxide
carbon dioxide
unburned hydrocarbons
explain why the pollutatnt carbon monxide is harmful
-it is fatal
-carbon monoxide binds to the hemoglobin in the blood, which prevents hemoglobind binding to oxygen, so no oxygen is delivered to cells
-it is colourless and odourless
explain how oxides of sulfur are formed from the combustion of hydrocarbons and why they are pollutants
-crude oil can contain sulfur atoms which are not removed during the fractional distillation, cracking or reforming processes
-during combustion of alkanes the sulfur atoms react with oxygen in the air to form sulfur dioxide
-and this sulfur dioxide can react with more oxygen in the air to form sulfur trioxide
-sulfur dioxide and trioxide are acidic
-they dissolve in water in clouds in the atmosphere
-when sulfur dioxide dissolves in water, sulfurous acid is formed
when sulfur trioxide dissolves in water sulfuric acid is formed
-both acids form acid rain, which falls into rivers making them acidic and harming aquatic life, acid rain can damage crops and forests
what are 3 pollutants of incomplete combustion
carbon monoxide
oxide of sulfur
oxides of nitrogen
explain how oxides of nitrogen are formed from the combustion of alkanes and why they are pollutants
-combustion of alkanes happens at very high temperatures
-these high temperatures cause nitrogen molecules in the air to react with oxygen molecules in the air
-which form many different oxides of nitrogen (mainly nitrogen monoxide and nitrogen dioxide)
-when these gases dissolve in water in the atmosphere they form nitric acid and nitrous acid
-which form acid rain, if it falls into rivers it can make the rivers acidic and harm aquatic life, acid rain can damage crops and forests
what is the function of a catalytic converter
to remove harmful pollutants that are produced by the combustion of fuels in cars
e.g. oxidation of carbon monoxide to form carbon dioxide
oxidation of unburned hydrocarbons to form water and carbon dioxide
nitrogen monoxide and carbon monoxide react together to form nitrogen and carbon dioxide
explain how catalytic converters work
a metal (e.g. platinum) is spread thinly over a honeycomb mesh to increase surface area of the reaction
what are biofuels
fuels obtained from living matter that has died recently
describe what is meant by carbon neutral, using the combustion of wood as an example
when the tree grows it absorbs carbon dioxide from the atmosphere, so the carbon atoms become a part of the trees structure
when the tree is cut down and its wood is burnt, carbon dioxide is released into the atmosphere during combustion
if the same amount of carbon atoms are released out into the atmosphere as the amount taken in from the atmosphere during the tree’s growth, the wood is carbon neutral
state 2 alternative fuels
biodiesel
bioalcohols
why are biofuels not carbon neutral
the plants have to be harvested, transported to a factory, processed, then the products have to be transported to a point of sale, which all require energy, which is usually involves the release of CO2
so more CO2 is being released into the atmosphere than is being taken in by the plants
when comparing which biofuel is the most efficient and effective what are the 4 factors that need to be taken into account
-land use, the amount of land being used and should the land be used for other purposes (growing food for people)
-yield, how much crop can be grown on a given piece of land, what percentage of carbon and hydrogen atoms from the plant end up in the fuel
-manufacture and transport, how much energy is used in harvesting, processing and transporting the crop
-carbon neutrality, how close to carbon neutral is the fuel
assess the effectiveness and efficiency of biodiesel and bioethanol
-land use, a lot of land needed, which takes up land needed to grow food for people
-yield, low but gradually increasing with new developments
-manufacture and transport, relatively high cost in growing, processing and transporting
-carbon neutrality, much closer to carbon neutral than fossil fuels
what are biodiesels made from
made from vegetable oils from plants
what are bioalcohols made from
made from plant matter fermented by bacteria
assess the effectiveness and efficiency of natural gas
-land use, no land needed as the gas comes from underground sources
-yield, very high
-manufacture and transport, exploration and drilling costs are high, processing costs low, transport costs low as transported by pipeline
-carbon neutrality, very far from carbon neutral
what are the products of hydrolysis of a halogenoalkane
alcohol + hydrogenhalide
what colour is a chloroalkane when aqueous silver nitrate in ethanol is added to an alkane
colourless
what colour is a bromoalkane when silver nitrate is added to an alkane
cream
what colour is a iodoalkane when silver nitrate is added to an alkane
yellow
out of 1-iodobutane, 1-bromoalkane and 1-chloroalkane which reacts the fastest in a hydrolysis reaction
1-iodobutane
1-bromoalkane
1-chloroalkane
because breaking bonds requires energy
the C-I bond enthalpy is lowest
so under the same conditions the C-I bond is more likely to break
nucleophile definition
a species that donates a lone pair of electrons to form a covalent bond with an electron deficient atom
(attracted to delta positive atoms)
formed through heterolytic fission
what are the products of complete combustion of an alcohol
carbon dioxide and water only
an alcohol and an alkane have the same molecular mass, which has the higher boiling point
the alcohol
describe a qualitative test for a hydroxyl group
-react the sample (alcohol) with PCl5
-at room temperature
-if an OH group is present you will see “steamy fumes”
-which is gaseous HCl
-the products will be a chloroalkane, POCl3, HCl
how can you differentiate between a primary, secondary and tertiary alcohol
conduct oxidation reactions
what are primary, secondary and tertiary alcohols oxidised into
primary: aldehyde - carboxylic acid
secondary: ketone - doesn’t oxidise further
tertiary: doesn’t oxidise at all
during the first oxidisation of a primary and secondary alcohol, what happens
-oxidation is seen as the loss of hydrogen atoms
-1 hydrogen atom is lost from the OH group and another hydrogen atom is lost from the carbon atom which the OH group is also attached to
what qualitative test can be used to see if the alcohol which has been oxidised is primary or secondary
-react with Fhelings or Benedicts reagent
-a primary alcohol will have undergone 2 oxidation reactions, first into an aldehyde, then into a carboxylic acid
-the presence of a carboxylic acid will turn the reagent from blue to a red precipitate
-a secondary alcohol will only undergo 1 oxidation reaction into a ketone
-a ketone doesn’t react with the reagent, so the solution will stay blue
what is the colour change when Fhelings or Benedicts reagent is added to a carboxylic acid
from blue to a red precipitate
what is the colour change when Fhelings or Benedicts reagent is added to a ketone
it will stay blue (no reaction)
for the reaction between a halogenoalkane and ammonia what are the conditions needed, and products formed
conditions: heat under reflux with excess ethanolic ammonia under pressure
products: amine + ammonium halide (ethylamine)
for the reaction between a halogenoalkane and potassium cyanide what are the conditions needed, and products formed
conditions: dissolve in ethanolic potassium cyanide
products: nitrile + potassium halide
for the reaction between a halogenoalkane and ethanolic alkali what are the products formed
products: alkene + metal halide + water
for the dehydration of alcohols what are the conditions needed and products formed
conditions: phosphoric acid catalyst, heat under reflux at 180
products: alkene + water
describe the reaction for the chlorination of alcohols
reagent: PCl5
conditions: room temperature
products: chloroalkane + HCl (gaseous) + POCl3
describe the reaction for the bromination of alcohols
reagent: KBr + 50% concentrated H2SO4
conditions: heat under reflux
products: (2 step reaction) bromoalkane + water
describe the reaction for the iodination of alcohols
reagent: I2 + damp red phosphorous
conditions: heat under reflux
products: (2 step reaction) iodoalkane + phosphorous acid (H3PO3)
for the oxidation of alcohols what is the reagent used
acidified potassium dichromate (VI)
when a primary alcohol and an oxidising agent are heated under reflux what are the products
carboxylic acid + water
in a chemical equation do you need to balance the oxidising agent
yes
what makes a halogenoalkane primary, secondary or tertiary
primary-the carbon attached to the halogen is attached to 1 other alkyl group
secondary-the carbon attached to the halogen is attached to 2 other alkyl groups
tertiary-the carbon attached to the halogen is attached to 3 other alkyl groups
State the method used to produce a ketone
Heat an alcohol under reflux
State the method used to produce a carboxylic acid
Heat an a primary alcohol under reflux then separate using distillation
State the method used to produce an aldehyde
Distillation using a primary alcohol under
State the method used to produce an aldehyde
Distillation using a primary alcohol
