topic 6 - organic Flashcards
what is a hydrocarbon
a compound consisting of hydrogen and carbon only
what does it mean if an hydrocarbon is saturated
contain single carbon-carbon bonds only
what does it mean if an hydrocarbon is unsaturated
contains a C=C double bond
what is a molecular formula
the formula which shows the actual number of each type of atom
what is an empirical formula
shows the simplest whole number ratio of atoms of each element in the compound
what is a generic formula
algebraic formula for a homologous series e.g. CnH2n
what is a structured formula
shows the minimal detail that shows the arrangement of atoms in a
molecule, eg for butane: CH3CH2CH2CH3 or CH3
(CH2
)2CH3
what is a displayed formulaa
show all the covalent bonds and atoms present in a molecule
what is the shape around the carbon atom in saturated hydrocarbon
tetrahedral and the bond angle is 109.5
what is the skeletal formula
shows the simplified organic formula, shown by removing hydrogen atoms from alkyl chains,
leaving just a carbon skeleton and associated functional groups.
what is a functional group
is an atom or group of atoms which when present in different molecules
causes them to have similar chemical properties
what is a homologous series
families of organic compounds with the same functional
group and same general formula. *They show a gradual change in physical properties (e.g. boiling point).
* Each member differs by CH2
from the last.
* same chemical properties.
what is the order of precedence
Carboxylic acids >aldehydes>ketones>alcohols>alkenes>halogenoalkanes
what does the order of precedence determine
determines which groups are
named with prefix or suffix forms. The highest precedence group takes the suffix (and the lowest number on the carbon
chain), with all others taking the prefix form. However, double and triple C-C bonds only take suffix form.
what does aliphatic mean
carbon atoms that are joined to eachother in unbranchd or branched or non-aromatic ring. examples include alkanes, alkenes, and alkynes.
what does alicyclic mean
an organic compound that is both aliphatic and cyclic. they contain one or more all-carbon rings which may be either saturated or unsaturated but do not have aromatic character
what does aromatic mean
contains a benzene ring. aromatic compounds often have a distinct smell and are chemically stable due to this electron delocalization.
what is structural isomers
same molecular formula different structures (or structural formulae)
what is a chain isomer
Compounds with the same molecular formula but different
structures of the carbon skeleton
what is a position isomer
Compounds with the same molecular formula but different structures
due to different positions of the same functional group on the same carbon skeleton
what is a functional group isomer
Compounds with the same molecular formula but
with atoms arranged to give different functional groups
alkenes properties
- undergoes addition reactions
- non polar
- water insoluble
- reactive
- melting+boiling points increase with Mr
- C–C is non rotational
what is the mechanism for alkene to halogenalkane
electrophilic addition
what are the conditions needed for hydrogenation ( addition reaction )
- nickel or platinum catalyst
- 150 degrees
- add H2
what are the conditions needed for hydration
- add H2O
- concentrated phosphoric acid catalyst
- steam ( >100 ) - high temp
- high pressure 70 atm
product of hydration of an alkene
alcohol
product of hydrogenation of alkene
alkane
type of bond fission in electrophilic addition
heterolytic
conditions for electrophilic addition
room temperature
what is important about addition polymerisation reaction
100% atom economy
monomer to polymer / alkenes to longer saturated chains
addition polymerisation
key facts about polymers
- unreactive because saturated
- intermolecular forces vary depending on their side groups
- non polar = london forces
- polar = dipole / hydrogen bonding
what are the methods of disposal of waste polymers
- recycling
- incineration
- feedstock for cracking
- bodegradable plastics
recycling
- some plastics can be remolded into new products ( thermosoftening)
- some products must be ‘chipped’ and reformed into new products
incineration of plastics
- plastics can be burned for energy production
- halogen containing plastics (e.g, PVC)
- these must be removed during the process (e.g, by neutraliztaion)
feedstock
- may be ‘cracked’ to produce smaller, more useful alkenes+alkanes
- could be used for fuels for production of other organic chemicals
degradable plastics
- biodegradable: broken down by plastics
- photodegradable: broken down by UV light
general formula for halogenoalkanes
CnH2n+1X
properties of halogenoalkanes
- saturated
- polar
- halogen is highly electronegative
- not water soluble ( not polar enough to react with water )
- varied melting and boiling points : permanent dipoles / higher melting and boiling points than corresponding alkane ( alkanes have an induced dipole )
2 main reactions of halogenoalkanes
- nucleophilic substitution
- elimination reaction
what is the purpose of nucleophilic substitution
- release halide ion which can be tested for since you are unable to test for halogenoalkanes when the halogen is bonded to carbon
test for halogenalkanes
1- reflux it with aqueous sodium hydroxide ( nucleophilic reaction ). mix both with ethanol
2- add excess nitric acid
3 - add silver nitrate and observe colour change
why do we need to add excess nitric acid
to neutralize excess OH- ions because the next step is to add silver nitrate to test for halide ions.
if OH- ions present then Ag+ will react with OH- to produce AgOH ( solid brown precipitate )
which will interfere with the test
why not use hydrochloric acid or sulfuric acid instead of nitric acid ( test for halides )
would react with Ag+ to form white precipitates which would interfere with the test
what is the follow up test for halide ions
- concentrated ammonia or dilute ammonia
- silver chloride redissolves in dilute and concentrated
- silver bromide will only redissolve in concentrated ammonia
- silver iodide will not redissolve in either
what does the ease of substitution depend on
bond enthalpy of carbon-halogen
what happens in an elimination reaction
removes a small molecule (often water) from the organic molecules
how to distinguish if it is a substitution or elimination reaction
aqueous : substitution
alcoholic : elimination
properties of alcohols
- CnH2n+1OH
- saturated
- polar dipole across O-H bond
- tetrahedral / OH is bent because of the 2 lone pairs
- water soluble (OH dipole allows molecule to interact with H2O via hydrogen bonding )
- varied Tm and Tb : hydrogen bonding IMF’s due to OH, higher than corresponding alkane, alkene and halogenoalkane
what are the reactions that alcohols undergo
- oxidation
- dehydration ( elimination )
- substitution
what is the trend in solubility for alcohols and why
- decreases with increased chain length
- because as non - polar section gets bigger, the O-H gets less significant
trend for melting and boiling point of alcohols
as the chain length increases, melting and boiling points increase due to stronger induced dipoles
how do we produce alcohols
- nucleophilic substitution of halogenoalkanes
- hydration of alkenes
- fermentation
observations when sodium reacts with alcohols
- effervescence
- mixture gets hot
- sodium dissolves
- a white solid is produced
oxidation of primary alcohols
partial oxidation : alcohol to aldehyde + H2O
full oxidation : alcohol to ccarboxylic acid + H2O
oxidation of secondary alcohols
secondary alcohol to ketone
what is the oxidising agents used in oxidation of alcohols
- acidified potasium manganate 7 OR H+/MnO4- ( +7 to +2 gets reduced itself ) goes from purple to colourless
- potassium dichromate 6 solution and dilute sulfuric acid OR H+/ CR2O7^2- ( +6 to +3 reduced itself ) goes from orange to green
conditions of partial oxidation of primary alcohols
use a limited amount of dichromate warm gently and distil out the aldehyde as it forms
conditions of full oxidation of primary alcohols
use and excess of dichromate and heat under reflux, distill off product after the reaction has finished
conditions of oxidation of secondary alcohols
heat under reflux
oxidation of tertiary alcohols
cannot be oxidised at all by potassium dichromate because there is no hydrogen atom bonded to the carbon with the OH group
testing for aldehydes vs ketones
- aldehydes can be further oxidised to carboxylic acid but ketones cannot
- tollins reagant ( NH3 + AgNO3/ ammonical silver nitrate ) OR fehlings solution containing blue Cu2+ ions
- heat gently
- positive result : silver deposit = aldehyde
- negative result : no visible reaction = ketone
positive result ( fehlings solution ) = red precipitate of Cu2O = aldehyde
test for carboxylic acids
- add sodium carbonate solution
- positive result : effervescence caused by release of CO2 during neutralization
how to produce hlogenoalkane from alcohol
- nucleophilic substitution
how to form chloroalkane from alcohol
- phosphorus chloride ( PCl5 )
R-Cl + PCl5 –> HCL (g) + POCl3 + R-Cl - room temp
how to form bromoalkane from alcohol
- hydrogen bromide
HBr is produced in situ
( react alcohol with conc sulfic acid and potasium bromide to produce HBr )
—> R - Br + H2O - needs to be refluxed
- seperate bromoalkane by distillation
how to form iodoalkane from alcohol
3 R - OH + PI3 –> 3 R-I + H3PO3
PI3 produced in situ
( react alcohol with red phosphorus (2P) + 3I2 ( iodine )
- reflux then distill
how to form alkene from alcohol
- dehydration ( elimination reaction )
- concentrated phosphoric acid or sulfuric acid catalyst
- heat over solid aluminium oxide
- warm under reflux
