Organic Chemistry I Flashcards
what is a hydrocarbon?
compound of hydrogen and carbon only
what is meant by homologous series?
organic compounds with same functional group + general formula
what is meant by functional group?
group of atoms in a molecule responsible for the characteristic reactions of that compound
what is addition?
joining of two or more molecules to make a larger molecule
what is substitution?
one species getting replaced by another
what is hydrolysis?
splitting a molecule into 2 new molecules by adding H+ and OH- derived from water
what is oxidation?
any reaction where a species loses electrons
what is reduction?
any reaction where a species gains electrons
what is the general formula for alkenes?
CnH₂n
what is the general formula for alkanes?
CnH₂n+2
are alkanes and cycloalkanes saturated or unsaturated?
saturated because they have single carbon bonds
what is the general formula for cycloalkanes?
CnH₂n
are alkenes and cycloalkenes saturated or unsaturated?
unsaturated because the double bond which allows them to make bonds with extra atoms in addition reactions
what test is used to identify the presence of a C=C bond?
-shake alkene with brown bromine water
and it should quickly decolourise
-this is because bromine is added across the double bond to form colourless dibromoalkane
halogen + alkene?
dihalogenoalkane
what is an electrophile?
electron-pair acceptors (electron poor so attracted to electron rich areas)
what is a nucleophile
electron-pair donors (electron rich so attracted to electron poor areas)
what is a radical?
-species with an unpaired electron (in mechanisms represented with a single dot)
-result of homolytic fission of a covalent bond
what is an isomer?
molecules with the same molecular formula but are arranged differently
what are the types of structural isomerism?
chain, positional, functional group
what is a chain isomer?
carbon skeleton can be arranged differently e.g. straight or branched
what properties are similar or different in chain isomers?
physical properties are different (e.g. boiling point) ,, branched chains do not pack closely together so intermolecular forces are weaker– lower bp
chemical properties are similar
what is a positional isomer?
functional group is attached to a different carbon atom
what properties are similar or different in positional isomers?
both chemical and physical properties are different
what is a functional group isomer?
when the same atoms are arranged into different functional groups
what properties are similar or different in functional group isomers?
both have very different physical and chemical properties
can atoms rotate around c-c bonds?
yes,, don’t be fooled something that looks like an isomer may not actually be one if the function group is attached to the same carbon in a different position
what is stereoisomerism?
have the same structural formula but a different arrangement in space,, only in double bonds
can double bonds rotate c=c?
no, because of the overlap of the p orbitals in an alkene to form a pi bond
what is cis isomerism?
Z,, on the same side (double bond only)
what is trans isomerism?
E,, opposite side (double bond only)
why do alkenes have stereoisomerism?
because of the lack of rotation within the double bond
what is a Z isomer?
same group on same side
what is an E isomer?
same group on opposite side
what do you need to do when naming stereoisomers?
put E/Z/cis/trans
what happens if all the groups are different in stereoisomerism?
atoms with a larger atomic number are given priority
what is homolytic fission?
-bond breaks evenly and each bonding atom receives one electron which is unpaired forming radicals
why are radicals highly reactive?
because of the unpaired electron
what is heterolytic fission?
-bond breaks unevenly so one of the bonding atoms receives both electrons from the bonded pair
-two different substances are formed e.g. cation or anion
what is a primary alcohol?
has one R-group
what is a secondary alcohol?
has two R-groups
what is a tertiary alcohol?
has three R-groups
what is a primary halogenoalkane?
one alkyl group
what is a secondary halogenoalkane?
two alkyl groups
what is a tertiary halogenoalkane?
three alkyl groups
what is a halogenoalkane?
alkanes with at least one halogen atom
when can halogenoalkanes be classified into primary, secondary and tertiary?
if they have just one halogen atom
how do alkenes form polymers?
through addition polymerisation
how can chemists limit the problems caused by polymer disposal?
-developing biodegradable polymers
-removing toxic waste gases caused by incineration of plastics
what conditions do photochemical reactions require?
UV (light)
how do halogens react with alkenes to from halogenoalkanes?
photochemical reactions using UV light then radical substitution
what are the three stages of radical substitution?
initiation, propagation, termination
what happens during the initiation step of radical substitution?
-radicals are produced (photodissociation)
-diatomic halogen bond splits equally and each atom keeps one electron (homolytic fission)
-atom becomes highly reactive radical due to unpaired electron
what happens during the propagation step of radical substitution?
-radicals are used up and created in a chain reaction
-radical attacks alkane forming alkane radical
-alkane radical attacks second halogen molecule
-new halogen radical can attack another alkane molecule until all the non radicals are wiped out
what happens during the termination step of radical substitution?
-two free radicals join together to form a stable molecule
-there are many possible termination reactions
what bonds does an alkene have?
both sigma and pi bonds (like hot dog) sigma bond sandwiched between pi bond
which has a higher electron density pi or sigma and how is it formed?
sigma bonds,, two orbitals overlap in a straight line in the space between two atoms giving highest possible electron density=strong electrostatic attraction=highest bond enthalpy
how is a pi bond formed?
two lobes of two orbitals overlap sideways making the electron density more spread out as it is above and below the nuclei=weaker electrostatic attraction
what does adding hydrogen to a C=C bond produce?
an alkane- ethene will react with hydrogen gas to produce ethane but only in the presence of a nickel catalyst at a temp of 150 C
why do electrophilic addition reactions happen to alkenes?
the double bond has lots of electrons so attracts electrophiles which are electron pair accepting e.g. positive ions like H+
what is a carbocation?
organic ion containing positively charged carbon atom
how is margarine formed from vegetable oil?
by the catalytic hydrogenation of unsaturated vegetable oil double bonds are removed ∴ raising the melting point of the oil so it is solid at room temperature
how are halogenoalkanes formed from alkenes?
alkenes undergo electrophilic addition with hydrogen halides
how are dihalogenoalkanes formed from alkenes?
-halogen reacts with alkenes by electrophilic addition
-halogens add across the double bond and each of the carbon atoms ends up bonded to a halogen
how are alcohols formed by alkenes?
alkenes are hydrated by steam at 300 C and pressure of 60-70 atm with an acid catalyst
how are alkenes made with acidified potassium magnate
?
shake alkene with acidified potassium dichromate and the purple solution is decolourised then the alkene has been oxidised and a diol (alcohol with two -OH) is made
what are the products of incomplete combustion?
C, CO2, H2O
what are the products of complete combustion?
CO2, H2O
what is crude oil made from?
alkanes
how can crude oil be made useful?
by fractional distillation- it turns crude oil into useful fractions
how can different alkanes in crude oil can be separated by fractional distillation?
different alkanes have different boiling points due to the different carbon chain lengths
how are alkane molecules attracted to each other?
by intermolecular forces
are alkanes polar or non-polar?
non-polar because carbon and hydrogen have similar electronegativites
are alkanes soluble in water?
no, alkanes have no permanent dipoles so cannot form hydrogen bonds
why are alkanes generally unreactive?
because of the strong covalent bonds between hydrogen and carbon
what happens when alkanes are combusted (burned with enough oxygen)?
products are CO2 and water (gas forms)
what happens when alkanes are combusted (burned with little oxygen)?
incomplete combustion- carbon monoxide, water, carbon are products (may still be some CO2)
how do catalytic converters solve the problems caused by pollutants?
-stop engines releasing pollutants such as carbon monoxide, oxides of nitrogen and unburnt hydrocarbons using a platinum catalyst to change the harmful pollutants to harmless gases e.g. water vapour and nitrogen and less harmful ones like CO2
