5.1-5.11 Flashcards
what is a hydrocarbon
a compound containing only hydrogen and carbon
what’s an aliphatic compound
strait chained, branched or cyclic hydrocarbons that don’t contain aromatic groups
what is an aromatic compound
hydrocarbons containing a benzene ring
define ‘homologous series’
a series of organic compounds with the same functional group but successive members differ by CH2
what’s carbons electron configuration and how can it form 4 single bonds
1s2, 2s2, 2p2. one of the electrons in the electron pair in the 2s orbital can be promoted to the 2p orbital (hybridisation). this gives four unpaired electrons that can form covalent bonds
how can organic compounds be named
count the Carbons in the longest chain
name each attached alkyl group
number each carbon in the longest chain so that the first attached group has the smallest number
each alkyl group is named in alphabetical order
what are the chemical properties of cycloalkanes
unreactive (due to strong non polar bonds)
react with oxygen in combustion reactions
react with halogens in the presence of UV light
how does combustion analysis work
the empirical formula of a hydrocarbon can be found
the mass/volume of CO2 and H2O given off are measured
calculate the moles of CO2 and H2O. moles of C = moles of CO2. Moles of H = 2* moles of H2O.
find the smallest whole number ratio of these two values
why is carbon monoxide poisonous
it binds to haemoglobin preventing oxygen from being carried around the body. this causes oxygen deprivation which can be fatal
why does branching decrease the boiling point of hydrocarbons
this only applies if a branched hydrocarbon has the same molecular formula (e.g. C4H10). the branching causes molecules to be unable to pack together as tightly, reducing surface area of contact. this causes weaker induced dipole-dipole forces
trend in physical properties of hydrocarbons
longer chains are less volatile and have higher viscosity. this is due to stronger induced dipole-dipole forces. they don’t dissolve in polar solvents
what are alkenes
series of hydrocarbons that are unsaturated.
C=C functional group
general formula C(n)H(2n)
more reactive than alkanes
why do alkenes have slightly lower boiling points than alkanes
alkenes have two fewer electrons due to the double bond. this means the induced dipole-dipole interaction is weaker
what is an electrophile
an electron pair acceptor
mechanism of electrophilic addition
- arrow from C=C bond to the δ+ part of the electrophile. electrons in electrophile bond to the δ- part. (double headed arrows)
- the C=C bond becomes a X-C-C+ where X is the δ+ part of the electrophile. the electron pair on the δ- part goes the the C+. (double headed arrow)
- this forms X-C-C-X where X is each part of the electrophile
what is heterolytic fission
the uneven split of a covalent bond. one atom receives both electrons from the bonded pair
how can electrophiles be neutral
the carbon-carbon double bond induces temporary polarisation within the molecule.
why can the electrophilic addition of alkenes produce multiple products
the atom from the electrophile can join either of the carbons in the double bond. e.g. the reaction of but-1-ene and HBr can form 1-bromoButane or 2-bromoButane. this only applies if the alkene is not symmetrical
what is a carbocation
a molecule with a positively charged carbon ion.
how is the major and minor product of electrophilic addition determined?
the major product will be the one where the carbocation has the most alkyl groups attached. this is because it’s more stable. (e.g. 1-bromoButane is the minor product and 2-BromoButane is the major)
define polymer
a long chain molecule made from many smaller molecules joined together
define monomer
the small molecules that join together to form a polymer
define addition polymerisation
the formation of polymers from monomers joining together with no by products
how is the display formula of polymers drawn
Display formula of monomers is drawn but the alkyl groups attached to the Carbons in the C=C bond are attached in structural formula form. its put in square brackets that have lines through them (represent the bonding to other monomers). there is an ‘n’ at the bottom right corner outside the brackets (represents the number of monomers in the polymer chain)
what are plasticisers
molecules that push polymer chains apart. this lowers the melting point and tensile strength of the polymer but increases the flexibility.
what’s LDPE and how is it formed
Low density poly(ethene). 200°C and 2000atm. O2 initiator.
the chains are loosely packed due to branching. its flexible and soft. used in plastic bags/cling film
what’s HDPE and how is it formed
high density poly(ethene). 60°C and 2atm.
chains are tightly packed. its stiff and hard. used in buckets/bottles
environmental issues of poly(ethene)
flammable but chemically inert
strong C-C and C-H bonds
no polar bonds
therefore it is non-biodegradable
issues with burning polymers
releases CO2 and toxic gases
some can release HCl causing acid rain
HCl can be removed by using a reacting with a base
methods of dealing with waste plastics
burning to produce electricity
melting and remoulding
cracking to make monomers to make other polymers
steam cracking to make alkanes/alkenes
why are some polymers biodegradable
the monomers are linked by bonds that can be hydrolysed by micro-organisms
what’s a photodegradable polymer
a polymer that breaks down when exposed to light
what’s the H-C-H bond angle in alcohol and why
4 areas of electron density. all 4 are bonding pairs. tetrahedral angle of 109.5°
what’s the C-O-H bond angle in alcohol and why
4 areas of electron density. 2 bonding pairs, 2 lone pairs. lone pairs repel more. (109.5-2(2.5)=104.5)
104.5° angle
how can an alcohol be named if there’s another functional group
the OH can be noted with the prefix ‘hydroxy-‘
e.g. 2-hydroxy propanoic acid
whats the difference between primary, secondary and tertiary alcohols
the number of alkyl groups attached to the carbon that the alcohol group is attached to. for 1° alcohols its 1 alkyl group and for 2° alcohols its 2
why do alcohols have higher boiling points than alkanes
they can form hydrogen bonds and have a permanent dipole-dipole interaction. (both have induced interaction)
how does solubility change as the chain length of alcohols increases
solubility decreases as chain length increases because more energy is required as the induced dipole-dipole interaction will be stronger
what chemicals are used to oxidise alcohols
potassium dichromate and dilute sulphuric acid
half equation of dichromate ions oxidising alcohol
14H+ + 6e- + Cr2O7^2- –> 2Cr^3+ 7H2O
what’s an aldehyde
they contain the C=O functional group at the end of the chain. compounds end with the suffix -al. (e.g. propanal) there’s no number as C=O is always at the end
what’s a ketone
they contain the C=O functional group but not at the end of the chain. compounds end with suffix -one. (e.g. propanone or pentan-3-one) number only needed if carbon chain is 5 or more
why are tertiary alcohols not easily oxidised
the carbon atom that’s attached to the -OH group has no hydrogens available for oxidation
what’s the colour change when oxidising alcohols and why
orange to green
Cr2O7 ^2- ions are yellow
Cr^3+ ions are green
what’s the relative boiling points of aldehydes, ketones, carboxylic acids and alcohols and why
alcohols and carboxylic have higher B.Ps as they have I.D.D, P.D.D and H.B. ketones and aldehydes have lower boiling points as they only have I.D.D and P.D.D
what is heating under reflux
a condenser is placed vertically onto the flask containing the mixture. this prevents any substances from boiling and escaping. instead they condense and return to the flask
how can alcohols be completely oxidised into a carboxylic acid
add excess potassium dichromate. add anti-bumping granules. reflux gently (prevents aldehyde from escaping to ensure complete oxidation). purify using distillation.
how can alcohols be partially oxidised into an aldehyde
add excess potassium dichromate. add anti-bumping granules. immediately distil off the aldehyde. this ensures only partial oxidation. collect in an ice bath (aldehydes have low boiling points)
define ‘homolytic fission’
when a covalent bond breaks and each atom receives one electron from the bonding pair, forming two radicals
