m4 - organic Flashcards
functional group def
a group of atoms responsible for the characteristic reactions of a compound
functional group carboxylic acid suffix
-oic acid
functional group ketone suffix and prefix
-one
-oxo
functional group aldehyde suffix and prefix
-al
-oxo
functional group alcohol suffix and prefix
-ol
-hydroxy
functional group ester suffix
alkyl -anoate
eg ethyl ethanoate
skeletal formula rules
no carbons, no hydrogens
- there are Os and OHs though
homologous series def
a series of organic compounds having the same functional group but with each successive member differing by CH2
- there is a trend in physical properties (gradual change)
structural isomer def
compounds with the same molecular formula but different structural formulae
stereoisomerism def
compounds with the same structural formula but with a different arrangement in space
cis-trans isomers
two of the groups attached to each carbon of the C=C are the same
eg HO-C=C-OH
see booklet for diagrams of cis-trans
cis: 2 groups are near each other / facing each other
trans: 2 groups are on opposite side
E/Z isomerism
e = entgegen (opposite)
z = zusammen (together)
most important group that comes off C=C double bond = highest atomic number
are they on same side or opposite
due to restricted rotation of a double bond
bond names in alkanes and why
σ-bonds -> formed by (overlap of orbitals directly between the bonding atoms)
atomic orbitals combine to form molecular orbitals
alkane reactivity
bonds between C and H are strong, so not very reactive
- alkanes do take part in some chemical reactions
boiling point in straight chain alkanes
increases because as chain length increases, number of e- in the molecule increases
london forces increase
more energy required to overcome intermolecular forces
isomeric alkanes
branched chains have lower boiling points than straight chains
branched chains have a smaller surface area for london forces to act through (can’t get as close to each other)
so smaller attraction between molecules
H-C-C-C-C-C-H can get closer to each other than branched
reactions of alkanes
they readily combust with oxygen to produce CO2 and H2O
- if insufficient oxygen, incomplete combustion occurs to produce CO or C, with H2O
(carbon monoxide is poisonous, takes the place of oxygen in haemoglobin (coordinates to an Fe2+ ion which is part of the haem found in rbc’s)
mechanisms, curly arrow
shows movement of a pair of e-
starts from a bond (X-Y) or a lone pair HO:) or a -ve charge (HO-)
only ever from a -ve to a +ve, not other way round
organic reaction mechanisms: homolytic fission
radicals generated (a species with an unpaired e-)
X-Y -> X. + Y.
can be shown by half curly arrows from bond to each atom
alkanes reaction with halogens (CH4 +Cl2)
initiation, propagation, termination
initiation: - first step in a radical substitution reaction
- halogen-halogen bond is broken to form free radicals (with UV light)
Cl2 —UV—> 2Cl.
propagation: (two repeated steps in radical substitution that build up the products in a chain reaction)
- Cl. + CH4 -> HCl + CH3. (Cl causes a CH bond to break and leaves with the H)
- CH3. + Cl2 -> CH3Cl + Cl. (radical Cl. then repeats process)
termination: (two radicals combine to form a molecule)
- Cl. + Cl. -> Cl2
- CH3. + CH3. -> C2H6 ethane
- Cl. + CH3. -> CH3Cl
mechanism def
sequence of steps showing path taken by e- in a reaction
limitations of radical substitution
the propagation step can result in initial product undergoing further substitutions (of unuseful products like chloromethane, dichloromethane, trichloromethane and tetrachloromethane) - this is a chain reaction
alkenes bonds
5 σ bonds (formed by the overlap of orbitals directly between bonding atoms)
π bond between second C-C (sideways overlap of adjacent p-orbitals above and below the bonding atoms)
- this locks double bond in position and prevents rotation (to rotate you have to break π bond, requiring energy)
bond angle of alkenes
120° (trigonal planar)
3 bonding regions around a central atom
addition reactions of alkenes
mechanism: electrophilic addition
alkene + halogen -> haloalkane
- induced dipole (double bond of high e- density repels one end of Br): Br δ+ - Br δ-
- curly arrow from double bond to the Brδ+, curly arrow from Br-Br bond to Brδ-
- this makes Br- + H-C-C-H (if ethene)
Br + (+ on the carbon) - the e- in the π bond are now in the Br- so carbon charge is +)
- Br- covalent bond with + on carbon to make haloalkane
hydrohalogenation of alkenes
mechanism: electrophilic addition
alkene + hydrogen halide -> CHX (not X2)
- curly arrow from double bond to Hδ+, curly arrow from H-Cl bond to Clδ+ (forms alkane with a + on one carbon)
- curly arrow from :Cl- to + on carbon (forms CHX eg chloroethane)
could have isomers formed depending on where halogen goes. halogen goes to most stable intermediate which is a tertiary (3°) carbocation, then 2°, then 1°
- major products will be most stable (Markownikoffs Rule)
hydration of alkenes
mechanism: electrophilic addition
alkene eg propene + water -> alcohol
must have: 300°C, H3PO4, 65atm
- curly arrow from double bond to H+ (catalyst from H3PO4) forms propane with a + on a carbon instead of an H
- curly arrow from one of the pairs of e- in water to the + carbon
- forms propanol with an extra H on the OH and the O has a + charge
- curly arrow from one O-H bond to the O
- forms propanol + H+ (the catalyst that can be reused again)
hydrogenation of alkenes (reduction)
alkene + hydrogen -> alkane
needs Ni and 150°C
what is an electrophile
an electron pair acceptor
addition polymerisation
alkene -> break double bond and add square brackets (repeat unit)
alkene becomes a polyethene
if asked to draw a number of repeat units of a polymer, outward bonds but no brackets or n
alcohols formula
CnH2n+1OH
IMF in alcohols
hydrogen bonding between molecules (e- deficient H, and highly electronegative O)
properties of alcohols (solubility and boiling point)
likely soluble in water - similar strength attractions between water and alcohol molecules
decreases as chain length increases - a larger part of the molecule is made of non polar C-H bonds, and hydrocarbon chains don’t form H bonds with water
bp higher in alcohols than alkanes - alcohols have H bonding and alkanes have london forces
classification of alcohols , primary secondary tertiary
primary: C attached to one other C (C-COH)
secondary: C attached to 2 other Cs
tertiary: C attached to 3 other Cs
combustion of alcohols
oxygen in excess or not (incomplete to form CO or C)
oxidation of alcohols , what is used and colour it goes
acidified potassium dichromate H2SO4/K2Cr2O7 (represented by [O] in equations)
K2Cr2O7 = ORANGE (oxi number = +6)
when reduced (mixed with alcohol) = GREEN (oxi number = +3)
primary alcohol oxidation
primary alcohol + potassium dichromate [O] -> aldehyde + water
aldehyde + [O] -> carboxylic acid
to obtain aldehyde, reaction needs DISTILLATION apparatus so aldehyde distils off as soon as it forms and doesn’t have time to oxidise further
to obtain COOH, REFLUX apparatus should be used, allows aldehyde to condense back into reaction flask and carry on reacting
dealing with polymer waste - combustion
plastics have high calorific value so can be burnt in power stations
the chemical energy transferred can be used to drive turbines and generate electricity
dealing with polymer waste - organic feedstock
plastic polymers can be broken up into small organic molecules. recovered chemicals can be used in other industrial reactions
polymer waste - dealing with toxic waste products
HCl gas made from the combustion can be removed using gas scrubbers - bases such as CaO neutralise acidic gas
controlling oxidation of primary alcohols (conditions)
reflux - aldehyde made will condense back in and oxidise further to a carboxylic acid
distillation - once aldehyde is made it is distilled away
oxidation of secondary alcohols
oxidised to ketones under reflux conditions to ensure all reactant is converted to product
oxidation of tertiary alcohols
resistant to oxidation
elimination of water from alcohols (dehydration), conditions
concentrated acid catalyst eg conc H2SO4 or H3PO4
heat at reflux for 40mins
alcohol —> alkene + water
substitution of alcohols to give haloalkanes, conditions
conc H2SO4 and NaCl/NaBr
ROH + HX —> RX + H2O
nucleophilic substitution (Sn2)
ester reactions
REVERSIBLE
ethanoic acid (Xanoate) + alcohol (Xyl)
eg ethyl butanoate (ethanol and butanoic acid)
nucleophile def
electron pair donor
(attacks region of low electron density δ+)
nucleophilic substitution - haloalkanes with aqueous alkali (OH:-)
curly arrow: lone pair on OH:- to C with a δ+
curly arrow: C-X bond to X with δ-
haloalkane + OH:- —> alcohol + X:-
hydrolysis of haloalkanes and water
adds ethanol and water and using AgNO3 to form halides (at 50°C)
measures time taken for precipitate to show
iodoalkanes react fastest due to lowest bond enthalpy (has low polarity but that’s less important)
chloroalkanes react slowest due to highest bond enthalpy (high polarity but unimportant)
how does the ozone layer protect us
from harmful UV radiation from the sun (all UV-C, most UV-B)
mechanism of ozone destruction by CFCs
initiation: C2F2Cl2 —> C2F2Cl. + .Cl
propagation: Cl. + O3 —> ClO. + O2
ClO. + O3 —> Cl. + 2O2
overall: 2O3 -> 3O2
