m6 - y13 organic Flashcards
arenes def
aromatic compounds that contain a benzene ring
problems with Kekule structure of benzene (bromine water, bond lengths, enthalpy change of hydrogenation)
doesn’t decolourise bromine water, no electrophilic addition reactions 
double bonds are stronger than single bonds so are shorter, meaning K thought benzene would be an irregular hexagon, BUT all carbon-carbon bond lengths were actually equal
ΔH less exothermic than expected, meaning real benzene is more stable than K suggested
Kekule structure of benzene vs new idea in terms of p orbitals and electrons
K = p orbitals overlap in pairs (localised)
new = all p orbitals overlap (sideways in both directions), a ring above the sigma bond, a ring below (delocalised π bonding system) there is less repulsion between electrons so benzene is more stable
there are 6 π electrons one from each carbon
phenyl group functional group
C6H5
nitro group atoms
NO2
alkylation def
hydrogen replaced by an alkyl group
Friedel-Crafts reactions: reagents and conditions
a haloalkane in the presence of a hydrogen carrier catalyst
halogenation of benzene reagents and conditions
halogen and halogen carrier catalyst
acyl group
R - C = O
conditions for acyl chloride reactions with benzene
acyl chloride in the presence of a halogen carrier catalyst
reflux
ANHYDROUS conditions
benzene vs alkene in terms of bromination
higher e- density in alkene localised π bond, so bigger induced dipole in Br2
- polarises electrophile more strongly, attracted more strongly, reacts without a catalyst (by addition)
lower e- density in benzene delocalised π bonding system (spread over more than 2 carbons)
- polarises electrophile less strongly, needs a catalyst to make Br+ (by substitution)
- retains extra stability of delocalised π system, addition would permanently destroy it
phenol def in benzene
-OH directly bonded to a benzene ring
physical properties of phenol
hydrogen bonding => high BP compared to benzene (london forces only)
slightly soluble in water (because the benzene ring is non-polar)
how can phenol decolorise bromine easily
the oxygen has a lone pair of e- in its p-orbital, can overlap with and become part of π bonding system, so has a higher e- density than benzene
reagent for nucleophilic addition (turning carbonyls back into alcohols)
NaBH4 (sodium borohydride)
provides H:- nucleophile
test to detect C=O carbonyl group, and then whether it’s an aldehyde or ketone
add 2,4-dinitrophenylhydrazine, colour goes orange. recrystallise, find melting point and compare to literature values
add Tollens reagent (ammoniacal silver nitrate), silver mirror appears with aldehyde (been oxidised to carboxylic acid, silver ions reduced to silver),
remain colourless with ketone
NMR spectroscopy info
uses radiowaves that are absorbed by the nuclei of certain atoms eg C-13 and H-1 (proton)
need an odd number of nucleons
the frequency (called chemical shift) absorbed depends on the environment of the atom
NMR standard used to compare everything to
TMS (tetramethylsilane) is used as standard. the peak is given a value of 0 and all other peaks are compared to it and given a chemical shift δ in ppm
- TMS is inert and non toxic
- volatile so low BP (easy to remove)
- equivalent, all bonds in the same environment so gives a single peak only
NMR solvent used
sample needs to be dissolved in a solvent to dilute it
common solvents are water, benzene, trichloromethane (but we can’t use hydrogen bc it will swamp the spectrum so we use deuterium)
- D2O
- C6D6
- CDCl3
deuterated solvents
interpreting carbon NMR
- number of peaks => gives number of different carbon environments
chromatography is…
an analytical technique used to separate components of a mixture
thin layer chromatography TLC, what is the stationary phase and mobile phase
S = solid eg Al2O3 coating a sheet of glass
M = liquid eg a solvent which moves vertically up the plate
gas chromatography, what is the stationary phase and mobile phase
S = solid or liquid on an inert solid support eg long chain alkane coating the inside of a coiled tube
M = carrier gas eg inert gas like nitrogen
how does separation occur
the components of the mixture have different attractions for the solid and liquid phases so travel at different speeds
TLC = the stronger the adsorption to the stationary phase, the slower they are carried by the mobile phase
GC = the greater the solubility in the stationary phase the slower they are carried by the mobile phase
interpreting gas chromatograms - retention time
time taken for a component to pass from the column inlet to the detector
chemical shift gives us
gives the type of carbon environment ie tells us what groups/bonds surround the carbon
proton NMR gives you this info
number of peaks (or groups of peaks) => gives us number of different proton environments
chemical shift => gives us type of proton environment
relative peak areas => area under peak is proportional to number of protons. usually given as a number above the peak telling us the relative number of protons of each type (ratio)
spin spin coupling => splitting only occurs if protons on neighbouring carbon are different
=> to check if -NH or -OH add D2O shake vigorously and run spectrum again, peak won’t show up as deuterium exchanges with those H
-:CN group called
nitrile group
HCN -><- H+ and -:CN
carboxylic acid properties
soluble - hydrogen bonds with water
boiling points - higher than alcohols, produces a dimer (2 molecules of carboxylic acids form hydrogen bonds between them)
how to make an acid anhydride
2 carboxylic acids react
water is eliminated
using acid anhydride + alcohol to make esters
acid anhydride (splits) and the OH from the alcohol joins one of them to reform a carboxylic acid
other half acid anhydride reacts with alcohol to form ester
hydrolysis of ester using an alkali
ester + alkali —> CARBOXYLATE SALT + ALCOHOL
carboxylate salt = O-
formation of acyl chlorides => SOCl2 + carboxylic acid
SOCl2 + carboxylic acid (eg Ch3COOH) —> Ch3COCl + SO2(g) + HCL(g)
amines - naming them
add methyl/ethyl/propyl/dimethyl etc to amine
also remmeber they only have 3 bonds not 4
addition polymers => mechanism is called
free radical substitution
reduction of a nitrile to an amine (Ctriple bondN) to NH2 reagents
Ni/H2
chirality
carbon with 4 different environments attached
=> no plane of symmetry so they don’t have a superimposable mirror image so they are optical isomers
enantiomers
optical isomers that rotate plane polarised light by equal amounts in opposite directions
=> a mixture containing 50% of each enantiomer is called racemic mixture
which 2 poly groups are formed by condensation polymerisation
polyesters
polyamides
polyesters
dicarboxylic acid and a diol react and form an ester linkage -COO-
produces polyester and water
=> useful as they can be hydrolysed due to the polarity. => biodegradable in nature by water, so will gradually break down when put into landfill
polyamides
formed from dicarboxylic acid and a diamine => amide linkage (-CONH-)
hydrolysis of polyesters
ester group / amide group broken down by acid or base hydrolysis because they are polar
acidic: (reversible reaction, slow)
H+ and H2O
forms dicarboxylic acid and diol
basic:
ester + base —> carboxylate salt + alcohol
hydrolysis of polyamides
acidic:
H+ and H2O
forms dicarboxylic acid and diamine
HOWEVER acid means NH2 can become NH3+Cl-
basic:
NaOH
forms diamine and dicarboxylate salt
amino acid zwitterions
COOH and NH2 reacting internally to form an internal salt
=> exists at a specific pH value called the isoelectric point
amides functional group
R - C =O
|
N
making amides (primary then secondary)
acyl chloride + ammonia = P
acyl chloride + primary amine = S
