organic chem year 2👹👹👹 Flashcards
product when phenol reacts with bromine
observation
2,4,6-tribromophenol
white ppt
goes colourless
product when cyclohexene reacts with bromine
1,2-dibromocyclohexane
explain the relative resistance to bromination of benzene compared to phenol and compared to cyclohexene
- benzene electrons are delocalised
- phenol lone pair of electrons from oxygen are delocalised into ring
- cyclohexane electrons are localised
- benzene has lower electron density than phenol and cyclohexane
- benzene cannot polarise Br2
difference in bonding between the two models of benzene
-p orbitals overlap
(in model with 3 double bonds)
-pi bonds localised
(in model with delocalised ring)
-pi bonds delocalised
ways to synthesise esters
carboxylic acid + 1 alcohol
acyl chloride + 1 alcohol
acid anhydride + 1 alcohol
how to name ester
- second part refers to chain double bonded to oxygen
- first part refers to chain on other side of oxygen in the middle
for reaction between acid anhydride and alcohol
- conditions
- products
- impact of each reactant on final product
- no catalyst
- ester and carboxylic acid
- acid anhydride gives second chain with double oxygen bond
- alcohol gives first section
for reaction between acyl chloride and alcohol
- conditions
- products
- impact of each reactant on final product
- no catalyst
- ester and HCl
- acyl chloride gives second chain with double oxygen bond
- alcohol gives first chain
describe what is happening to the electron pairs in the first step of nucleophilic substitution (NaBH)
- electron pair on H- is attracted to slightly positive carbon forming dative covalent bond
- double electron pair breaks
- electron pair now on O-
Butanal and butanone both react with 2,4-dinitrophenylhydrazine to produce mixtures containing orange precipitates.
Outline how the mixtures containing these orange precipitates can be used to distinguish between butanal and butanone.
- recrystallise precipitate
- measure melting point
- compare with known values
Describe a simple chemical test that would show that but-2-enal is an
aldehyde.
- heat with Tollens reagent
- silver mirror
Explain why Tollens reagent gives a different result with aldehydes than it does with ketones.
- aldehydes can be oxidised to carboxylic acid
- aldehydes can reduce Ag+ to Ag
Tollens’ reagent can be used to identify the aldehyde group in cinnamaldehyde
Describe how you would make Tollens’ reagent and carry out this test in the laboratory.
Explain what happens to both the Tollens’ reagent and the cinnamaldehyde in this reaction. Identify the organic product.
- silver nitrate and ammonia to make Tollens reagent
- heat
- silver mirror forms
- Ag+ ions reduced
- aldehyde oxidised to carboxylic acid
- C6H5CHCHCOO-
products of reaction between nitrobenzene, tin and hydrochloric acid
phenylammonium chloride
water
products of reaction between phenylammonium chloride and sodium hydroxide
phenylamine
water
sodium chloride
phenol to hydroxypheylamine
HNO3
phenylammonium chloride to phenylamine
add NaOH
a mixture of tripeptides can be analysed by using gas chromatography, coupled with mass spectrometry.
Summarise how each method contributes to the analysis.
gas chrom- separates tripeptides
mass spec- produces distinctive fragmentation pattern
-identification by computer using spectral database
general formula of alpha amino acid
RCH(NH2)COOH
Explain what structural feature causes optical isomerism in organic molecules.
- chiral
- 4 different groups
- mirror images cannot be superimposed
Name a suitable reagent and conditions for the hydrolysis of polypeptide
- aqueous HCl
- under reflux
- enzyme at 37 degrees
state a use for a tough polypeptide
- fire resistant clothing
- tyres
- tennis racket
explain why branched chains have lower boiling point
- less surface interaction between molecules
- weaker london forces
- require less energy to break
Describe a method to obtain a pure sample of 3-nitrobenzoic acid from the impure solid and check purity
- recrystallise
- dissolve in hot water
- cool solution and filter solid
- wash with cold water and dry
- find mp and compare with known values
- pure will have mp close to data book value
why is phenol easier to nitrate than benzoic acid
- phenol has lone pair from o delocalised into ring
- ring more susceptible to attack
- benzoic acid has an electron withdrawing group
- ring less susceptible to attack
reduction of bromonitrobenzene reagents
Sn
HCl
why does bromination of nitrobenzene and phenylamine put Br in different places
NH2 is 2,4 directing
CN to COOH
aqueous H2SO4
CN to CH2NH2
H2 Ni
why does an amine form a salt with HCl
accepts proton
nitrogen has a lone pair
why are condenstion polymers biodegradable (ester)
ester bond can be hydrolysed
aldehyde to alcohol
NaBH4
phenol reaction with na2co3
no reaction
carboxylic acid reaction with na2co3
carbon dioxide produced
State and explain how the halogen in the haloalkane affects the rate of hydrolysis
- weaker bond= faster hydrolysis
- C-F bond is strongest so hydrolysed slowest
aldehyde to CHOH(CN)
NaCN/H+
CN + H+ forms
COOH
NaOH reaction with OH and COOH
OH: O-Na+
COOH: COO-Na+
Na2CO3 reaction with OH and COOH
OH: no
COOH: COO-Na+
carboxylic acid to acyl chloride
PCl5
why does hexane have a lower bp than heptane
- heptane has more points of contact
- heptane has more London forces
- more energy needed to overcome forces
why does a carboxylate salt need to be acidified in order for crystals to appear
protonates salt
safety precaution with lead
wear gloves because lead is toxic
test for phenol
Br2 makes white ppt
reacts with NaOH does not react with carbonates
E/Z vs cis/trans isomers
- in EZ all 4 groups can be different
- in cis trans at least 2 groups need to be the same
why can a ring display only one of E or Z isomer
-the ring would have to break to display the other isomer
what is the reference compound for NMR
tetramethylsilane
Si(CH3)4
what solvent is used for NMR
CCl4
what is D2O used for in NMR
makes the NH or OH peak disappear as the H exchanges with D
