halogenoalkanes & alcohols - past questions Flashcards
from CH3CH2CH2Cl to Ch3CHCH2, what is the reagent & conditions used in the reaction?
- warm alcoholic
- NaOH / KOH
identify a suitable reagent for CH3CH2CH2Cl to CH3CH2CH2CN, and state why this is a particularly useful reaction in organic chemistry.
- warm alcoholic KCN / NaCN
- increases length of carbon chain / number of C in carbon chain
explain why, in reaction involving CH3CH2CH2Cl to CH3CH2CH2NH2 the reactants are heated in a sealed tube.
- heating increases rate of reaction
- reduce loss of NH3 gas while heating
some halogenoalkanes are put into a mixture of ethanol and silver nitrate.
the precipitate forms as a result of reactions between aq. silver ions & halide ions. why are halide ions present in the halogenoalkane which only has covalent bonds?
- halogenoalkane is hydrolysed by water
- C-Hal bond breaks & produces ions
suggest how the rates of hydrolysis depend on the structure of the bromoalkane. suggest a reason for this difference.
- fastest in tertiary & slowest in primary
- weakest C-Br bond as methyl group donates electrons
explain why the formation of alcohols are faster with aq. alkali than water.
OH- is a stronger nucleophile
describe the observations of alcohols with PCL5.
misty/steamy/white fumes/gas
what is the observation with acidified K2Cr2O7?
alcohols oxidised from orange to green
which method, PCL5 or K2Cr2O7 is more preferred? why?
K2Cr2O7 since PCl5 also reacts with alkali / OH- ions
what is meant by the term free radical?
a species with an unpaired electron
what conditions, other than a suitable temperature and NaOH concentration, would produce butan-2-ol in the reaction of 2-chlorobutane with NaOH?
water (to dissolve NaOH / ac5 as solvent)
phosphorus (V) chloride, PCl5, can be used to test for the -OH group.
describe what would be seen when PCl5 is added to butan-2-ol.
steamy/misty/white gas/fumes
give the equation for the reaction of PCl5 with butan-2-ol.
PCl5 + CH3CH(OH)CH2CH3 -> CH3CHClCH2CH3 + HCl +POCl3
a tertiary alcohol A is an isomer of butan-2-ol.
butan-2-ol and A could be distinguished by warming separate samples with a mixture of potassium dichromate (VI) and sulphuric acid. state the observations which would be made with each alcohol.
observation with butan-2-ol: orange -> green
observation with A: no reaction
give the structural formula of the organic product which forms when butan-2-ol is oxidised.
CH3CH2COCH3
explain how infrared spectroscopy could be used to detect whether butan-2-ol has been oxidised.
absorption for O-H bond would disappear
explain the role of the water in a substitution reaction.
acts as nucleophile -> bonds to carbocation
explain the role of the water in an elimination reaction.
acts as an base -> accepts a hydrogen ion
suggest why 1-chlorobutane reacts with water via a different mechanism.
butyl group has a less electron releasing / less inductive effect
therefore has a less stable carbocation
a primary carbocation is less stable than a tertiary carbocation
2-chlorobutane could form 3 different alkenes in an elimination reaction. suggest how they could be formed.
- H+ could be eliminated on either sides
- since double bonds can’t rotate, methyl groups are fixed & forms E/Z isomers
suggest why 2-fluoro-2-methylpropane would react more slowly than 2 chloro-2-methylpropane in an substitution reaction.
C-F bond is stronger
what reagent could be used instead of water to increase the rate of reaction involving 2-fluoro-2-methylpropane? explain why the reagent would have this effect.
NaOH / KOH / OH- / OH- ions
OH- is a stronger nucleophile with more lone pairs
why is a tertiary carbocation formed more readily than a secondary carbocation?
more stable since methyl groups stabilise charge of carbocation
halogenoalkanes are widely used as refrigerants that cool by change of state, typically by boiling.
suggest how halogenoalkanes cool by change of state.
boiling absorbs energy
suggest two properties desirable in a refrigerant.
- low boiling point
- not flammable
- not toxic
- boiling temperature is lower than target temperatures
give the name & displayed formula of the product of cyclohexanol & potassium dichromate (VI) in dilute sulfuric acid.
cyclohexanone
(AS topic 6 questions)
which m/z value could be used to determine the molecular mass?
highest m/z value
cyclohexene can be prepared by reacting cyclohexanol with phorsphoric (V) acid, distilling off a mixture of cyclohexene and water.
devise a 6-step procedure to obtain a pure, dry sample of cyclohexene from the distillate.
[boiling temp of cyclohexene: 83
density of cyclohexene: 0.811 g/cm3]
1- separate cyclohexene from water using a separation funnel
2- discard lower aqueous layer with higher density
3- add drying agent (eg. Na2SO4 / CaCl)
4- seperate cyclohexene from drying agent
5- redistill product
6- collect distillate boiling between 83 degrees & collect pure cyclohexene.
