4.2 alcohols & haloalkanes Flashcards
state and explain the trend in boiling point of alcohols - 4 points
- as chain length increases boiling point increases…
- …because there are more electrons in longer chains…
- …stronger dipole and induced dipole-dipole interactions…
- …more energy needed to break the bonds.
how does branching affect the boiling point of alcohols? state and explain - 4 points
- more branching = lower boiling point
- branches on chains mean there is less surface contact between molecules
- so they are further away from each other
- so the induced dipole-dipole interactions are reduced.
what is the functional group of the alcohols and what is it called?
-OH it is the hydroxyl group
why are alcohols polar? explain how this forms hydrogen bonds
they are polar because the hydroxyl group is electronegative
the electronegative O in the C-OH bonds draws electron density away from the H, making it delta+
this H attracts lone pairs from neighbouring Os in other molecules which creates hydrogen bonding.
describe why alcohols are soluble in water
the alcohols form hydrogen bonds with the water molecules, allowing them to dissolve in the water
compare the boiling points of alkanes and alcohols and explain this
alcohol bp > alkane bp
alcohols have higher boiling point due to hydrogen bonds in the -OH group
these bonds require more energy to break.
why do alcohols have a relatively low volatility?
the strong hydrogen bonds prevent them from evaporating easily into a gas.
what is a primary alcohol?
when the -OH group is attached to a C which is attached to ONE other C.
the C attached to the -OH group is attached to 2 hydrogens.
what’s a secondary alcohol?
when the -OH group is attached to a C which is attached to TWO other Cs.
the C attached to the -OH group is attached to only ONE hydrogen.
what is a tertiary alcohol?
when the -OH group is attached to a C which is attached to THREE other Cs.
the C attached to the -OH group has NO hydrogens attached to it.
give the general word equation for the combustion of alcohols
alcohol + oxygen –> carbon dioxide + water
name and give the symbol of the oxidising agent used int he oxidation of alcohols
acidified potassium dichromate - Cr₂O₇²⁻/H⁺
where K⁺ and SO₄²⁻ are spectator ions
how does the acidified potassium dichromate tell us an oxidation has taken place?
it is an orange solution and turns green when it has been reduced/oxidised the alcohol
which type of alcohol does not oxidise?
tertiary alcohols do not because they are very resistant to oxidation.
what do secondary alcohols form when oxidised?
name the functional group and the stem of this molecule
ketone + water
ketone has functional group C=O and the stem is ‘one’ eg. methanONE, propanONE.
name the two ways in which a primary alcohol can oxidise
by distillation and by reflux
what is reflux? why is it used?
the constant boiling and condensing of a reaction mixture.
used to make sure the reaction goes to completion
what is produced when a primary alcohol is oxidised under distillation?
name the functional group and stem of this product
aldehyde + water
aldehydes have functional group -CHO and stem ‘AL’ eg. methanAL, propanAL
in an equation, what can an oxidising agent be abbreviated as?
[O]
what is produced when a primary alcohol is oxidised under reflux?
name the functional group and stem of this product
carboxylic acid (water not produced)
FG: -COOH
stem: -oic acid, eg. menthanOIC ACID, propanOIC ACID
carboxylic acid + alcohol –> ?
ester + water
how can alcohols form haloalkanes? what catalyst is needed?
- they react with compound containing halide ions eg. NaBr
- the hydroxyl group is replaced by the halide and so it becomes a haloalkane
- the reaction requires an acid catalyst, eg. H2SO4
how can an alcohol become an alkene? what conditions are needed?
- by eliminating the water in an alcohol (dehydrating it)
- acid catalyst needed - concentrated sulphuric acid (
H2SO4) or concentrated phosphoric acid (H3PO4) - the mixture must be HEATED
name and describe two trends in the boiling point of haloalkanes
- bp increases as C chain increases - more electrons - stronger induced dipole-dipole interactions - harder to break
- bp decreases down - C-Cl bond has higher enthalpy - more energy needed to break
C-I - lower bond enthalpy
why can haloalkanes undergo nucleophilic substitution?
because the C-halogen bond is electronegative with the halogen being delta- and the C being delta+
define nucleophile
an electron pair donor
what’s it called when a haloalkane becomes an alcohol? state the conditions required for this reaction and give 3 steps of the reaction
hydrolysis - reacting with OH- ions MUST have a WARM AQUEOUS ALKALI 1. the delta+ C accepts the lone pair of electron from the nucleophile :OH- 2. this forms a C-OH bond 3. the halogen is removed eg. :Br-
how does the halogen on the alkane affect the rate of hydrolysis?
the higher polarity in the C-X bond, the stronger the bond.
eg. C-F is the most polar - strongest bond - HIGHER BOND ENTHALPY - so slower hydrolysis
C-I is least polar - weakest bond - low bond enthalpy
how are radicals formed in the atmosphere?
CFCs in the atmosphere absorb UV light
what do the radicals in the atmosphere contribute to?
write 4 equations of the CFC CF₂Cl₂ doing this
the depletion of the ozone layer CF₂Cl₂ -> CF₂Cl• + Cl• Cl• + O₃ -> ClO• + O₂ ClO• + O -> Cl• + O₂ O + O₃ -> 2O₂
write 3 equations of how the radical •NO contributes to the ozone depletion
•NO + O₃ -> •NO₂ + O₂
•NO₂ + O -> •NO + O₂
O₃ + O -> 2O₂
how is the concentration of ozone in the atmosphere maintained? (use an equation)
O₃ ⇋ O + O₂
the rate of the forwards and backwards reaction is the same
what is infrared spectroscopy used for?
identify a different compound
identifying functional groups
how does IR spectroscopy identify compounds?
bonds absorb IR radiation and they vibrate
different bonds absorb different frequencies
give 3 uses of infrared spectroscopy
- tracking green house gas levels
- monitor pollution from cars
- used in breathalysers - C-O is detected to find ethanol bc o-h bonds are in our breath anyway
what is mass spectrometry used for?
molecular mass of compound
fragment patterns - make up of the compound
on the mass spectra, where can you identify the molecular mass of the whole compound?
peak with the high m/z value is the overall mass
what are the lower m/z peaks on the mass spectra called?
fragment ions
