An alcohol is an alkane in which one hydrogen is replaced by the OH functional group.
A primary alcohol is an alcohol where the carbon atom attached to the OH group is attached to 1 carbon atom.
A secondary or tertiary alcohol is where it is attached to 2 or 3 carbon atoms respectively.
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Alcohols (cont)
Alcohols react with solid sodium to form hydrogen gas and a solid sodium oxide.
The Na substitutes for the alcoholic hydrogen.
You see effervescence, the sodium disappearing and a new solid forming.
Example of sodium oxide is sodium propoxide (from propan-1-ol). This is ionic.
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Alcohols (cont)
When you react primary, secondary or tertiary alcohols with a halogen atom, a halogenalkane forms.
All alcohols react with phosphorus (V) chloride (solid), PCl5, to form the liquid chloroalkane, HCl gas and POCl3 (liquid).
All alcohols react with concentrated HCl (aqueous) to form the chloroalkane and water.
Both are substitution reactions.
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Alcohols (cont)
Complete combustion of an alcohol forms carbon dioxide and water vapour.
This is the simplest oxidation reaction of alcohols.
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Alcohols (cont)
For all the following oxidation reactions, the oxidising agent is acidified potassium dichromate.
As the dichromate ion (Cr2O7-) is reduced to chromium ion (Cr3+), it changes colour from orange to dark green.
The acid used to acidify the solution is sulphuric acid.
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Alcohols (cont)
Primary alcohols that are oxidised and distilled immediately form aldehydes.
Dilute sulphuric acid should be used to acidify solution
Aldehydes form a red precipitate when boiled with Benedict's or Fehling's solution.
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Alcohols (cont)
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Alcohols (cont)
Primary alcohols that are oxided and heated under reflux before being distilled are oxidised further to form carboxylic acids.
Concentrated sulphuric acid should be used to acidify solution.
Carboxylic acids will neutralise large volumes of sodium carbonate solution.
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Alcohols (cont)
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Alcohols (cont)
When secondary alcohols are oxidised they always form ketones, which cannot be oxidised further.
Ketones form a yellow/orange precipitate with Brady's reagent.
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Mass Spectra and Infrared Absorbtion
The mass spectrum of an organic compound tells us 2 main things.
The tallest peak, from the molecular ion, tells us the relative molecular mass of the compound.
The other peaks are from smaller fragement ions.
These ion peaks indicate likely functional groups.
A molecule can lose each part consecutively from either side to form an ion. Ethanol can lose the -H, -OH, or -C2OH. It can also lose the CH3 from the opposite side
So there is a total of 5 peaks in the mass spectrum.
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Mass Spectra and Infrared Absorbtion (cont)
Molecules absorb infrared radiation by vibrating with increased kinetic energy.
Different bonds have different vibrational frequencies, which depend on the bond strength.
A specific IR is required to make a certain bond vibrate, and can be seen in an absorbtion spectrum.
The unit of measurement for absorbance is wavenumber, a receprical of wavelength.
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Mass Spectra and Infrared Absorbtion (cont)
Only molecules that change polarity as they vibrate (due to dipole movement in polar bonds) absorb IR.
So molecules without a dipole (oxygen and nitrogen) do not absorb IR.
Only molecules that can absorb IR are greenhouse gases.
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